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Unit 2 Mineralogy

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    Notes on Engineering Geology for Civil enggCompiled by Dr G SUBBARAOM.Sc. ,M.Phil., Ph.D., C.S.M.

    UNIT: II - MINERALOGY

    Mineral: The study of the characters of minerals ( eg: quartz, pyroxene,

    amphibole, mica, chlorite, garnet) is known as Mineralogy. A mineral is a naturally

    occurring homogeneous substance, inorganically formed with a definite chemical

    composition, with a certain physical properties and crystalline structures

    Under favourable conditions, the internal atomic structure of minerals result in

    the development of a definite external geometrical shape ie crystal form.

    The stability of minerals depends on temperature, pressure and chemical

    composition of the environment. At present more than 3000 mineral species

    have been established.

    The earths crust is mainly composed of feldspars and quartz and accounts

    55% and 10% respectively. Pyroxenes, amphiboles, chlorites, micas, clay

    carbonates are widely spread too. Following a few rare minerals are also common:

    Phenacite Be2(SiO4) Bertrandite Be4(Si2O7) (OH)4

    Baddeleyite Zr O2 Cordierite Hg3 S2Cl2

    Explanation:

    Homogeneous : all parts of the minerals should possess the same physical and

    chemical characters.

    Crystalline: possess atomic structure in a mineral.

    Crystal: A crystal may be defined as a natural solid body bounded by smooth

    and plain surfaces, arranged geometrically.

    Crystals develop under favourable conditions depending on: (1) slow cooling (2)

    surroundings to facilitate the crystal growth in different directions. (3) non-

    interference by the adjacent growing minerals during solidification.

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    Exceptions for Definition of Mineral:

    l. Precious gemstones like diamonds, rubies, sapphires and emeralds are

    synthetically produced under controlled laboratory conditions.

    2. Coal, amber, petroleum, etc., are typical organic substances which can beconsidered as minerals.

    3. Amethyst, smoky quartz, citrine, cat's eye, aventurine quartz are some varieties of

    quartz. Colour or appearance peculiarity in them is because they possess some

    impurities or inclusions or in homogeneities.

    4. Asphalt ( a variety of bitumen, semi-solid in nature, black in color) , mercury and

    natural gas are semisolids, liquids or gases. Though these are called minerals, they

    are not solid substances.

    5. A good number of minerals are now found to be members of isomorphic groups.

    Isomorphic minerals do not have a definite chemical composition, but have a definite

    range of composition.

    6. Some minerals like flint, chert, jasper and agate are cryptocrystalline, i.e., they do

    not have a well-developed crystal structure. A few others like opal, bauxite,

    Psilomelane, pitchblende etc are typically amorphous, i.e., they do not possess any

    regular internal atomic structure.

    The most widespread elements in minerals are: O, Si, Al, Fe, Ca, Na, Mg, K, Ti

    while S, Cl, C, Mn, H are moderately spread. B, Be, Pb, Sb, As, Bi, Se, U, etc

    are either rare earth elements or not spread at all.

    Minerals are broadly grouped into

    (a) Rock forming minerals ( constitute a rock ) and

    (b) Oreforming minerals (composition of an ore which is economically imp ).

    The term ore mineral embraces minerals from which valuable metallic elements

    can be extracted. Eg; Cu, Ag, Fe, Al.

    Minerals are extremely important economically, aesthetically, industrially and

    scientifically.

    Economically, utilization of minerals is necessary to maintain anything for

    standard of living. Gold, silver, copper, iron, aluminum etc are economically

    important minerals for human beings.

    Aesthetically, minerals of diamond, ruby, sapphire, emerald shine as gems

    and enrich our lives. Gems in jewellery, crown jewel collections attract the

    attention of millions of people.

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    All in all, approximately 10% of all mineral species are used at present for

    industrial purposes.

    Scientifically, minerals comprise the data bank from which we can learn about

    our physical earth and its constituent materials.

    Chemistry has developed on the basis of the study of the chemical composition

    and the properties of various minerals and ores. Mineralogical methods are widely

    used in Petrology, Geochemistry, soil study, Paleontology (in the study of

    fossils), in medicine, in archeology.

    All the minerals are grouped into 8 classes:

    1. Native elements (Eg: Au, Ag, Cu, Arsenic, Bismuth, Platinum, Diamond)

    2. Sulphides ( Eg: Galena, Pyrite, Cinnabar, Stibnite, Pyrrhotite)

    3. Oxides (Magnetite, Haematite, Rutile, Brookite) and hydroxides (Eg:serpentine; amphiboles)

    4. Halides (Eg: Fluorite, Halite)

    5. Carbonates ( Eg: calcite, Magnesite), nitrates and borates

    6. Sulphates ( Eg: Barytes, Gypsum), chromates (Eg: Uvarovite)

    7. Phosphates ( Eg: Apatite, Monazite)

    8. Silicates ( eg: Quartz, feldspars, Muscovite, Biotite, Hornblende, Tourmaline,

    Zerolite, Topaz ) .

    Since silicates are the most common rock forming minerals, it is desirable to

    know some relevant aspects about these.

    In all silicate structures, the silicon atoms are in fourfold coordination with

    oxygen. The bonds between silicon and oxygen are so strong that the 4 oxygens

    are always at the corners of a tetrahedron of nearly constant dimensions.

    O

    O

    O

    O

    Si

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    STRUCTURE OF SILICATES / CLASSIFICATION OF SILICATES

    Silicate classification for most silicate minerals is based on the types of

    linkages as follows:

    1. NESO SILICATES2. SORO SILICATES

    3. INO SILICATES

    4. CYCLO SILICATES

    5. PHYLLO SILICATES

    6. TECTO SILICATES

    1. NESOSILICATES: ( independent tetrahedral groups ): in this group SiO4

    tetrahedra occur as independent units in mineral structure.

    Si : O : : 1 : 4

    One siliconoxygen tetrahedron

    Eg: Olivine family;

    Aluminum silicate family ( kyanite , sillimanite; Andalusite )

    Garnet family.

    OLIVINE FAMILY

    OLIVINES are nesosilicates in atomic structure with the general formula

    R2 ( SiO4) in which R = Mg or Fe. Olivine family consists of

    Forsterite ( Mg2SiO4)

    Fayalite ( Fe2SiO4 )

    Olivine (Mg Fe)2SiO4

    Olivine is one of the first minerals to form alongwith calcic plagioclase feldspars

    during the solidification of magma. As magma cools down, olivine reacts with

    silica content of parent magma and changes over to pyroxene.

    PERIDOT is a transparent, pale green gem variety found in Egypt, Burma, Brazil )

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    Alteration: olivines are highly susceptible to decomposition. Hydrothermal

    alteration of olivines produces serpentine.

    3 Mg2SiO2 + H2O + SiO2 2 Mg3Si2O5(OH)4

    Forsterite serpentineOccurrence: Occurs in Ultrabasic igneous rocks such as Dunite, Peridotite,

    Picrite . Also occurs as accessory mineral in Basalts, Dolerites, Gabbros.

    Uses: Due to its high melting point, olivine is used in the manufacture of

    refractory bricks.

    ALUMINUM SILICATES

    In nature, totally, three minerals with different physical properties with same

    composition occurs as Al2SiO5, which are called as aluminum silicates .

    ANDALUSITE formed under high temperature & low stress conditions of

    metamorphism.

    SILLIMANITE formed under high temperature & high stress conditions of

    metamorphism.

    KYANITE formed under moderate temperature and high stress conditions of

    metamorphism. Kyanite is a product of high grade metamorphism. It will notform either as a primary mineral or as a product of weathering.

    GARNET FAMILY

    This family is also belonging to nesosilicates and consist of the following

    minerals:

    Grossular Ca3Al2 (SiO4)3

    Almandine Fe3Al2 (SiO4)3

    Pyrope Mg3Al2 (SiO4)3

    Spessartite Mn3Al2 (SiO4)3

    Andradite Ca3Fe2 (SiO4)3

    Uvarovite Ca3Cr2 (SiO4)3

    Under microscope, garnet can be seen rounded crystals , traversed by branching

    cracks and having no cleavage.

    Occurrence: Gneisses, Kyanite Schists; Syenites etc

    Uses: used as abrasive in the polishing of wood and as a gemstone.

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    2. SOROSILICATES:(Double tetrahedral structures): in this group of minerals,

    SiO4 tetrahedra occur in pairs in which one oxygen is shared between the two

    silicon atoms. The epidotes are all similar in their atomic structure, a mixed

    type containing both SiO4 and Si2O7 groups forms a different types of minerals

    eg: Idocrase.

    (Si : O : : 2 : 7) Two siliconoxygen tetrahedron

    Epidote family consists of Zoisite .. Ca2Al3(SiO4)3 OH

    Epidote.. Ca2 (Al, Fe)3 (SiO4)3 OH

    Allanite.. (Ca, Fe)2 (Al,Fe,Ce)3(SiO4)3 OH

    Melilite . Ca2Mg Si2O7

    Hemimorphite Zn4Si2O7(OH)2H2O

    Idocrase .. Ca10Al4(Mg,Fe)2(Si2O7) (SiO4)5 (OH)4

    O

    OO

    OO

    SiSi

    O

    O

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    3. INOSILICATES: Two varieties of inosilicates (single chain & double chain

    structures) occur in nature.

    SINGLE CHAIN SILICATES Si : O : : 1 : 3

    In this group of minerals, SiO4 tetrahedra occur as chains resulting in moregrowth of minerals along one direction. The chains consist of a large number of

    linked SiO4 tetrahedrons, each sharing two oxygens. Eg: pyroxenes

    The pyroxenes are a group of minerals which possess the Si2O6 chain

    structure. Pyroxenes consist of:

    Pyroxens Composition Occurs in

    Enstatite Mg Si O3or Mg2Si2O6 Igneous rocks such as Gabbros,Diorites; Peridotites, Serpentinites

    Hypersthene (Mg, Fe ) SiO3 Norite, Gabbros; Andesite;Charnockites; Schists; Hornfels

    Diopside Ca Mg Si2O6 Pegmatites; Granites

    Hedenbergite Ca Fe Si2O6 At contact of granitic rocks withlimestones

    Pigeonite (Ca Mg) (Mg Fe) Si2O6 In volcanic rocks

    Augite (Ca Mg Fe Al)2 (Al ) Si2O6 Occurs as short prismatic crystals in

    volcanic rocks such as Andesite,Basalts. Basic igneous rocks ofGabbros; dolerites, diorites and inUltrabasic igneous rocks such asPeroxenites; Peridotites.

