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UNIT-II MINERALOGY

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UNIT-II MINERALOGY. MINERALOGY. A mineral is naturally occurring homogeneous inorganic substance having distinctive physical properties and a more or less definite chemical composition. Minerals are to a large extent the units which make up the rocks of the earths crust or the outer shell. - PowerPoint PPT Presentation
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UNIT-II MINERALOGY
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Page 1: UNIT-II MINERALOGY

UNIT-IIMINERALOGY

Page 2: UNIT-II MINERALOGY

MINERALOGY

• A mineral is naturally occurring homogeneous inorganic substance

having distinctive physical properties and a more or less definite

chemical composition.

• Minerals are to a large extent the units which make up the rocks of

the earths crust or the outer shell.

Page 3: UNIT-II MINERALOGY

MODE OF FORMATION OF MINERALS

• Three kinds of formation of minerals in nature

1. Formed from magma

2. Secondary process

3. Metamorphism

I. Directly formed from deposition of molten magma - feldspar, quartz,

pyroxenes, amphiboles, micas

II. Due to weathering, precipitation, deposition (secondary process) –

calcite, dolomite, bauxite, coal, petroleum

III. Formed under the influence of high temperatures and pressures with

and without the active involvement of chemically active solution

(metamorphism)- Garnets, chlorite, graphite

Page 4: UNIT-II MINERALOGY

CRYSTALLOGRAPHY

• Great majority of minerals when the conditions of formations are

favorable, occur in definite and characteristic geometric forms

known as crystals.

• Crystal-Greek word “Krystallos” meaning clear ice.

• The study of crystals is called as crystallography..

• “Crystals are bodies bounded by surfaces usually flat, arranged on

a definite plan which is an expression of an orderly internal

arrangement of the atoms”.

Page 5: UNIT-II MINERALOGY

CRYSTALLOGRAPHIC ARRANGEMENT

Page 6: UNIT-II MINERALOGY

SYMMETRY

• All crystals show by the arrangement of their faces a definite

symmetry which enables one to group them into different classes

• Types of symmetry

– Plane of symmetry

– Axis of symmetry

– Centre of symmetry

Page 7: UNIT-II MINERALOGY

SYMMETRY

1.PLANE OF SYMMETRYA plane of symmetry divides a crystal into two similar and similarly placed halves

2.Axis of symmetryIf a crystal on being rotated comes to occupy the same position in space more than once in a complete turn the axis about which the rotation has taken Is called as axis of symmetry

3.Centre of symmetryA crystal is said to have centre of symmetry if an imaginary line can be passed from any point on its surface through its centre and a similar point can be found on the line at an equal distance beyond the centre

Page 8: UNIT-II MINERALOGY

PHYSICAL PROPERTIES

1. Colour

2. Lustre

3. Structure

4. Hardness

5. Cleavage

6. Fracture

7. Specific gravity

8. Tenacity

9. Odour and taste

Page 9: UNIT-II MINERALOGY

Colourvery useful in identifying mineral in spite of the fact that colour is constant in most of the minerals and commonly colour is due to stain or impurities in the minerals.LustreAppearance of a fresh surface of a mineral in a ordinary reflected lightMetallic- galenaGlassy-vitreousPearly-talcStructureTerm used to denote the shape and form of minerals.1. Columnar2. Bladed3. Fibrous4. Radiated5. Lamellar6. granular

Page 10: UNIT-II MINERALOGY

HardnessResistance a mineral offers to abrasion or scratching and is measure relative to a standard scale of ten minerals known as Moh’s scale of hardnessCleavage Tendency of many crystallized minerals to break or split in certain parallel directions yielding more or less smooth surfaces known as cleavage planes.May be perfect and imperfectFractureAppearance of the broken surface of the mineral.Specific gravitySpecific gravity of a mineral is the ratio of its weight to the weight of an equal volume of water.

Page 11: UNIT-II MINERALOGY

TenacityThe resistance which the mineral offers to breaking, crushing, bending or tearing-in short its cohesiveness is known as tenacityEx Brittle, sec tile, malleable, flexible and ductileTasteA few minerals which are soluble in water have more or less characteristic tastesAcid, alkaline, astringent, bitter, cooling, pungent, saline

Page 12: UNIT-II MINERALOGY

ISOMORPHISM

• Peculiar natural phenomenon

• Minerals appear to be mixtures of two different

minerals from chemical composition.

• This type of formation is called as isomorphism

• Examples: Feldspar, pyroxene, amphiboles and garnets

Page 13: UNIT-II MINERALOGY

ROCK FORMING MINERALS• Silicate ranks first in the earths crust for rock forming minerals.

• SiO4 tetrahedron ins the fundamental unit of all silicate minerals.

