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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