    Aegirite Na Fe Si2O6

    Jadeite Na Al Si2O6

    Spodumene Li Al Si2O6 Pegmatites.

    Si

    Si

    SiSi

    Si Si Si

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    AUGITE : It is a silicate of calcium, magnesium, iron and aluminum with a

    composition of (Ca Mg Fe Al)2 (Al ) Si2O6. It forms as a crystals, lamellar and

    sometimes fibrous.. Augite occurs in Black and greenish black in color.

    Varieties: Diallage is a variety of augite which in hand-specimen appears as

    lamellar ( lamellar structure is due to a parting parallel to the planes ).

    Diallage is characteristic of Gabbros.

    Occurrence: augite occurs as short prismatic crystals in volcanic rocks,

    Andesite, basalts etc.. and as crystals or plates in dykes and in plutonic rocks

    such as gabbros, dolerite and in diorite. It also occurs in Ultrabasic rocks

    such as pyroxenites and Peridoties.

    DOUBLE CHAIN SILICATES Si : O : : 4 : 11

    The amphibole group possess Si4 O11 double chain type of structure where

    Tetrahedra are joined together to produce chains of indefinite extent. The

    general formula for amphibole group is X 78 (Si4O11)2 (OH)2 where x = Ca,

    Na, Mg, Fe+2; Al; Fe+3 .

    Amphiboles Composition Occurs in

    Anthophyllite ( Mg,Fe+2)7(Si8O22) (OH)2 Anthophyllite schists, gneisses

    Cummingtonite ( Mg,Fe)7(Si8O22) (OH)2 In metamorphic rocks

    Grunerite ( Fe, Mg )7(Si

    8O

    22) (OH)

    2

    Tremolite Ca2 Mg5 Si8 O22 (OH)2 In Serpentinites, greenstones,Actinolite schistsActinolite Ca2 (Mg,Fe)5 Si8 O22 (OH)2

    Hornblende (Ca Na Mg Fe Al)7-8Si8 O22(OH)2

    Granites; Syenites; diorites, Hblgneisses; hbl schists, amphibolites

    Glaucophane Na2(Mg Fe)3(Al Fe+3) Si8

    O22(OH)2Soda rich ig rocks ie glaucophaneschists

    Riebeckite (Na2Fe+ ) (Fe+ )3 (Fe

    + )2Si8O22(OH)2

    Nepheline schists, pegmatites.

    HORNBLENDE: It is a silicate of aluminium, calcium, magnesium and ironwith sodium represented by the formula (Ca Na Mg Fe Al)7-8 Si8 O22 (OH)2.

    Hornblende occurs as crystals, prismatic in habit.

    Varieties: Edenite is a light coloured hornblende poor in iron where as

    Pargasite is a darkgreen or bluish green variety and basaltic hornblende is

    a brown or black variety containing titanium and sodium.

    Occurrence: It occurs as a primary mineral in acid and intermediate igneous

    rocks such as granites, Syenites, diorites etc and Ultrabasic rocks viz.,

    hornblendite and common in metamorphic rocks of hornblende gneisses,hornblende schists and amphibolites.

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    ASBESTOS: The term asbestos is a commercial name which indicates fibrous

    varieties of several minerals differing widely in composition. The fibres are

    flexible and easily separated by the fingers. The color of asbestos varies from

    white to greenish and brownish. Asbestos is classified in two different groups:

    (1) the serpentine group which includes the elastic and silky chrysotile variety

    and the woody fibre varietypicrolite and

    (2) the amphibole group which comprises the short and brittle fibred type ie

    anthophyllite, crocidolite, amosite, tremolite and actinolite.

    The commercial asbestos include the following fibrous minerals:

    CHRYSOTILE (fibrous serpentine of hydrous magnesium silicate with a

    composition of Mg6(Si4O10) (OH)8).

    AMOSITE (fibrous anthophyllite of magnesium iron silicate with a composition of

    ( Mg,Fe+2)7 (Si8O22) (OH)2.Occurs in metamorphic rocks usually derived from

    anthophyllite schists & gneisses.

    CROCIDOLITE ( a fibrous soda amphibole which is a variety of Riebeckite,

    indigo- blue in colour found in A. Africa. Occurs in acid igneous rocks rich in

    Na ie Riebeckite-granite, Riebeckite granophyres etc.

    ASBESTOS DEPOSITS OF INDIA: Most of the Indian asbestos deposits belongto the tremoliteactinolite variety. It occurs in tremolite-act schists, amphibolites etc.

    Bihar, Rajasthan, Gujarat, AP ( Kurnool and Cuddapah and anantapur districts)

    and Tamil Nadu producing the commercial asbestos.

    GENESIS OF ASBESTOS: Three main factors are responsible for the

    formation of asbestos in schistose rocks, Peridotites, Dunites and Serpentinites.

    The factors : (1) serpentinisation in the formation of chrysotile asbestos

    (2) transformation of non-fibrous serpentine into the fibrous mineral and

    (3) the gradual change of chrysotile into tremolite asbestos.

    Uses: The usefulness of asbestos depends upon its resistance to heat property.

    1. used for gaskets & insulating material and for spark plug gaskets.

    2. Asbestos fibres are mixed with Portland cement for the manufacture of

    corrugated and plain sheets and different types of asbestos pipes.

    3. Asphalt asbestos used for roofing purposes.

    4. Asbestos cheaper grade is utilized for the manufacture of asbestos paper.

    5. Asbestos paper is extensively used for heat and electrical insulation

    purposes and also for spark plug gaskets.

    6. Used as a refractory material by mixing asbestos powdered with Magnesite

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    4. CYCLO SILICATES(Ring structures): When each SiO4 tetrahedron shares

    two of its oxygens with neighbouring tetrahedra, they may be linked into rings.

    ( closed rings of tetrahedra each sharing two oxygens ) - These are also called

    ring silicates.

    In this group of minerals, 3 or 4 or 6 tetrahedra occur in ring form.

    Eg for 3 tetrahedra : Bentonite ( Ba Ti Si3O9)

    Eg for 4 tetrahedra : Axinite Ca2(Fe,Mn) Al2 (BO3) (Si4O12) (OH)

    Eg for 6 tetrahedra : Beryl ( Be3Al2Si6O18 )

    Cordierite (Mg Fe)2 (Al3Al Si6O18)

    Tourmaline: X Y3 B3 ( Al, Fe)6 O27 (OH,F)4 where

    x = Na, Ca and Y = Mg. Fe, Al, Li

    Varieties: Rubellite --- red or pink in color.

    Indicolite --- Indigoblue color

    Brazilian emerald --green in color ( transparent )

    Schorl --- Black in color ( opaque )

    Occurrence: these minerals occur as accessory in Granites, Syenites,

    Pegmatites,, Mica schists and Gneisses.

    Uses: some of the minerals are used as gemstone. The main producers are

    Brazil, Russia, Madagascar, United States.

    Si : O :: 3 : 9 Si : O :: 4 : 12 Si : O :: 6 : 18

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    5. PHYLLOSILICATES (SHEET STRUCTURES): These are also called sheet

    silicates. They possess the SiO4 sheet structure resulting in more growth

    along two directions of a mineral. Eg: Mica family, Chlorite family , Talc,

    Serpentine, Kaolinite. (Si : O : : 2 : 5) or (Si : O : : 4 : 10)

    Mica Family: MICA is the family name of some silicate minerals. These are

    silicates of aluminum, potassium together with magnesium. Some varieties

    contain sodium, lithium or titanium.

    The hydroxyl radical is always present and is commonly replaced partially by

    Fluorine. Hence, all mica minerals possess ( Al Si3) O10 (OH,F)2 as a common

    radical. Micas may be divided into : 1) Muscovite group & 2) Biotite group.

    Muscovite group Composition Usual name

    Muscovite K Al2(Al Si3) O10 (OHF)2 Potassium mica

    Paragonite Na Al2(Al Si3) O10 (OHF)2 Sodium micaLepidolite K (Al Li)3 (Al Si3) O10 (OHF)2 Lithium-pot mica

    Biotite group Composition

    Biotite K (Mg,Fe)3(Al Si3) O10 (OHF)2 Iron-mag mica / black mica

    Phlogophite K (Mg)3 (Al Si3) O10 (OHF)2 Magnesium mica

    Zinnwaldite K (Li Fe Al) (Al Si3)O10 (OHF)2 Lithium mica

    Glauconite K (Fe Al)2 (Si Al)4 O10 (OH)2

    Margarite Ca Al2 (Si2Al2) O10 (OH)2

    Atomic structure: all micas are phyllosilicates ie in their atomic structure SiO4

    tetrahedra are arranged in sheet pattern ( growth in two dimensions).

    Varieties: when thin mica layers are punched by a steel rod, a small six-rayed

    figure known as a percussion figure appears.

    Sericite: is a fine grained muscovite found in Gneisses and Schists

    Illite: is a clay mica found in sedimentary rocks.

    Mineral Occurrence

    Muscovite Found as accessory mineral in acid ig rocks such as Granites

    and Pegmatites. In metamorphic rocks of Gneisses & mica-schists.Biotite Igneous rocks such as Granites, Diorites; Gabbros. Also in Biotite

    gneisses; biotite schists; biotite hornfels.

    Phlogophite Found in crystalline limestones and peridotites.

    Lepidolite In Pegmatites.

    Uses: Muscovite used to be to cover lanthorns in electrical industry as an

    insulating material. In the manufacture of rubber tyres; powdered mica is used

    to give the frost effect on Christmas cards.

    Lepidolite is mined as an ore of lithium & used in lithium batteries. Phlogophite

    mica is superior to muscovite mica

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    Chlorite Family

    Generally chlorite is considered as Hydrous silicates of aluminum, iron and

    magnesium. Chlorite is a green coloured mineral. Chlorite resembles to some

    extent biotite (mica ) in physical properties but has no alkalies..