STRUCTURE OF SILICATES:

1. Nesosilicates - SiO4 occurs as Independent unit E.g. garnet.

2. Sorosilicate - SiO4 occurs as pairs unit E.g. garnet.

3. Inosilicate - SiO4 occurs as chains along one direction or single chain silicates e.g. pyroxenes

4. Cyclosilicates - SiO4 occurs as ring form as 3 or 4 units called as ring silicates e.g beryl

5. Phyllosilicates - SiO4 occurs as sheets; called as sheet silicates. E.g mica, chlorite

6. Tectosilicates - SiO4 occurs as three dimensional frame work e.g quartz, feldspar

Page 14: UNIT-II MINERALOGY

MINERAL GROUP OR FAMILIES

• Some silicate minerals have similar atomic structure and

chemical composition. Such set of minerals are called as

groups or families.

Examples of some important groups of silicate minerals

1. Feldspar group

2. Pyroxene group

3. Amphibole group

4. Garnet group

Page 15: UNIT-II MINERALOGY

I. FELDSPARS

• Most abundant of all the silicate minerals.

• The name refers to a group and not a single mineral

• Make up about half the rocks of earths crust

• Form monoclinic and triclinic crystals and are aluminous silicates of K, Na or

Ca.

• Three common molecules

– Orthoclase - KAlSi3O3

– Albite - NaAlSi308

– Anorthite - CaAlSi3O8

IMPORTANT DETAILS OF ROCK FORMING MINERAL

Page 16: UNIT-II MINERALOGY

CRYSTAL SYSTEM : MONOCLINIC

Any mineral that falls under the

following specifications belongs to

the monoclinic crystal system.

Three axes, all of them are

unequal in length. Two of them

are at right angles to each other,

while the third is lies at an angle

other than 90°.

Page 17: UNIT-II MINERALOGY

CHEMICAL COMPOSITION-FELDSPAR

In chemical constitution, felspars are chiefly Alumino-silicates of sodium,

potassium and calcium with the following general formula : WZ4 O8

where W=Na ,K, Ca and Ba and Z= Si and Al .

The Si : Al shows a variation of 3:1 to 1:1 .

Some examples of chemical composition of felspar minerals are : KAlSi3O8

– NaAlSi3O8 – CaAl2Si2O8

Occurs in isomorphous series

Page 18: UNIT-II MINERALOGY

ATOMIC STRUCTURE-FELDSPAR

1. At atomic level ,the felspars shows a continuous three-dimensional

network type of structure in which SiO4 tetrahedra are linked at all the

corners, each oxygen ion being shared by two adjacent tetrahedral.

2. The SiO4 tetrahedra is accompanied by AlO4 tetrahedra so that the

feldspar are complex three dimensional framework of the above two

types of tetrahedra.

3. The resulting network is negatively charged and these negative

charges are satisfied by the presence of positively charged K, Na, Ca

and Ba.

4. The felspar group of minerals crystallize only in two crystallographic

systems Monoclinic and Triclinic.

Page 19: UNIT-II MINERALOGY

CRYSTALLIZATION

The feldsdpar group of minerals crystallize only in two crystallographic systems Monoclinic and Triclinic.

CLASSIFICATION

Chemically felspar fall into two main groups:The potash felspar The soda lime felspar .

Common members of the two groups are -

Potash felspar :

Orthoclase (KAlSi3O8), Sanidine(KAlSi3O8) and Microline (KAlSi3O8).

Soda – lime feldspar :

These are also called the plagioclase feldspars and consists of an isomorphous series of six felspar with two components: NAlSi3O8 and Ca Al2 Si2O8 as the end members.

1. Albite 4. Labradorite

2. Oligoclase 5. Bytwonite

3. Andesine 6. Anorthite

The above series is also known as Albite-Anorthite series.

Page 20: UNIT-II MINERALOGY

Crystallographically ,felspar fall in two crystal systems .

Monoclinic Feldspars

1. Orthoclase (KAlSi3O8 )

2. Sanidine (KAlSi3O8 )

Triclinic Feldspars

1. Microcline (KAlSi3O8 )

2. Albite – Anorthite series (six minerals)-(six minerals)

PHYSICAL PROPERTIES

In addition to their close relationship in chemical composition ,crystallography and atomic constitution ,felspar group of minerals exhibit a broad similarity and closeness in their physical characters as well so that differentiation of one variety from other requires very thorough, sometimes microscopic examination. Light in colour, lower specific gravity , have a double cleavage and a hardness varying between 6-6.5.