    Composition: the formula for chlorite is (Mg Fe)5 (Al Si3) O10(OH)8 .

    Atomic structure: This is a phyllosilicate with silicon oxygen ratio of 4 : 10.

    Chlorite is formed as a product of alteration of mafic minerals such as biotite

    or hornblende.

    Occurrence: chlorite occurs in chlorite schists and phyllite. It also occurs as

    amygdale.

    Varieties: Clinochlore ; penninite; ripidolite.

    Talc

    Talc is a hydrous magnesium silicate. Its chemical composition is

    Mg3(SiO3)4 H2O containing 63.5% of SiO2; 31.7% of MgO and 4.7% of H2O .

    Properties: having a good lustre and high lubricating power, particularly for oil

    and grease absorption, high fusibility very low shrinkage value. It has a low

    electrical and thermal conductivity and a good resistance to heat shock.

    Atomic structure: Talc is a phyllosilicate with a Si: O ratio of 4 : 10 . It is a

    metamorphic mineral and formed due to alteration of magnesium - bearing rocks

    like peridotites; dolomites; gabbros.

    Varieties: Steatiteor soapstone is a massive variety of Talc, mostly white or

    grey or pale green in color. Potstone is an impure massive talc, green in

    color or brownish black in color. French chalk is a steatite used by tailors for

    marking on clothes.

    TALC DEPOSITS: Bihar; UP; AP ; Tamil Nadu; Rajasthan M.P; Maharashtra;Karnataka are producing talc / steatite deposits.

    Uses: as a filler for paints, paper, rubber , cosmetics, and textiles ;

    removing grease from clothes;

    in leather making; talcum powder ;

    in switch boards, in lab table tops.

    50% used in paper industry; 15% pesticide industry; 3% talcum powder industry

    and remaining in textile, ceramics; rubber industry etc..

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    6. TECTO SILICATES ( Frame work structures ): In this group, SiO4

    tetrahedra occur in a three dimensional framework, resulting equidimensional

    growth of a mineral. (Si : O : : 1 : 2) or every SiO4 tetrahedron shares all of

    its corners with other tetrahedron giving a three dimensional network . In this

    framework structures, Si is generally replaced by Aluminum thus making themaluminum silicates.

    Minerals which this structure include: eg: quartz, other forms of silica (Flint ;

    Jasper; Chalcedony etc..); Feldspars family, zeolite family, feldspathoids family;

    Scapolite family.

    FELDSPARS FAMILY

    It refers to a group of different minerals which possess similar chemical

    composition, atomic structure; physical and optical properties. These are

    aluminous silicates of K. Na; Ca or Ba and may be considered as isomorphous

    compounds.

    Feldspars are sub-divided into: PLAGIOCLASE FELDSPARS and

    ALKALI FELDSPARS

    The Plagioclase feldspars may be defined as

    Feldspar group Range composition Occurrence

    Albite

    Na Al Si3O8to

    Ca Al2Si2O8

    Ab 100 - An 0 Granites; Syenites;Diorites; Rhyolites;Trachytes;Gabbros;Sandstones;Schists &Gneisses;

    Oligoclase Ab 90An 10

    Andesite Ab 70 - An 30

    Labradorite Ab 50 - An 50

    Bytownite Ab 30An 70

    Anorthite Ab 10 - An 90

    Uses: Feldspars are used in the manufacture of Porcelain; Pottery; glazes on

    earthware; Sanitary ware; in the manufacture of glass and ceramic industries.

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    FORMS OF SILICA ( QUARTZ; FLINT; JASPER )

    The forms of silica, including the hydrated forms can be grouped as:

    Silica occurs in nature as crystalline ( eg: Quartz; Tridymite; Cristobalite )

    as cryptocrystalline ( eg: chalcedony; Flint; Chert; Jasper; Agate )

    as Hydrous / amorphous forms ( eg: opal )

    QUARTZ: Next to feldspars and mafic minerals, quartz is the most

    common rock forming mineral. It is SiO2 in composition and may be treated

    as an oxide or as a silicate. Structurally, it is a tectosilicate ie; in its atomic

    structure, the SiO4 tetrahedra are arranged in a three dimensional network

    pattern.

    Quartz, Tridymite and Crystabalite are important crystalline forms of silica withSiO2 composition but possess different physical properties and hence these

    are called POLYMORPHS.

    Varieties of Quartz:

    Rock crystal: Transparent form of quartz and purest.

    Amethyst: Purple / violet colored; transparent form of quartz

    Rose quartz: Pale pink / rose colored variety of quartz

    Smoky quartz: smoky yellow / brown color of quartz

    Milky quartz milky white in color due to a large no. of mica cavities

    Ferruginous quartz: contains iron oxides which impart reddish color

    Uses: employed in jewellery ( eg: amethyst ); Making spectacle glasses;

    Sand papers; toothpaste; Pottery; silica bricks.

    Depend on its piezoelectric properties, a certain type of quartz is used to

    control the frequency of radio-circuits.

    FLINT: It is a compact cryptocrystalline silica of a black color or various shades

    of grey occur as irregular nodules. Flint breaks with a well marked conchoidal

    fracture and affords sharp cutting edges.

    Flint was extensively used by prehistoric man for the fabrication of weapons,

    chisels.. Flint generates sparks when struck with steel . Flint is used in tube

    mills; pottery industry; for road making and building properties. Flint nodules

    occur in limestone formations in North Wales.

    JASPER: it is an opaque form of silica, usually of red, brown yellow color and

    rarely green. Egyptian or Ribbon Jasper are beautifully banded with different

    shades of brown. Porcelain Jasper is merely clay altered by contact with a hotigneous rocks.

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    CALCIUM MINERALS:

    Calcium doesnt occur in the free state but its compounds are extremely

    abundant. Calcium occurs in limestone as CaCO3. Calcium also enters into

    the composition of many rock forming silicates such as :Anorthite ( feldspar group ) .. Ca Al2Si2O8 and in

    Pyroxenes; amphiboles; garnets; scapolites; epidotes; zeolites and wollastonites.

    Calcite is a non-silicate mineral and of great economic value. The following are

    the important non-silicate calcium minerals:

    Mineral composition Class

    Calcite Ca CO3

    CarbonatesAragonite Ca CO3

    Siderite Fe CO3

    Dolomite Ca Mg (CO3)2Anhydrite Ca SO4

    SulphatesGypsum Ca SO4 2 H2O

    Glauberite Na2Ca (SO4)2

    Apatite Ca5 (F, Cl) ( PO4)3 Phosphates

    Fluorspar Ca F2 Fluorides

    Ulexite Na Ca B5O98 H2O

    BoratesColemanite Ca2B6 O11 5 H2O

    POLYMORPHISM: Aragonite and calcite are having the same chemical

    composition but differ in physical properties.

    Varieties:

    Nail - head spar crystals showing combination of flat rhombohedron and prism.

    Ice land spar is a fibrous form of calcite whereas Aphrite & Argentine are

    unimportant varieties of calcite.

    Stalactites are pendent columns formed by the dripping of water charged with

    CaCO3 from the roofs of caverns in limestone rocks whereas Stalagmite, the

    surplus dripping of water gives rise to a similar deposit which forms one above

    the other on the floors of the caverns.

    Chalk, soft, white earth form of Ca CO3 and Limestones, marbles are forms

    of carbonate of lime.

    Occurrence: calcite may be either of an organic or of an inorganic and

    chemical origin.

    Uses: in the manufacture of bleaching powder; calcium carbide; in glass

    industry; in soap, paper; paint industries; in cement manufacturing ; in printingprocess; in optical apparatus etc..

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    DIFFERENT METHODS OF STUDY OF MINERALS

    According to the mineral definition, every mineral has its own chemical composition

    and atomic structureand it is unique for every mineral.This fact facilitates the study

    of mineral in different ways. Common methods of study and identification of minerals

    based on their

    (i) physical properties

    (ii) chemical properties

    (iii) optical properties and

    (iv) x-ray analysis.

    (i)Study of Phys ical propert ies: Physical properties like Color, Form, lustre,

    Hardness(resistance to scratching), Density(Specific Gravity), cleavageetc., can

    be studied with simple observations. These properties are dependent on chemical

    composition and atomic structure i.e., if the atomic structure and chemical

    composition remains the same, the resulting properties should also be similar.. This

    principle is the basis for the study of minerals.

    For example, any galenamineral irrespective of its place of occurrence, size, shape,

    association ,consistently exhibits lead grey colour, metallic shine, opaque

    character, high Sp gr (density = 7.4 7.6), tendency to break easily along three

    different directions and is scratched easily by knife. This set of physical properties is

    never exhibited by any other mineral .Therefore, if such properties are observed an

    unknown mineral it must be only galena.

    (ii) Study of Chemical compo sit ion: According to the definition, every mineral

    which is expected to have its own individual chemical composition, which is not to be

    found in any other mineral. Therefore, by chemical analysis if composition is known

    it should be possible to identify the mineral.

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    For example, if the composition of an unknown mineral is found to be lead sulphide

    (PbS), then that must be only galenabecause galena always has the composition

    lead sulphide and no other mineral has this composition.

    (iii) Study of op t ical propert ies: In this method of study, the minerals are made

    very fine (0.03 mm ) and fixed over glass slide by means canadabalsam such

    skillfully prepared slides are called thin sections. They are studied under

    petrological microscope.Different optical properties such as interference colours,

    their order, interference figures, optic sign, twinning, alteration etc., are studied under

    crossed nicols with help of some other accessories, if necessary.

    The optical properties of every mineral are also distinctive and hence helpful in the

    identification of minerals. For example, quartz is characterized by: anhedral

    shape, clourless, no cleavage, transparent, low relief, non-pleochroic, grey or

    yellow, interference colours of first order, positive uniaxial interference figure,

    positive elongation, no alteration etc,.

    (iv) Study of X-ray analysis: When a beam of x-rays falls on a crystal, it is

    diffracted by the layers of the atoms within the crystal. In making an x-ray analysis of

    atomic structure of the crystal, the diffracted x-rays are allowed to fall on the on

    photographic plate and resulting photograph shows a series of spots or lines which

    form more or less symmetrical pattern. From measurements made on the

    photograph, the arrangement of the atoms in the crystal can be deduced and also

    the distances between them. The results of x-ray analysis of minerals reveal their

    atomic structure, which is distinctive, for each mineral. This enables the accurate

    identification of minerals.

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    study of physical properties of minerals

    Form:The form of mineral is defined as its shape. The external shape of mineral

    reflects the internal arrangement of atoms. When a mineral occurs as a well

    developed crystal, it is called crystallized. If the growth of the crystals is hampered

    due to interference of other crystal grains then the resulting form is called

    crystalline. When just traces of crystalline structures are present, it is called

    cryptocrystalline. Due to random network of ions or the total absence of

    crystalline structure, amorphous (or) shape less forms result. Some of important

    forms are listed below.

    S.No Name of the form Description Mineral Examples

    1. Lamellar Form Mineral appears as thin

    separable layers

    Muscovite, Biotite

    2. Tabular Form Minerals appears as slabs of

    uniform thickness

    Feldspars, Gypsum

    3. Fibrous Form Mineral appears as fine

    threads

    Asbestos

    4. Pisolitic Form Mineral appears as sphericals Bauxite

    5. Rhombic Form Rhombic shape Calcite, garnet

    6. Bladed Form Minerals appear as independent

    blade or lath-shaped grains

    Kyanite

    7. Granular Form innumerable equidimensional grains

    of coarse/medium/fine size

    Chromite, graphite,

    Magnetite

    8. Reni Form Kidney-shaped Hematite

    9. Prismatic Form Elongated crystals Olivine, Augite10. Spongy Form Porous Pyrolusite, Bauxite

    11. Cubic Form Geometrical Shapes Garnet, Pyrite, Galena

    12. Massive Form No definite shape Graphite, Olivine, Quartz,

    haematite, Magnesite,

    Jasper, Pyrolusite

    13. Nodular Form Irregularly shaped compact

    bodies with curved surfaces

    Flint

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    Color: Minerals show great variety of colors and can be identified by their color.

    Color wise the minerals are of two types (i) Dark colored minerals and (ii) Light

    colored minerals. Mineral colors are generally related to the spatial arrangement of

    the constituent atoms or the impurities present in the minerals or all of these.

    For example: (i)The color related to atomic structure. Diamond is colorless and

    transparent where as Graphite is black and opaque even though both contain

    carbon. (ii) The color related to impurities: Generally pure quartz colorless and

    transparent. But commonly due to impurities it shows colors such as pink, purple etc.

    Mineral Color Mineral Color

    Calcite Colorless / white / red / grey / yellow

    Feldspar White / grey / red / green / dirty whiteQuartz Colorless / white / green / violet / grey / yellow / pink

    hornblende Dark green Augite Greenish black

    ruby Red biotite Black, greenish black

    Pyrite Brass yellow Chalcopyrite Golden yellow

    Emerald Green Chlorite Grassy green

    graphite Shining black Coal Black

    barytes White / pale grey gypsum Colorless / white

    galena Dark lead grey Haematite Dark steel grey

    Microcline White/pink/green kyanite Blue

    Chromite Black magnetite Black

    Sapphire Blue Muscovite Silver white

    Malachite Dark green Olivine Olivine green

    orthoclase White / red plagioclase Grey / white

    Garnet red talc White/yellow

    opal Milky white Tourmaline Jet black

    Streak: The streak of mineral is color of its powder. Many minerals exhibit a

    different color in the powder form compared to form of mass. The powder of themineral is obtained either by scratching the mineral with a pen knife or rubbing it

    across piece of unglazed porcelain plate called streak plate. Most transparent

    minerals show a white streak. colored minerals show a dark color streak of

    the mineral. Sometimes the streak is altogether different in color from the color of

    the mineral.

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    S.No Streak min erals

    1 Dark brown, black Pyrite, magnetite, chromite, Pyrolusite, biotite, graphite.

    2 Bluish black Pyrolusite.,

    3 Cherry red haematite

    4 Dark grey galena

    5 white Calcite, jasper, olivine, muscovite, asbestos, Kyanite, garnet,

    talc, calcite, Magnesite,

    6 colorless quartz

    7 White to grey Augite, biotite,

    8 Grey to greenish grey Hornblende,

    9 Silver white Muscovite

    10 Greenish black Biotite, pyrite,

    11 Red or reddish brown Haematite,

    Lust re: Lustre is the nature of shining on the surface of the mineral under reflected

    light. It varies considerably depending upon the amount and type of light reflected.

    Based on the type of shining, lustres are grouped as metallic and non-metallic.

    Metallic lustre is the type of shining that appears on the surface of the metal. Non-

    metallic lustres are named considering the type of shining that appears in some

    common materials. Some important non-metallic lustres that are observed mainly in

    rock-forming minerals are:

    S.No Non-metallic Lustre Description Minerals

    1. Vitreous lustre Shining like a glass Quartz, Calcite, Feldspar

    2. Subvitreous lustre Subvitreous lustre is similar to

    vitreous lustre but with less

    shining

    Pyroxenes (augite)

    3. Pearly lustre Shining like pearl Talc, Muscovite(mica)

    4. Silky lustre Shining like silk Asbestos

    5. Resinous lustre Shining like resin Opal, Agate

    6. Greasy lustre Shining like grease Graphite, Serpentine

    7. Adamantine lustre Shining like diamond Garnet, Diamond

    8. Earthy or Dull lustre No shining like earth or chalk Magnesite, Bauxite

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    Cleavage: The definite direction or plane along which a mineral tends to breakeasily is called the cleavage of that mineral. Crystallized and crystalline mineralscan have cleavage. Amorphous minerals do not show cleavage. Cleavage, ifpresent , occurs as innumerable planes along which mineral is equally weak. Henceall such parallel planes of weakness are referred to as a set.

    Depending upon their atomic structure, crystalline minerals will have 1 set ofcleavage (or) 2 sets (or) 3 sets (or) 4 sets (or) 6 sets of cleavages (or) no cleavage.

    Since atomic structure of a mineral is definite, the cleavage character of themineral will also be definite. Depending upon the degree of perfection, cleavagemay be described as perfect or eminent or excellent (mica) , good (calcite) ,imperfect or poor or indistinct (apatite).

    S.No cleavage Sets Minerals

    1 None Quartz, Flint, Jasper, Olivine, garnet, haematite,

    2 indistinct Pyrolusite, Graphite, apatite

    5 Present 1 mica, chlorite, talc, Asbestos

    6 perfect 3 Calcite, Magnesite, galena

    7 perfect 2 Feldspars, hornblende, Kyanite, augite

    Fracture: Fracture is the nature of randomly broken surface of mineral. Based on

    the nature of a broken surface, fractures are described as even fracture, uneven

    fracture, hackly fracture, and conchoidal fracture.

    S.No Name of fracture Description Minerals example

    1. Even Fracture If the broken surface of a

    mineral is plain and

    smooth, it is called even

    fracture

    Magnesite, Chalk

    2. Uneven Fracture If the broken surface is

    rough and irregular

    Augite, hornblende, mica, chlorite, talc,

    pyrite, haematite, magnetite, Pyrolusite,

    graphite, bauxite.

    3. Hackly Fracture If the broken surface is

    very irregular like the end

    of a broken stick

    Asbestos, Kyanite, chlorite,

    4 Conchoidal

    Fracture

    If the broken surface is

    smooth and curved

    Agate, Flint, Jasper, galena, bauxite.

    5 Even to uneven Olivine, Magnesite

    6 Conchoidal to sub-

    conchoidal

    Garnet,

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    Tenacity: The tenacity is a measure of the cohesiveness of minerals as shown by its

    resistance to breaking, crushing or other deformation methods. The different kinds of

    tenacity are classified as follows

    (i) Brittle: Theminerals breaks into powder

    (ii) Malleable: The minerals be beaten into sheets

    (iii) Ductile: The mineral can be drawn into thin wires

    (iv)Sectile: The mineral can be cut into thin sheets

    (v) Elastic: The minerals bend on the application of pressure but regains the

    original shape when the pressure is released.

    Hardness:Hardness may be defined as the resistance offered by the mineral to

    abrasion or scratching.

    For example, if mineral specimen is muscovite (mica), when it is tested on the mohs

    scale of hardness, it should not scratched by gypsum but by calcite. The

    composition of the mineral appears to have less influence over hardness.

    For example, graphite and diamond which possess the same composition, but

    different atomic structures, represent nearly two extremes of the hardness in the

    mineral kingdom i.e. graphite is extremely soft and diamond is extremely hard.

    Mohs Scale of Hardness: In 1882 an Australian mineralogist, Mohs proposed a

    relative scale for hardness of minerals. The standard set of ten reference minerals

    used to determine the hardness of any unknown mineral is called Mohs scale of

    hardness. The actual minerals of the set and their hardness are as follows:

    Talc = 1;

    Gypsum = 2;

    Calcite = 3;

    Fluorite = 4;

    Apatite = 5;

    Feldspar = 6;

    Quartz = 7;

    Topaz = 8;

    Corundum = 9;

    Diamond = 10;

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    Thus Talc is the least hard mineral and Diamond is the most hard mineral. The

    relative hardness of an unknown mineral is determined by scratching it with the

    Mohs scale of hardness starting with Talc and followed by minerals of increasing

    hardness. Common minerals like finger nail (H = 2.5) , a copper coin (H=3.5), a

    broken glass piece (H=5.5) and pen knife (H=6.5) may be used to fix the lower limit.

    Specif ic Gravity ( density ) : Specific gravity of mineral depends on their chemical

    composition. and atomic structure. The specific gravity of a mineral is the weight

    of it to the weight of an equal volume of water. In the laboratory, specific gravity

    of minerals is determined using either Walkers steel yard or Jollys spring balance.

    In determining specific gravity care should be taken to select only fresh (ie un

    weathered ) minerals free from inclusions, impurities etc,.

    For routine identification of minerals based on physical properties, determination of

    actual specific gravity is tedious and unnecessary because most of the rock-

    forming minerals have specific gravity range of 2.5 to 3.5, while common ore

    minerals like magnetite, hematite, ilmenite, galena, pyrite, Pyrolusite and

    Psilomelane, have specific gravity over 3.5. Only few minerals have a specific gravity

    less than 2.5. Thus based on this range of specific gravity of minerals, the density

    character of minerals may be described as high, medium or low.