COMMON TYPE OF MINERALS

1. Orthoclase 2. Microcline 3. Albite 4. Anorthite

Page 21: UNIT-II MINERALOGY

PHYSICAL PROPERTIES-FELDSPAR

Form Tubular, mineral occurs as uniform thickness

Colour Generally white, pale grey or pale red

Streak White or pale body colour

Lustre Vitreous

Fracture Even to uneven

Cleavage Two sets one set is better developed

Hardness 6

Density Medium, 2.57

Occurrence weathering

Page 22: UNIT-II MINERALOGY

22

OrthoclaseCrystal system Monoclinic ; β=63•57•.Crystals commonly occur in prismatic

shape.

Cleavage Shows cleavage in 2 directions. The one parallel to basal pinacoid (001) is perfect. The cleavage angle is 90•.

Colour Various shades of pink and red, such as flesh red, reddish white, light pink . The transparent variety is called the Adularia .

Luster Vitreous to semiviterous.

Hardness and specific gravity

6-6.5 ; 2.56 to 2.58

Composition KAlSi3O8

Optical Optically negative (-)

Occurrence A most common and essential constituent of many igneous rocks ,especially granites .

Economic use As a ceramic material.

Varieties 1. Adularia-a transparent orthoclase.2. Sanidinc-a high temperature variety stable above 900•C

Page 23: UNIT-II MINERALOGY

23

microclineCrystal system Triclinic, resembles closely with orthoclase in crystal

habits.

Cleavage In two directions, the one parallel to basal pinacoid(001) is perfect.

Colour Similar to orthoclase. In addition , may occur as a greenish felspar,when it is called amazonite.

Streak ,hardness and specific gravity

colorless, 6-6.5,2.54 to 2.57

Composition KAlSi3O8

Optical Optically negative (-).Occurrence It occurs along with the orthoclase in granites and other

igneous rocks.

Economic use As a ceramic material and semi-precious stone (amazonite).

Varieties Anorthoclase (meaning-not orthoclase).It is a triclinic felspar containing sodium aluminum silicate.

Page 24: UNIT-II MINERALOGY

albiteCrystal system Triclinic ,it is the first member of the isomorphous

plagioclase series .

Cleavage Present in 2 directions. the one parallel to basal pinacoid (001)is perfect.

Colour Commonly whitish or pinkish white but shows shades of grey,green and blue.

Streak Colourless

Luster Vitreous to pearly.

Hardness and specific gravity 6-6.5 , 2.60-2.62

Composition Sodium aluminum silicate with NaAlSi3O8 - 100-90 % and CaAl2Si2O8 -0-10%.

Optical Optically positive(+).

Occurrence It is an essential constituent of many igneous rocks such as granite,syenites,rhyolites and dacites.

Economic use As a ceramic material.As an ornamental stone in polished form.

Page 25: UNIT-II MINERALOGY

anorthiteCrystal system Triclinic, it is the last member of the isomorphous plagioclase series.

Cleavage Present in two directions, the one parallel to basal pinacoid (001)if perfect .

Colour Generally white, may also occur in reddish and light grey shades.

Streak Colourless

Luster Semi-vitreous.

Composition CaAl2Si2O8 -100-90%

Optical Optically positive (+)

Occurrence An important constituent of many basic types of igneous rocks.

Varieties Composition of other members of plagioclase felspars has mentioned above . These maybe broadly considered the varieties of plagioclase felspars.

Page 26: UNIT-II MINERALOGY

II. QUARTZ• Composition of SiO2

• Most abundant material next to felspar• Colourless or white• Many coloured varieties are mainly due to impurities.• Three main varieties

1. Crystalline -Rock crystal, amethyst, rose quartz, milky quartz2. Crypto-crystalline -Chalcedony, carnclian3. Amorphous-opal

Mostly used for jewellery and ornamental purposes

Page 27: UNIT-II MINERALOGY

27

QUARTZCrystal system Hexagonal, (rhombohedral). Crystals common ; some

crystals weighing many tones have been reported. Twinned ,right-handed and left-handed crystals are common.

Cleavage Generally absentFracture ConchoidalColour Colourless when pure, quartz also occur in coloured

varieties :red, green , blue and mixture.Hardness 7Sp. Gravity 2.65-2.66Streak White in coloured varietiesVarieties It is a very common rock forming mineral and occurs in

numerous varieties . A few common varieties are mentioned below.