    The medium density refers to the common rock-forming minerals and higher density

    refers to the common ore minerals.

    Sp. Gravity Minerals

    Low Density < 2.5 Talc, graphite,

    Medium Density 2.5 to 3.5 Feldspars, quartz, flint, jasper, olivine,

    augite, hornblende, mica, chlorite,

    asbestos, calcite, Magnesite, bauxite

    High Density > 3.5 Kyanite, garnet, pyrite, haematite,

    magnetite, chromite, galena, Pyrolusite,

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    Transparencytranslucency:

    A mineral is transparent when the outlines of objects seen through it appear

    sharp and distinct. Eg: quartz transparent

    Selenite transparentFluorite ; Topaz sub-transparent

    A mineral which, though capable of transmitting light, cannot be seen through

    is translucent.

    When no light is transmitted the mineral is opaque.

    PhosphorescenceFluorescence:

    Phosphorescence is the property possessed by some substances of emitting

    light after having been subjected to certain conditions such as heating, rubbing

    or exposure to electric or UV light.

    Eg: pieces of quartz when rubbed together in a dark room emit a

    phosphorescent light. Diamond, ruby etc when exposure to x-rays show

    phosphorescent property.

    Some minerals such as fluorspar emit light when exposed to certain electrical

    radiations ( means giving off a certain kind of light ) is called as Fluorescence.

    Depending upon certain senses taste; odour, feel etc

    TASTE:

    When the minerals are soluble in water, generally possess a characteristic

    taste which may be designated as follows:

    Taste Result

    Saline The taste of common salt , eg: halite

    Alkaline That of potash & soda

    Acidic / sour The sour taste of H2SO4

    Cool The taste of potassium chlorite

    Sweetish astringent That of alum

    Bitter That of Epsom salt

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    ODOUR: Some minerals have characteristic odours when struck, rubbed,

    breathed, heated etc terms used are::

    Odour Result on smell

    Alliaceous Garlic odour when arsenic compounds are heated .eg: arsenopyrite, orpiment, realgar

    Horse-radish odour The odour of decaying horse radish when seleniumcompounds are heated

    Sulphurous The odour of burning sulphur when sulphides heated

    Foetid The odour of rotten eggs given by heating

    Clayey The odour of clay. Eg: kaolin

    FEEL: Rough feeling of touch. Eg chalk

    Depending upon the state of aggregation. Gases & liquidsForm

    Hardness

    Tenacity

    Fracture

    Cleavage

    Gases & liquids

    O2; N2; CO2 are examples for natural gases

    H2O ; Hg ; HYDRO-CARBONS are examples for natural liquids.

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    MODE OF FORMATION OF MINERALS

    Minerals are the products of natural physic chemical processes and the

    conditions in which they originate are various. The conditions include the

    temperature, pressure and the interaction of minerals with country rocks.

    Since, minerals are hard crystalline substances, their origin is restricted

    From its liquid into its solid form eg: rock salt

    From its gaseous into its solid form eg: sassoline, cinnabar, NH4Cl

    From one hard form into another.

    The crystallization of HALITE (Rock salt / common salt ) during the evaporation of

    sea water serve as a good example for the formation of minerals from solutions

    The formation of Ammonium Chloride ( NH4Cl );

    sassoline (H3BO3 ) or Native boric acid;

    Cinnabar (HgS) ie mercury sulphide etc

    clearly indicates the emergence of minerals from a gaseous phase.

    The formation of minerals during the transition from one solid state into

    another solid state is typical of the process of RECRYSTALLIZATION;

    METAMORPHISM & METASOMATISM.

    Eg: Limestone is transformed into marble

    Quartz in sandstone becomes into quartziteClay changes into Phyllites & mica schists.

    The majority of the minerals in the earths crust have been formed by

    crystallization of molten melt ie magma. It is estimated that 95% of the earths

    crust is composed of igneous rocks which were resulted from solidification of

    magma. The chief modes of formation of minerals are .

    From Fusion ( solidification from fused rock material ie magma )

    From solution ( crystallization from a solution )

    From Vapour ( crystallization from a gas )

    Formation of minerals from Fusion: An igneous magma ( complex solution )

    in which the various elements present are free to circulate under the proper

    conditions to form mineral molecules.

    The composition of the magma determine the character of the minerals. The

    elements O, Si, Al, Fe, Mg, Ca, Na, Na, K etc occur in varying proportions in

    igneous magmas.

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    Eg: quartz, feldspars, olivine, Enstatite, hypersthenes, Augite silicates

    Hornblende, biotite, muscovite

    Apatite, monazite .. PhosphatesMagnetite, ilmenite, chromite oxidesPyrite, pyrrhotite .. sulphides

    Platinum, diamond . Elements

    Formation of minerals from vapours:

    The formation of minerals from vapours is confined such volcanic regions where

    mineral gases are discharged from fumeroles.

    Minerals deposited in this way include sulphur, Tellurium, Arsenic sulphides,

    boric acid, chlorides etc

    Eg: quartz, opal, zeolites . SilicatesGypsum sulphatesHaematite, magnetite oxidesHalite halidesPyrite, cinnabar, stibnite sulphidesSulphur ,, elements

    Formation of minerals from solutions : By the evaporation of saline water

    (sea water / salt lakes) causing certain mineral deposits.

    Eg: carbonates of lime ( CaCO3) and magnesia ( MgCO3)Calcium sulphate ( CaSO4) and Sodium Chloride ( NaCl)Sodium Sulphate ( NaSO4) and Potassium Chloride ( KCl)

    The factors of concentration, temperature, proportion of various constituents in

    the solution control the character of the minerals formed.

    Eg: Quartz, feldspars, muscovite, chlorite, hornblende,Tourmaline, zeolites, topaz silicates

    Barytes .. sulphatesCalcite, Magnesite . CarbonatesMagnetite, haematite, rutile, Brookite oxidesFluorite .. halidesGalena, pyrite, Cinnabar .. sulphidesGold, silver, arsenic, bismuth . Elements

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    Physical properties of minerals

    Form:The form of mineral is defined as its shape. The external shape of mineral reflects the

    internal arrangement of atoms. When a mineral occurs as a well developed crystal, it is

    called crystallized. If the growth of the crystals is hampered due to interference of other

    crystal grains then the resulting form is called crystalline. When just traces of crystalline

    structures are present, it is called cryptocrystalline. Due to random network of ions or the

    total absence of crystalline structure, amorphous (or) shape lessforms result. Some of

    important forms are listed below.

    S.No Name of the form Description Mineral Examples

    1. Lamellar Form Mineral appears as thin

    separable layers

    Muscovite, Biotite

    2. Tabular Form Minerals appears as slabs of

    uniform thickness

    Feldspars, Gypsum

    3. Fibrous Form Mineral appears as fine

    threads

    Asbestos

    4. Pisolitic Form Mineral appears as sphericals Bauxite

    5. Rhombic Form Rhombic shape Calcite, garnet6. Bladed Form Minerals appear as independent

    blade or lath-shaped grains

    Kyanite

    7. Granular Form innumerable equidimensional grains

    of coarse/medium/fine size

    Chromite, graphite,

    Magnetite

    8. Reni Form Kidney-shaped Hematite

    9. Prismatic Form Elongated crystals Olivine, Augite

    10. Spongy Form Porous Pyrolusite, Bauxite

    11. Cubic Form Geometrical Shapes Garnet, Pyrite, Galena

    12. Massive Form No definite shape Graphite, Olivine, Quartz,

    haematite, Magnesite,

    Jasper, Pyrolusite

    13. Nodular Form Irregularly shaped compact

    bodies with curved surfaces

    Flint

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    Color: Minerals show great variety of colors and can be identified by their color.

    Color wise the minerals are of two types (i) Dark colored minerals and (ii) Light

    colored minerals. Mineral colors are generally related to the spatial arrangement of

    the constituent atoms or the impurities present in the minerals or all of these.

    For example: (i)The color related to atomic structure. Diamond is colorless and transparent

    where as Graphite is black and opaque even though both contain carbon.

    (ii) The color related to impurities: Generally pure quartz colorless and transparent. But

    commonly due to impurities it shows colors such as pink, purple etc.

    Streak: The streak of mineral is color of its powder. Many minerals exhibit a different color

    in the powder form compared to form of mass. The powder of the mineral is obtained either

    by scratching the mineral with a pen knife or rubbing it across piece of unglazed porcelain

    plate called streak plate. Most transparent minerals show a white streak. colored

    minerals show a dark color streak of the mineral. Sometimes the streak is altogether

    different in color from the color of the mineral.

    S.No Streak mi nerals

    1 Dark brown, black Pyrite, magnetite, chromite, Pyrolusite, biotite, graphite.

    2 Bluish black Pyrolusite.,

    3 Cherry red haematite

    4 Dark grey galena

    5 white Calcite, jasper, olivine, muscovite, asbestos, Kyanite,

    garnet, talc, calcite, Magnesite,

    6 colorless quartz

    7 White to grey Augite, biotite,

    8 Grey to greenish grey Hornblende,

    9 Silver white Muscovite

    10 Greenish black Biotite, pyrite,

    11 Red or reddish brown Haematite,

    Lust re: Lustre is the nature of shining on the surface of the mineral under reflectedlight. It varies considerably depending upon the amount and type of light reflected.

    Based on the type of shining, lustres are grouped as metallic and non-metallic.Metallic lustre is the type of shining that appears on the surface of the metal. Non-metallic lustres are named considering the type of shining that appears in some

    common materials. Some important non-metallic lustres that are observed mainly inrock-forming minerals are:

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    S.No Non-metallic Lustre Description Minerals

    1. Vitreous lustre Shining like a glass Quartz, Calcite,

    Feldspar

    2. Subvitreous lustre Subvitreous lustre is similar

    to vitreous lustre but with

    less shining

    Pyroxenes (augite)

    3. Pearly lustre Shining like pearl Talc, Muscovite(mica)

    4. Silky lustre Shining like silk Asbestos

    5. Resinous lustre Shining like resin Opal, Agate

    6. Greasy lustre Shining like grease Graphite, Serpentine

    7. Adamantine lustre Shining like diamond Garnet, Diamond

    8. Earthy or Dull lustre No shining like earth or chalk Magnesite, Bauxite

    Cleavage: The definite direction or plane along which a mineral tends to break

    easily is called the cleavage of that mineral. Crystallized and crystalline minerals

    can have cleavage. Amorphous minerals do not show cleavage. Cleavage, if

    present , occurs as innumerable planes along which mineral is equally weak. Hence

    all such parallel planes of weakness are referred to as a set.