Page 28: UNIT-II MINERALOGY

Polymorphous transformationQuartz, when heated , transforms into high temperature modifications as follows: (870•C) (1470•C) (1713•C) Quartz ↔ Tridymite ↔ Cristobalite ↔ melt The variety named as QUARTZ itself has two polymorphs : 1. Α quartz, 2. β quartz. Identification of the exact type of quartz (into Αand β) requires thoroug investigations of the mode of formation of mineral as observed by its place of occurrence and also type of symmetry. Right handed and left handed quartz : When occurring, quartz may be distinguished into right handed and left handed types.Carried out on the basis of recognition of some typical faces such as trigonal, trapezohedron and dipyramid. These two faces normally occur at the edges of the prism faces, one above the another. In the left handed quartz ,these faces are located on the left side of the upper edge of the prism, whereas in the right handed quartz, these occur on the right upper edge of the crystals. Such a location of these faces in manifestation of an internal atomic arrangement in the crystal.

Page 29: UNIT-II MINERALOGY

29

• COLOURED VARIETIES :Common pure quartz is a colourless transparent mineral. Presence of even a trace of an impurity may give it a characteristic colour and hence a variety . A few common types of quartz distinguished on their basis are :1. Amethyst – purple or violet2. Smoky- dark to light brown, even black3. Milky- pure white and opaque4. Rose red – colour is attributed to presence of titanium.

Page 30: UNIT-II MINERALOGY

CRYPTOCRYSTALLINE TYPES : In many cases, crystalline of pure silica to quartz remains incomplete due to interruption in

the process for one reason to another. Silica occurring in these cryptocrystalline varieties, although close in composition and physical properties to quartz is named differently. A few common varieties of cryptocrystalline silica are as follows :

1. Chalcedony – luster ,waxy, commonly translucent, generally massive.2. Agate – often banded , opaque and massive.3. Onyx – a regularly banded agate having alternating and evenly paced layers of different

colours.4. Flint – a dull opaque variety of chalcedony breaking with characteristic conchoidal fracture.5. Jasper- a dull red, yellow,almost amorphous variety of silica.OCCURRENCE Quartz and its varieties occur in all types of rocks ;igneous, sedimentary and metamorphic. In igneous rocks, quartz makes up bulk of acidic varieties. In sedimentary rocks quartz makes up sandstones and ortho quartzites. Loose sands consist mostly of quartz grains. The metamorphic rocks like gneisses contain good proportion of quartz in some cases. A metamorphic rock named as (Para) quartzite is entirely made up of quartz.

Page 31: UNIT-II MINERALOGY

PIEZOELECTRICITYQuartz crystals have piezoelectric properties; they develop an electric potential upon

the application of mechanical stress. An early use of this property of quartz crystals was in phonograph pickups. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. The quartz clock is a familiar device using the mineral. The resonant frequency of a quartz crystal oscillator is changed by mechanically loading it, and this principle is used for very accurate measurements of very small mass changes in the quartz crystal microbalance and in thin-film thickness monitors.

Quartz scepters

Page 32: UNIT-II MINERALOGY

PHYSICAL PROPERTIES-QUARTZ

Form Granular or short prismatic

Colour Black or dark greenish black; pale colour – magnesium rich pyroxene

Streak White or pale body

Lustre Vitreous

Fracture Uneven

Cleavage Two sets od prismatic cleavage 87° and 93°

Hardness 5 to 6

Density Medium

Specific gravity 3.2 to 3.5

Page 33: UNIT-II MINERALOGY

III. PYROXENE

• Constitute important group of minerals that are generally

recognized by their stout crystals and their two cleavages

right angles to each other.

• Most pyroxenes are dark coloured

• Ca, Mg and Fe silicate composition

• Varieties

– Monoclinic pyroxene - Augite

– Orthorhombic pyroxene - Hypersthene

Page 34: UNIT-II MINERALOGY

CHEMICAL COMPOSITION

– Composition mainly consists of silicates of calcium, magnesium and

ferrous iron.

– At initial formation magnesium rich varieties

– At later stage iron rich formation

– General formula R2(AlSi)2 where R –divalent calcium, magnesium or

ferrous iron

ATOMIC STRUCTURE

– Single chain silicates

– Have 1:3 ratio of silicon and oxygen

– Mostly crystallize in the form of either orthorhombic or monoclinic

system

Page 35: UNIT-II MINERALOGY

MONOCLINIC PYROXENE- AUGITE

Page 36: UNIT-II MINERALOGY

AUGITE - DESCRIPTION

• Chemical Formula: (Ca,Na)(Mg,Fe,Al)(Al,Si)2O6

• Augite is an important rock-forming mineral, and large crystals are

fairly common.

• It is the most widespread member of the pyroxene group, and it

frequently alters to many other minerals, including Hornblende.

• Augite usually occurs in dull crystals that are ugly and uninteresting.

• The name Augite is derived from the Greek word augites,

"brightness", in reference to the bright luster this mineral

occasionally exhibits.

Page 37: UNIT-II MINERALOGY

OCCURRENCE

• Major rock forming mineral in mafic igneous rocks, ultramafic rocks and some high grade metamorphic rocks.