    Depending upon their atomic structure, crystalline minerals will have 1 set of

    cleavage (or) 2 sets (or) 3 sets (or) 4 sets (or) 6 sets of cleavages (or) no cleavage.

    Since atomic structure of a mineral is definite, the cleavage character of the

    mineral will also be definite. Depending upon the degree of perfection, cleavage

    may be described as perfect or eminent or excellent (mica) , good (calcite) ,

    imperfect or poor or indistinct (apatite).

    S.No cleavage Sets Minerals

    1 None Quartz, Flint, Jasper, Olivine, garnet, haematite,

    2 indistinct Pyrolusite, Graphite, apatite

    5 Present 1 mica, chlorite, talc, Asbestos

    6 perfect 3 Calcite, Magnesite, galena

    7 perfect 2 Feldspars, hornblende, Kyanite, augite

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    Fracture: Fracture is the nature of randomly broken surface of mineral. Based on

    the nature of a broken surface, fractures are described as even fracture, uneven

    fracture, hackly fracture, and conchoidal fracture.

    S.No Name of fracture Description Minerals example

    1. Even Fracture If the broken surface

    of a mineral is plain

    and smooth, it is

    called even fracture

    Magnesite, Chalk

    2. Uneven Fracture If the broken surface

    is rough and

    irregular

    Augite, hornblende, mica,

    chlorite, talc, pyrite, haematite,

    magnetite, Pyrolusite, graphite,

    bauxite.

    3. Hackly Fracture If the broken surface

    is very irregular like

    the end of a broken

    stick

    Asbestos, Kyanite, chlorite,

    4 Conchoidal

    Fracture

    If the broken surface

    is smooth andcurved

    Agate, Flint, Jasper, galena,

    bauxite.

    5 Even to uneven Olivine, Magnesite

    6 Conchoidal to

    sub-conchoidal

    Garnet,

    Tenacity: The tenacity is a measure of the cohesiveness of minerals as shown by its

    resistance to breaking, crushing or other deformation methods. The different kinds of

    tenacity are classified as follows

    (vi)Brittle: Theminerals breaks into powder

    (vii) Malleable: The minerals be beaten into sheets

    (viii) Ductile: The mineral can be drawn into thin wires

    (ix)Sectile: The mineral can be cut into thin sheets

    (x) Elastic: The minerals bend on the application of pressure but regains the

    original shape when the pressure is released.

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    Hardness: Hardness may be defined as the resistance offered by the mineral to

    abrasion or scratching.

    For example, if mineral specimen is muscovite (mica), when it is tested on the mohs scale

    of hardness, it should not scratched by gypsum but by calcite. The composition of themineral appears to have less influence over hardness.

    For example, graphite and diamond which possess the same composition, but different

    atomic structures, represent nearly two extremes of the hardness in the mineral kingdom i.e.

    graphite is extremely soft and diamond is extremely hard.

    Mohs Scale of Hardness: In 1882 an Australian mineralogist, Mohs proposed a relative

    scale for hardness of minerals. The standard set of ten reference minerals used to determine

    the hardness of any unknown mineral is called Mohs scale of hardness. The actual minerals

    of the set and their hardness are as follows:

    Talc = 1;

    Gypsum = 2;

    Calcite = 3;

    Fluorite = 4;Apatite = 5;

    Feldspar = 6;

    Quartz = 7;

    Topaz = 8;

    Corundum = 9;Diamond = 10;

    Thus Talc is the least hard mineral and Diamond is the most hard mineral. The

    relative hardness of an unknown mineral is determined by scratching it with the

    Mohs scale of hardness starting with Talc and followed by minerals of increasing

    hardness. Common minerals like finger nail (H = 2.5) , a copper coin (H=3.5), a

    broken glass piece (H=5.5) and pen knife (H=6.5) may be used to fix the lower limit.

    Specif ic Gravity ( density ) : Specific gravity of mineral depends on their chemical

    composition. and atomic structure. The specific gravity of a mineral is the weight

    of it to the weight of an equal volume of water. In the laboratory, specific gravity

    of minerals is determined using either Walkers steel yard or Jollys spring balance.

    In determining specific gravity care should be taken to select only fresh (ie un

    weathered ) minerals free from inclusions, impurities etc,.

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    For routine identification of minerals based on physical properties, determination of

    actual specific gravity is tedious and unnecessary because most of the rock-

    forming minerals have specific gravity range of 2.5 to 3.5, while common ore

    minerals like magnetite, hematite, ilmenite, galena, pyrite, Pyrolusite and

    Psilomelane, have specific gravity over 3.5. Only few minerals have a specific gravity

    less than 2.5. Thus based on this range of specific gravity of minerals, the density

    character of minerals may be described as high, medium or low.

    The medium density refers to the common rock-forming minerals and higher density

    refers to the common ore minerals.

    Sp. Gravity Minerals

    Low Density < 2.5 Talc, graphite,

    Medium Density 2.5 to 3.5 Feldspars, quartz, flint, jasper, olivine,

    augite, hornblende, mica, chlorite, asbestos,

    calcite, Magnesite, bauxite

    High Density > 3.5 Kyanite, garnet, pyrite, haematite,

    magnetite, chromite, galena, Pyrolusite,

    MINERALS

    S no Mineral hardness Density (sp gr) Cleavage1 Feldspar 66.5 2.62.73 2 sets

    2 Quartz 7 2.62.7 Absent

    3 Flint 7 2.65 Absent

    4 Jasper 6.57 6.57 Absent

    5 Olivine 6.5 3.34 Absent

    6 Augite 56 56 2 sets

    7 Hornblende 56 56 2 sets

    8 Muscovite 2.53 2.82.9 1 set

    9 Biotite 2.53 2.73.3 1 set

    10 Asbestos 2.93.2 Perfect

    11 Chlorite 1.52. 5 2.73.0 1 set

    12 Kyanite 4- 5 length &

    67breadth

    3.6 - 3.7 2 sets

    13 Garnet 6.57.5 3.54.3 Absent

    14 Talc 1 2.7 1 set

    15 Calcite 3 2.7 3 sets

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    ECONOMIC MINERALS

    S no Mineral hardness Density ( sp gr) Cleavage

    1 Pyrite 67 5 2 -3 sets

    2 Haematite 56 5. 2 Absent

    3 Magnetite 56 5. 2 Absent

    4 Chromite 5.56 4.15.1 Absent

    5 Galena 2.53.0 7.5 Perfect

    6 Pyrolusite 4.55 Indistinct

    7 Graphite 12 22.3 indistinct

    8 Magnesite 45 3.03.2 3 sets

    9 Bauxite 2 - 4 23.5 Absent

    Degree of Transparency: This is also known as diaphaneity. Depending up on the

    resistance offered by the minerals to the passage of light through them, they may be

    classified as transparent, translucent and opaque. This character of a mineral depends on

    chemical composition, impurities, inclusions, weathering and also thickness.

    Rock-forming minerals usually appear to be opaque when they are thick, but lose this

    opaque character if they are made thinner. But metallic ore minerals remain mostly opaque,

    even when they are made thinner. Therefore, the distinction between a really opaque

    mineral and other not opaque minerals will help to distinguish ore minerals from rock-forming

    minerals.

    Relative advantages and disadvantages of different methods of study: Among

    different methods of study made in the identification of a mineral, definitely x-ray

    analysis is best, because it is accurate and there is no scope for wrong

    identification. But disadvantage is that for such study many facilities, a lot of

    infrastructure, costly equipment and accessories are necessary.

    The constraints, in the study by optical properties method, are (i) opaque minerals

    are not amenable for study under ordinary petrological microscopes, special

    reflective ore microscopes are needed for their study (ii) amorphous minerals, by

    virtue of their irregular arrangement, cannot be identified by optical methods. (iii)cost involved in procuring the required equipment

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    The method of chemical analysis, this is fairly good in giving correct

    identification of minerals, but the constraints are (i) impossible to identify the

    mineral exclusively based on chemical analysis (ii) cost of equipment, reagents, and

    facilities required

    Lastly coming to the method of study of minerals by physical properties, it is most

    suitablefor the following reasons

    (i) The unique advantage is that it makes possible the study of rocks or minerals

    in the field itself.

    (ii) It does not require any equipment worth mentioning.

    (iii) It does not involve the use of chemicals and it does not need additional

    facilities.

    (iv) It involves no loss or wastage

    (v) It is the quickest, simplest and least tedious method for identification of

    minerals i.e., money, energy, and time are spent to the minimum extent.

    However, the disadvantages in this method are

    (i) In some cases even slight variation in chemical composition results in

    considerable change in colour.

    (ii) Weathering alters many physical properties significantly and makes

    identification difficult.

    (iii) Further, some minerals formed under different conditions show light

    variations in physical properties.

    Polymorph ism: polymorphism is a phenomenon where by different minerals

    possessing different physical properties occur despite having the same chemical

    composition. For example: Al2SiO5 is the composition of different minerals like

    Andalusite, sillimanite and kyanite.

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    Study of physical properties of rock forming minerals: It is necessary to

    know about the common minerals which actually make up different rocks and determine their

    properties.

    Name of the Mineral: 1. Feldspars

    S No Properties Observations

    1 Form Tabular

    2 Color Pale pink, whitish blue, grayish

    3 Streak

    4 Lustre Vitreous5 Fracture Uneven

    6 Cleavage 2 sets

    7 Hardness 66.5

    8 Density (Sp gravity) 2.62.73

    9 Varieties Plagioclase feldspars include:

    ALBITE; OLIGOCLASE ANDESINE

    LABRADORITE BYTOWNITE ANORTHITE.

    Potash feldspars include:

    Hyalophane (KAlSi3O8)Orthoclase (KAlSi3O8)Microcline (KAlSi3O8)Anorthoclase (Na KAl Si3 O8)

    10 Occurrence In granites, Syenites, diorite, rhyolite, Trachyte,

    sandstones, schists, gabbros, gneisses.

    11 Uses In the manufacture of porcelain & pottery,

    earthernware, sanitary ware, bricks manufacture,

    glasses, electronic products etc.

    12 Chemical composition NaAlSi3O8 to CaAl2Si2O8

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    Name of the Mineral: 2. Quartz

    S No Properties Observations

    1 Form Massive, crystals

    2 Color Quartz occurs in different colors. Common colors

    are white, grey, purple, brown, pink etc

    3 Streak Colorless ( harder than streak plate )

    4 Lustre Vitreous

    5 Fracture Conchoidal

    6 Cleavage Absent

    7 Hardness 7

    8 Density (Sp gravity) 2.62.7

    9 Varieties Flint, Jasper, Amethyst (purple or violet color), Opal,

    rose quartz ( pale pink color). Milky quartz ( milky

    white in color ) .

    10 Occurrence Occurs in almost igneous( granites, rhyolites),

    sedimentary (sandstones) and metamorphic rocks (

    quartzites ).

    11 Uses Glass making, optical materials, polishing / grinding

    compounds, components in electronic products,

    12 Chemical composition SiO2

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    Name of the Mineral: 3. Flint

    S No Properties Observations

    1 Form Irregular nodules, massive

    2 Color Grey, brownish, black

    3 Streak Colorless ( harder than streak plate )

    4 Lustre Resinous

    5 Fracture Conchoidal

    6 Cleavage Absent

    7 Hardness 7

    8 Density (Sp gravity) 2.65

    9 Varieties Hornstone, Chert

    10 Occurrence In sedimentary rocks such as Limestones

    11 Uses Used in tube mills, pottery industry, as road and

    building material.

    12 Chemical composition SiO2

    Name of the Mineral: 4. Jasper

    S No Properties Observations

    1 Form Massive

    2 Color Red, Grey, brown

    3 Streak Colorless ( harder than streak plate )

    4 Lustre Dull, vitreous, greasy

    5 Fracture Conchoidal

    6 Cleavage Absent

    7 Hardness 6.5 - 7

    8 Density (Sp gravity) 2.572.65

    9 Varieties

    10 Occurrence In Igneous, sedimentary & metamorphic rocks

    11 Uses Ornaments, gemstones

    12 Chemical composition SiO2

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    Name of the Mineral: 5. Olivine

    S No Properties Observations

    1 Form MASSIVE or no definite shape

    2 Color OLIVE GREEN. Mg rich types are PALE whereasiron rich types are DARK COLOURED

    3 Streak WHITE

    4 Lustre VITREOUS but OFTEN DULL

    5 Fracture EVEN TO UNEVEN

    6 Cleavage ABSENT

    7 Hardness 67

    8 Density (Sp gravity) 3.24.3

    9 Varieties FORSTERITE IS MAGNESIUM OLIVINEFAYALITE IS FERROUS IRON TYPEPERIDOT is a gem variety of olivine.

    10 Occurrence IGNEOUS ROCKS such as Peridotites, Dunites,Gabbro, Basalt, Dolerites.

    11 Uses PERIDOT IS a GEM VARIETYmanufacture of REFRACTORY BRICKS

    12 Chemical composition (Mg,Fe)2SiO4

    Name of the Mineral: 6. Augite

    S No Properties Observations

    1 Form granular, prismatic crystals

    2 Color Greenish black TO Brownish black

    3 Streak WHITE TO GREY

    4 Lustre VITREOUS TO SUB VITREOUS

    5 Fracture UNEVEN

    6 Cleavage 2-SETS

    7 Hardness 56

    8 Density (Sp gravity) 3.23.5

    9 Varieties Diallage

    10 Occurrence Basalts, Andesites, Tuffs, Gabbros, Pyroxenites,Andesites

    11 Uses

    12 Chemical composition (Ca, Na) (Mg,Fe+ , Fe+3, Al) [(Si Al)2O6]

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    Name of the Mineral: 7. Hornblende

    S No Properties Observations

    1 Form GRANULAR OR PRISMATIC or AGGREGATE

    2 Color DARK GREENISH BLACK

    3 Streak GREY TO GREENISH GREY

    4 Lustre VITREOUS TO SUB VITREOUS

    5 Fracture UNEVEN

    6 Cleavage 2 sets

    7 Hardness 56

    8 Density (Sp gravity) 33.47

    9 Varieties Edenite, Paragasite

    10 Occurrence In IGNEOUS ROCKS such as Granites, Syenites, Diorites,

    Hornblendite and in METAMORPHIC ROCKS such as

    Gneisses, Schists, Amphibolites.

    11 Uses 1.DECORATION

    2.USED AS INSULATING MATERIAL

    3.USED AS ELECTRIC COMMUTATORS

    12 Chemical composition (Ca, Mg, Fe, Na, Al)7-8(Al Si)8O22(OH)2

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    Name of the Mineral: 8. Muscovite

    S No Properties Observations

    1 Form LAMELLAR (layers are separable and occurs inbook form ); some occur as flaky minerals.

    2 Color Brownish black, silver white, brownish yellow

    3 Streak white

    4 Lustre Vitreous, pearly

    5 Fracture EVEN / HACKLY

    6 Cleavage 1 set

    7 Hardness 2 - 2.5

    8 Density (Sp gravity) 2.76 - 3.0

    9 Varieties PARAGONITE- SODIUM MICALEPIDOLITE- LITHIUM MICASERICITE is a fine grained muscovite type found ingneisses and schists.Gilbertite Illite, a variety of mica is found in sedimentaryrocks

    10 Occurrence found in igneous rocks such as Granites,

    Pegmatites and Phlogophites..

    11 Uses Electrical industry,, wall finishes, thin transparent

    sheets are used as an insulator and used in circuit

    boards.

    12 Chemical composition KAl2(Si3Al)O10(OH,F)2

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    Name of the Mineral: 9. Biotite

    S No Properties Observations

    1 Form LAMELLAR (layers are separable and occurs in

    book form ); some occur as flaky minerals.

    2 Color dark brown, black, dark greenish black

    3 Streak white to gray

    4 Lustre Vitreous, pearly

    5 Fracture EVEN / HACKLY

    6 Cleavage 1 set

    7 Hardness 2.5 - 3

    8 Density (Sp gravity) 2.7 - 3.1

    9 Varieties LEPIDOMELANEPHLOGOPITE: Mg .MICAZINNWALDITE: LITHIUM MICA (pale white)

    10 Occurrence found in igneous ROCKS such as Granites,

    Diorites, Gabbros, and in metamorphic rocks viz.,

    Biotite gneisses, Schists, Hornfels.

    11 Uses 1.USED AS INSULATING MATERIAL2.USED AS ELECTRIC COMMUTATORS

    12 Chemical composition K(Mg,Fe)3(Si3Al)O10(OH,F)2

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    Name of the Mineral: 10. Asbestos

    S No Properties Observations

    1 Form Fibres / FIBROUS

    2 Color Pale green / whitish green

    3 Streak white

    4 Lustre SILKY

    5 Fracture UNEVEN TO HACKLY

    6 Cleavage Perfect

    7 Hardness 56

    8 Density (Sp gravity) 2.93.2

    9 Varieties Nephrite, Uralite

    10 Occurrence Occurs in actinolite schistose rocks

    11 Uses Fire proof fabrics, brake linings, manufacture of

    asbestos sheets, boards, roofing tiles, fire proof

    paints.

    12 Chemical composition Ca2 (Mg Fe)5 Si8O22 (OH)2

    Name of the Mineral: 11. chlorite

    S No Properties Observations

    1 Form FOLIATED

    2 Color GREEN usually dark grass green

    3 Streak

    4 Lustre Vitreous to earthy

    5 Fracture

    6 Cleavage

    7 Hardness 2.5

    8 Density (Sp gravity) 2.6 - 3.3

    9 Varieties Chamosite ( iron-rich chlorite),

    Ripidolite, Penninite, Clinochlore.

    10 Occurrence In igneous rocks due to alteration of biotite and in

    metamorphic rocks such as chlorite Phyllites,

    chlorite schists.

    11 Uses

    12 Chemical composition Mg,Fe, Al (Al, Si3) O10(OH)8

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    Name of the Mineral: 12. Kyanite

    S No Properties Observations

    1 Form Long blades, fibres

    2 Color Light blue

    3 Streak White

    4 Lustre Vitreous to pearly

    5 Fracture Uneven

    6 Cleavage 2 sets

    7 Hardness 4-5 along length and 67 along breadth

    8 Density (Sp gravity) 3.63. 7

    9 Varieties Andalusite

    10 Occurrence In Gneisses, Schists, Eclogites

    11 Uses In refractories. As heating element, in ceramic

    industry.

    12 Chemical composition Al2Si O5

    Name of the Mineral: 13. Garnet

    S No Properties Observations

    1 Form Rhombohedron / Rhombododecahedron

    2 Color Red, brownish red, pink

    3 Streak Colorless

    4 Lustre Vitreous

    5 Fracture Uneven or sub-conchoidal

    6 Cleavage Absent

    7 Hardness 6.57.5

    8 Density (Sp gravity) 3.54.39 Varieties Grossularite; Pyrope, Almandine, Spessartite,

    Andradite, Uvarovite

    10 Occurrence In Syenites and in Gneisses, schists,

    11 Uses An abrasive and as a gemstone

    12 Chemical composition (R +3, R+2 (SiO4)3 where

    R2+ = Ca, Mg, Fe, Mn) and R3+= Fe, Al, Cr, Ti

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    Name of the Mineral: 14. Talc

    S No Properties Observations

    1 Form FOLIATED

    2 Color White, green, grayish

    3 Streak White

    4 Lustre Pearly

    5 Fracture Even

    6 Cleavage 1 set

    7 Hardness 1

    8 Density (Sp gravity) 2.7

    9 Varieties Steatite, soapstone

    10 Occurrence Peridotites, Gabbros, Dolomites, Schists,

    11 Uses Talcum powder industry, paper industry, as a filler

    in pains, rubber industry, in electrical industry.