Page 38: UNIT-II MINERALOGY

Crystal System : Monoclinic

• Any mineral that falls under the following specifications belongs to the monoclinic crystal system:Three axes, all of them are unequal in length. Two of them are at right angles to each other, while the third is lies at an angle other than 90°.

Page 39: UNIT-II MINERALOGY

AUGITE – PHYSICAL PROPERTIES

•Colour : dark green to black

•Streak : white to gray, augite can be slightly harder than a streak plate so brittle

fragments rather than a powder will sometimes be produced.

•Lustre : vitreous

•Diaphaneity : translucent to opaque

•Cleavage : prismatic

•Hardness : 5.5 – 6

•Specific Gravity : 3.2 - 3.6

•Distinguishing Characteristics : Two cleavage directions almost at right angles,

dark green to black colour

•Chemical Classification : silicate

Page 40: UNIT-II MINERALOGY

USES OF AUGITE

• Augite is a dark green to black mineral that is used for

ceramics.

• It contains large amounts of aluminum, iron, and

magnesium and can be found in meteroic stones.

• ceramic glazing, manufacturing aluminum, purifying water.

Page 41: UNIT-II MINERALOGY

41

AMPHIBOLE MINERALS

MONOCLINICORTHORHOMBIC

IV.AMPHIBOLES

Another type of mineral

Crystallization Important

Page 42: UNIT-II MINERALOGY

Amphibole Group – Resemble – Pyroxene GroupCHARACTERISTICS• HARDNESS: 5 – 6• SPECIFIC GRAVITY: 3 – 3.5• Dark in Colour

CHEMICAL COMPOSITION• Amphibole minerals – Metal silicates – Si : O – 4 : 11• Ca, Mg, Fe, Mn, Na, K, H – metallic ions• (OH) ions – F and Cl – • Chemical Formula – [Si4 O11]2 [OH]2• Various ions – Al, Mg, Fe, Ca, Na, K, H, F – replaced – giving rise to a variety of Amphibole

minerals

ATOMIC STRUCTURE• Difference – Amphiboles and Pyroxenes• Amphiboles – SiO4 tetrahedra – double chains• Reason – more complex than Pyroxenes – chemical composition

Page 43: UNIT-II MINERALOGY

PHYSICAL PROPERTIES• Crystallise in only 2 crystal systems• Dark in colour.• Hardness – 5 to 6• Specific Gravity – 2.8 to 3.6• Elongated• Slender• Often fibrous in nature

Orthorhombic AmphibolesANTHOPHYLLITE (Mg, Fe)3 [Si4O11]2 [OH]2

43

CRYSTAL SYSTEM Orthorhombic – thin, slender fibres

CLEAVAGE Perfect and Prismatic

COLOR Grey, brownish or greenish

HARDNESS 5.56 – 6

SP. GRAVITY 2.85 – 3.20

LUSTRE Vitreous

OPTICAL Optically (+)

OCCURRENCE Only in metamorphic rocks

Page 44: UNIT-II MINERALOGY

VARIETIES OF AMPHIBOLES

1. Hornblende

2. Tremolite

3. Actinolite

4. Asbestos

Hornblende is the most common variety

Page 45: UNIT-II MINERALOGY

AMPHIBOLE - 1.Hornblende

Page 46: UNIT-II MINERALOGY

Hornblende – Description

Chemical formula : Ca2(Mg,Fe)4Al(Si7Al)O22(OH,F)2

Any of a subgroup of amphibole minerals that are calcium-

iron-magnesium-rich and monoclinic in crystal structure.

Hornblende, occurs widely in metamorphic and igneous

rocks.

Common hornblende is dark green to black in colour and

usually found in middle-grade metamorphic rocks (formed

under medium conditions of temperature and pressure).

Such metamorphic rocks with abundant hornblende are

called amphibolite's.

Page 47: UNIT-II MINERALOGY

System : Monoclinic

• Block diagram showing the

relationship between the

crystallographic axes and the

indicatrix axes.

Page 48: UNIT-II MINERALOGY

OPTICAL PROPERTIES• Colour : distinctly coloured, shades of green, yellow-green, blue-

green and brown

• Composition : exhibits a wide range of compositions.

• Occurrence : common mineral found in a variety of geological

environments, i.e. in igneous, metamorphic and sedimentary rocks

• Alteration : may be altered to biotite, chlorite or other Fe-Mg

silicates

• Distinguishing Features : cleavage and grain shape, inclined

extinction, pleochroism

Page 49: UNIT-II MINERALOGY

PHYSICAL PROPERTIES• Colour : dark green to black.