    12 Chemical composition Mg3( Si4O10) (OH)2

    Name of the Mineral: 15. Calcite

    S No Properties Observations

    1 Form Rhombic / tabular

    2 Color White

    3 Streak White

    4 Lustre Vitreous

    5 Fracture Even

    6 Cleavage 3 sets

    7 Hardness 3

    8 Density (Sp gravity) 2.719 Varieties Iceland spar

    10 Occurrence In limestones and marbles

    11 Uses In cement industry, manufacture of bleaching

    powder,, as a calcium carbide ,

    12 Chemical composition CaCO3

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    STUDY OF COMMON ECONOMIC MINERALS

    BAUXITEis an amorphous mineral which consists of the metallic elementof aluminum. Bauxite is formed under tropical weathering from different

    rocks. Such weathering results in leaching of all soluble matter and leaving

    behind enriched residues of oxides and hydroxides of aluminum , ferrous,

    ferric , manganese, titanium and silica. Aluminum is not found in a free state,

    but it is the most abundant metal in earths crust.

    Chemical composition: Bauxite, a mixture of aluminum hydroxides such as

    diaspore ( H Al O2 ), boehmite (AlO (OH) ) and gibbsite (Al ( OH)3) together with

    impurities of iron oxide, phosphorus compounds and titania. The following is the

    range of oxide percentage of bauxite:

    Al2O3 5565%

    Fe2O3 2 - 20%

    SiO2 2 - 10 %

    TiO2 13%

    H2O 1030%

    Physical Properties: mentioned separately

    Occurrence: Bauxite results from the decay and weathering of aluminum

    bearing rocks.

    Uses: For the manufacture of aluminum. Aluminum is used as abrasives; as

    refractory bricks.; in making cables ; household vessels, wrapping aluminum foil,

    cans, etc.. Owing to its low specific gravity 2.58, it is of great value in the

    manufacture of many articles .

    PYRITE :Though there are no native sulphur deposits in India, Pyriteserve the purpose of producing sulphur by eliminating sulphur from ironpyrites ( FeS2), which contains 53 % of sulphur and 47% Fe. It has a brassyellow color. Pyrrhotite, which also contains iron and sulphur, has a formulaof Fe11S12.

    Pyrite occurs as massive or lumps or as fines.

    Chemical composition: Fe S2.

    Physical Properties: mentioned separately

    Occurrence: The principal sources of pyrites and pyrrhotite in India are thesedimentary pyrite deposits of Bihar and Rajasthan. Karnataka, also producingpyrite deposits and the deposits are restricted to ultra basic igneous rocks.

    Uses: The main use of pyrite is to manufacture sulphuric acid, in the

    manufacture of phosphatic fertilizers.. Motion picture films consume a goodamount sulphuric acid.

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    GRAPHITE: Graphite is one of the principal allotropic modifications ofcarbon, the other two are coal and diamond. Carbon is known in three

    different conditions

    Transparent and crystallized as diamond, Scaly and crystalline as Graphite andAmorphous as charcoal, coal. These different forms, though chemically

    identical, vary in hardness, specific gravity and other physical properties.

    Native carbon occurs as two important minerals viz., diamond and graphite

    while amorphous carbon is coal. Again, carbon forms with oxygen and

    hydrogen many series of compounds known as the Hydrocarbons.

    The sp gravity of graphite is 2.1 and hardness varies between 1 and 2. It is

    absolutely opaque in character and resistant to heat and a very goodconductor of heat and electricity.

    Chemical composition: It is a pure carbon and sometimes contaminated

    with a small amount of silica, iron-oxides , clay etc.

    Physical Properties: mentioned separately

    Occurrence: Graphite is the stable form of carbon at a high temperature. The

    majority of graphite deposits are formed by the metamorphism of carbonaceousmatters particularly anthracite coal. .

    Graphite occurs in Bihar, Orissa, Tamil Nadu, Kerala, Rajasthan; WB; Sikkim;

    J & K; Karnataka and Andhra Pradesh. In A.P., East Godavari district ( kothala

    village ) is identified with veins in khondalites. In Bhadrachalam graphite

    deposits occur as veins in khondalites ( pulikonda area, Rachakonda area ).

    Uses: Low grade graphite is used in the paint and varnish industries whereas

    the high grade variety is used in batteries, lubricants, and brushes.

    Graphites are used for the manufacture of crucibles for melting of metals. It is

    required for lead pencil manufacturing industry. Graphite is also used for dry

    lubrication where oil or grease is harmful.

    Graphite is very much in demand for the manufacture of electric motor

    brushes. ( eg: mixy motor or generators etc..)

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    MAGNESITE : Magnesite, which is a carbonate of magnesium( MgCO3), contains about 47% of MgO and 53% of CO2. Magnesite is considered

    as an ore for the extraction of metallic magnesium.

    When Magnesite is Calcined at a temperature of 1500

    o

    C, the magnesia isconverted to a crystalline form known as Periclasewhich has a sp gravity of

    3.68.

    Chemical composition: It is a magnesium carbonate ( Mg CO3). Magnesite is

    commonly massive and fibrous, sometimes very compact.

    Physical Properties: ( mentioned separately )

    Occurrence: Economically important deposits of Magnesite occur as irregular

    veins in serpentinite rocks and it is found as alteration of serpentinite rocks.

    In India Magnesite occurs extensively in Salem district of Tamil Nadu where

    the Magnesite deposits were formed in the ultra basic rocks of chalk hills. In

    addition, Magnesite occurs in Karnataka as a decomposition product of ultra

    basic rocks.

    Uses: Magnesite required as fertilizer. It is also used as filler in paint and

    glass industries. Calcined magnesia is useful in manufacturing paper pulp

    from wood and bamboo.

    Magnesia powder is used in furnace - linings and crucibles; also employed in

    the manufacture of special cements and sugar industries.

    Name of the ECONOMIC MINERAL: 1. PYRITE

    S No Properties Observations

    1 Form Cube, Granular

    2 Color Bronze yellow

    3 Streak greenish black / brownish black

    4 Lustre metallic

    5 Fracture Conchoidal / Uneven

    6 Cleavage 3 sets

    7 Hardness 66.5

    8 Density (Sp gravity) 4.85.1

    9 Varieties Marcasite, Pyrrhotite, Pyrrhotite

    10 Occurrence Accessory mineral in IGNEOUS ROCKS

    11 Uses PRODUCTION OF sulphur and sulphuric acid

    12 Chemical composition FeS2,

    ( refer RUTLEYS elements of Mineralogyby HH Read, pp 523524)

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    Name of the ECONOMIC MINERAL: 2. HAEMATITE

    S No Properties Observations

    1 Form Massive / Rhombohedron

    2 Color Steel grey

    3 Streak Cherry red / red to reddish brown

    4 Lustre Metallic to Sub-metallic

    5 Fracture Uneven

    6 Cleavage Absent / poor

    7 Hardness 5.5 - 6.5

    8 Density (Sp gravity) 4.95.35.2

    9 Varieties Specular iron, kidney ore, Reddle, Martite

    10 Occurrence IGNEOUS,SEDIMENTARY, METAMORPHIC

    11 Uses 1. Iron ore

    2.PIGMENT

    12 Chemical composition Fe2O3,

    ( refer RUTLEYS elements of Mineralogy by HH Read, pp 518 519)

    Name of the ECONOMIC MINERAL: 3. MAGNETITE

    S No Properties Observations

    1 Form Granular / octahedral

    2 Color Iron black

    3 Streak Black

    4 Lustre Metallic to Sub-metallic

    5 Fracture Sub-conchoidal

    6 Cleavage Absent / poor

    7 Hardness 5.56.5

    8 Density (Sp gravity) 5.18

    9 Varieties

    10 Occurrence In igneous / sedimentary rocks

    11 Uses Valuable ore of iron

    12 Chemical composition Fe3O4

    ( refer RUTLEYS elements of Mineralogy by HH Read, pp 517 518)

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    Name of the ECONOMIC MINERAL: 4. CHROMITE

    S No Properties Observations

    1 Form Granular

    2 Color Black / BROWNISH BLACK

    3 Streak Brown

    4 Lustre Sub-metallic

    5 Fracture Uneven

    6 Cleavage Absent

    7 Hardness 5.5

    8 Density (Sp gravity) 4.54.8

    9 Varieties Picotite, lead chromite m

    10 Occurrence In Peridotites, Serpentinites, gabbros

    11 Uses The only source of chromium

    12 Chemical composition FeCr2O4

    ( refer RUTLEYS elements of Mineralogy by HH Read, pp 486487)

    Name of the ECONOMIC MINERAL: 5. GALENA

    S No Properties Observations

    1 Form Cube or Rectangular Blocks or octahedral

    2 Color Lead Grey

    3 Streak Lead Grey

    4 Lustre Metallic but often dull

    5 Fracture Even, sub-conchoidal

    6 Cleavage 3 sets

    7 Hardness 2.5

    8 Density (Sp gravity) 7.47.6

    9 Varieties Minium, Cerussite, Phosgenite, Leadhillite, anglesite

    10 Occurrence

    11 Uses ore of pb, cable covers, foils, lead sheets, piping,

    soldering,

    12 Chemical composition PbS

    ( refer RUTLEYS elements of Mineralogy by HH Read, pp 456 463)

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    Name of the ECONOMIC MINERAL: 8. MAGNESITE

    S No Properties Observations

    1 Form Massive, compact, crystals

    2 Color White, grayish white, yellowish, brown

    3 Streak Blacken

    4 Lustre Vitreous / dull/ earthy

    5 Fracture Conchoidal

    6 Cleavage Present but not distinct

    7 Hardness 3.54.5

    8 Density (Sp gravity) 2.83.0

    9 Varieties Broocite, Epsomite, Periclase Kieserite

    10 Occurrence As irregular veins in serpentine masses

    11 Uses To produce CO2, magnesium salts, refractorybricks, furnace linings, crucibles

    12 Chemical composition MgCO3

    ( refer RUTLEYS elements of Mineralogy by HH Read, pp 296 297)

    Name of the ECONOMIC


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