• Streak : gray to greenish gray

• Lustre : vitreous

• Diaphaneity : translucent to nearly opaque

• Cleavage : good

• Hardness : 5.0 - 6.0

• Specific Gravity : 3.0 - 3.5

Page 50: UNIT-II MINERALOGY

USES

• The hornblende mineral is

used in a variety of common

things that we use every day.

• These things include: steel,

soap, oil, buildings, and

statues.

Page 51: UNIT-II MINERALOGY

Monoclinic Amphiboles – 2.Tremolite

CRYSTAL SYSTEM Monoclinic –long, bladed

CLEAVAGE Prismatic and Perfect

COLOUR White to light grey

HARDNESS 5.5 – 6.0

SP. GRAVITY 2.9 – 3.0

LUSTRE Vitreous

OPTICAL Optically (-)

OCCURRENCE Igneous and metamorphic rocks.. (mostly)

Ca2Mg5 [(Si4O11)]2 [OH]2

Page 52: UNIT-II MINERALOGY

CRYSTAL SYSTEM Monoclinic

CLEAVAGE Perfect and Prismatic

COLOUR Green due to ferrous ion

HARDNESS 5.5 – 6.0

SP. GRAVITY 3.1 – 3.3

VARIETY Asbestos – fibrous form – long and flexible fibres

Ca2 (Mg, Fe)5 [(Si4O11)]2 [OH]2

Monoclinic Amphiboles – 3. ACTINOLITE

Page 53: UNIT-II MINERALOGY

V. INTRODUCTION-MICA

• Mica is the name given to a group of

silicate minerals that

have silicon and oxygen as their two

major components.

• The Mica family of minerals includes

several variations based on chemical

composition and characteristics.

Page 54: UNIT-II MINERALOGY

Mica’s are besides feldspars, pyroxenes and amphiboles, very

common rock forming minerals comprising approximately 4

percent of the Earth.

They have great variation in their Chemical Composition.

Despite this, mica minerals are easily grouped together

because of their similar atomic structure.

(Mica’s yield water when heated in a closed test tube.)

Page 56: UNIT-II MINERALOGY

The 11 common variations are:1. Biotite2. Celadonite3. Fuchsite4. Glauconite5. Lepidolite6. Margarite7. Muscovite8. Phengite (or) Mariposite9. Phlogopite10. Sericite11. Stilpnomelane The many variations come from the diverse ways it formed. Mica formations are associated with volcanoes and hydrothermal vents.

Page 57: UNIT-II MINERALOGY

GENERAL FORMULA

Chemically, micas can be given the general formula

X2Y4–6 Z8 O20(OH,F)4

in which,X is K, Na, or Ca or less commonly Ba, Rb, or Cs;Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.;Z is chiefly Si or Al, but also may include Fe3+ or Ti.

Page 58: UNIT-II MINERALOGY

CHARACTERISTICS

• Mica has a brilliant shininess that glitters and sparkles. In fact the name mica is believed to have come from the Latin word ‘MICARE’ which means “to shine.”

• Mica is responsible for the flashes of light in composite rocks such as granite, gneiss, and slate.

• The crystal structure is monoclinic with a somewhat hexagonal crystal shape. These two characteristics are due to the structure of the atoms that make up the mica group.

Page 59: UNIT-II MINERALOGY

PROPERTIES

Name Content

Color White, Yellowish, Green, Gray

Streak Colorless

Luster Vitreous to Pearly

Transparency Transparent, Translucent and Opaque

Crystal System Monoclinic

Specific Gravity 2.8

Hardness(Mohs) 2.5-3

Cleavage Perfect

Page 60: UNIT-II MINERALOGY

Fracture Uneven

Uses Mainly as Insulators in Electronics

Location Mica is found in many rocks around the world. Notable deposits are found in India, South Dakota, Russia and Brazil. Larger deposits are found in Colorado(USA), Evje(Norway) and Minas Gerais(Brazil).

Page 61: UNIT-II MINERALOGY

BIOTITE

Page 62: UNIT-II MINERALOGY

DESCRIPTION OF BIOTITE

• General Formula: K2(Mg,Fe)3 AlSi3O10(OH,O,F2)2

• Biotite is a group of common rock-forming minerals

forming a series between phlogopite and annite. The name

is best used as a field name for dark micas for which the

exact composition has not been determined.

Page 63: UNIT-II MINERALOGY

DESCRIPTION OF BIOTITE – CONTD.

• Biotite survives a certain amount of weathering and is found in

soils, sediments and sedimentary rocks. Weathered Biotite

becomes relatively brassy of bronzy in colour and has been

mistaken for gold.

• Its lower density, cleavage, and other properties are soon

apparent to the careful observer. Finally Biotite can form as a

result of hydrothermal processes, especially wall-rock alteration

around ore veins.

Page 64: UNIT-II MINERALOGY

OPTICAL PROPERTIES

• Colour: Typically brown, brownish green or reddish brown.

• Occurrence: Common in a wide range of igneous and metamorphic rocks

and may be an important detrital mineral in sediments.

• Cleavage: Perfect cleavage on {001}.

• Twinning: Rarely visible.

• Optic Orientation: Extinction is parallel or nearly parallel, with a maximum

extinction angle of a few degrees. Cleavage traces are length slow.

• Alteration: Alters to chlorite, clay minerals, and/or sericite, iron-titanium

oxides, epidote, calcite, and sulphides

• Distinguishing Features : colour, "birds-eye" extinction, nearly parallel

extinction

Page 65: UNIT-II MINERALOGY

BIOTITE - PHYSICAL PROPERTIES

• Colour: black, dark green, dark brown

• Streak: white to gray.

• Lustre: vitreous.

• Diaphaneity: transparent to translucent.

• Cleavage: basal, perfect

• Hardness: 2.5 – 3

• Specific Gravity: 2.7 - 3.3

• Chemical Classification: silicate

Page 66: UNIT-II MINERALOGY

BIOTITE - USES

•Biotite has very limited commercial use.

•Biotite particles are sometimes used as a surface treatment in

decorative concrete, plaster and other construction materials.

•It is also used in the potassium-argon method of dating igneous

rocks.

Page 67: UNIT-II MINERALOGY

MUSCOVITE

Page 68: UNIT-II MINERALOGY

OCCURRENCE

• A common rock forming mineral, muscovite is found in

igneous, metamorphic and detrital sedimentary rocks.

• It is not usually valuable as a mineral specimen but can be

found associated with other valued minerals such as

tourmaline, topaz, beryl, almandine and others.

Page 69: UNIT-II MINERALOGY

MINERAL DESCRIPTION

• Chemical formula : KAl2(AlSi3O10)(F,OH)2

• MUSCOVITE was once commonly used for windows.

• The Russian mica mines that produced it gave muscovite its name (it

was once widely known as "Muscovy glass").

• Muscovite is a high-aluminium member of the mica family of minerals,

all known for the property of perfect basal cleavage; cleavage layers

can be easily peeled off into very thin sheets which are quite durable

and are not easily destroyed by erosion.

• Muscovite sheets have high heat and electrical insulating properties

and are used to make electrical components.

Page 70: UNIT-II MINERALOGY

OPTICAL PROPERTIES• Colour : colourless

• Composition : highly variable

• Form : found as micaceous flakes or tablets with irregular outlines

• Twinning : rare

• Optic Orientation : parallel extinction, cleavage traces are length slow

• Alteration : not generally altered

• Distinguishing Features : colourless, parallel extinction, "birds-eye" extinction

• Bird's eye maple, or bird's eye extinction, is a specific type

of extinction exhibited by minerals of the mica group under cross polarized light

(sometimes called the optical analyser). It gives the mineral a pebbly

appearance as it passes into extinction.

Page 71: UNIT-II MINERALOGY

SYSTEM: MONOCLINIC

• Block diagram showing the

relationship between the

crystallographic axes and

the indicatrix axes.

Page 72: UNIT-II MINERALOGY

MUSCOVITE - PHYSICAL PROPERTIES

• Colour : colourless, yellow, brown,

green, red

• Streak : white

• Lustre : vitreous

• Diaphaneity : transparent to translucent

• Cleavage : perfect

• Hardness : 2.5 – 3

• Specific Gravity : 2.8 - 2.9

• Chemical Classification : silicate

Page 73: UNIT-II MINERALOGY

MUSCOVITE – USES

• Muscovite has a high resistance to

heat and, split into thin

transparent sheets, it has been

used as windows on high-

temperature furnaces and ovens.

• It is an insulator and was used in

the past to make circuit boards.

• Historically, it was used as an early

window glass.

Page 74: UNIT-II MINERALOGY

CALCITE

Page 75: UNIT-II MINERALOGY

CALCITE - DESCRIPTION

• Calcite is a rock-forming mineral with a chemical formula of

CaCO3.

• It is extremely common and found throughout the world

in sedimentary, metamorphic and igneous rocks.

• Calcite is the principal constituent of limestone and marble.

• These rocks are extremely common and make up a

significant portion of Earth's crust.

• They serve as one of the largest carbon repositories on our

planet.

Page 76: UNIT-II MINERALOGY

CALCITE - DESCRIPTION – CONTD.

• The properties of calcite make it one of the most widely used

minerals.

• It is used as a construction material, abrasive, agricultural soil

treatment, construction aggregate, pigment, pharmaceutical and

more.

• It has more uses than almost any other mineral.

Page 77: UNIT-II MINERALOGY

CRYSTAL SYSTEM

• The true rhombohedral unit cell, which is the acute rhombohedra, and the cleavage rhombohedron setup.

• The true unit cell includes 2 CaCO3 with calcium ions at the corners of the rhombohedron and CO3 groups.

• Each of which consists of a carbon ion at the centre of a planar group of oxygen atoms whose centres define an equilateral triangle.

Page 78: UNIT-II MINERALOGY

CALCITE – PHYSICAL PROPERTY

• Mineral class : Carbonates - Calcite group.

• Cleavage : Perfect rhomboedric in three planes, subconchoidal

fracture.

• Hardness : 3

• Density : 2.7

• Colour : usually colourless, but nuances in blue, yellow, green,

red, violet, even black and opaque.

• Streak : White to greyish.

• Lustre : Vitreous to pearly or dull.

Page 79: UNIT-II MINERALOGY

USES OF CALCITE IN CONSTRUCTION

• The construction industry is the primary consumer of calcite

in the form of limestone and marble.

• These rocks have been used as dimension stones and in

mortar for thousands of years.

• Limestone blocks were the primary construction material

used in many of the pyramids of Egypt and Latin America.

• Today, rough and polished limestone and marble are still an

important material used in prestige architecture.

Page 80: UNIT-II MINERALOGY

USES OF CALCITE IN CONSTRUCTION – CONTD.

• Modern construction uses calcite in the form of limestone and

marble to produce cement and concrete.

• These materials are easily mixed, transported and placed in the

form of a slurry that will harden into a durable construction

material.

• Concrete is used to make buildings, highways, bridges, walls .

Page 81: UNIT-II MINERALOGY

OTHER USES OF CALCITE

• In a powdered form, calcite often has an extremely white colour.

• Powdered calcite is often used as a white pigment or "whiting".

• Some of the earliest paints were made with calcite. It is a primary

ingredient in whitewash and it is used as an inert colouring

ingredient of paint.

• It is softer than the stone, porcelain and plastic surfaces found in

kitchens and bathrooms but more durable than dried food and

other debris that people want to remove .• This is a non-flammable dust that is sprayed onto the walls and

roofs of underground coal mines to reduce the amount of coal dust.

Page 82: UNIT-II MINERALOGY

GYPSUM (CaSO4.2H2O)

• Gypsum- a soft sulphate mineral composed of calcium

sulphate di hydrate.

• Gypsum was known in Old English as spærstān, "spear

stone", referring to its crystalline projections.

• Dehydrated gypsum is popularly known as “plaster of

Paris”.

• Gypsum crystals contain anion water and hydrogen

bonding.

Page 83: UNIT-II MINERALOGY

PROPERTIES

• Category• Colour

• Cleavage

• Mohs scale• Lustre • Specific

gravity• Solubility

-Sulphate minerals-White, colorless. May be pink, brown, red due to impurities.-Perfect on 010 distinct on 100 -1.5-2-Vitreous to silky, pearly or waxy.-2.31 to 2.33-Hot, dilute Hcl

Page 84: UNIT-II MINERALOGY

GYPSUM CRYSTALS

Page 85: UNIT-II MINERALOGY

APPLICATIONS

• Used as cement blocks in building.• An ancient mortar used in building construction.• Binder in fast-dry tennis courts.• Fertilizer and soil conditioner.

Page 86: UNIT-II MINERALOGY

CLAY

Page 87: UNIT-II MINERALOGY

• Clay- a fine grained soil.

• Distinguished from other soil by size.

• Formed by gradual weathering of rocks.

• Absorb or lose water depending on humidity changes.

• Due to absorption of water, specific gravity of clay is

variable.

• Divided into kaolinite, illite, vermiculite, smectite and

chlorite.

Page 88: UNIT-II MINERALOGY

PRODUCTION

Page 89: UNIT-II MINERALOGY

USES

• Used in pottery, decorative and construction products.

• Macaws use clay licks for survival.

• Can soothe an upset stomach.

• Primary ingredient in building techniques.

• Kaolin clay – used as anti-diarrheal medicines.

• Removal of heavy metals from waste water.

Page 90: UNIT-II MINERALOGY
Page 91: UNIT-II MINERALOGY

PROPERTIES QUARTZ FELSPAR GROUP

MUSCOVITE

BIOTITE MICA GYPSUM

CRYSTAL SYSTEM

Hexagonal

Monoclinic and Triclinic

Monoclinic

Monoclinic Monoclinic Category of sulphate

COLOUR Colourless when pure; red, green, blue

Grey, green, blue, pink and white

White to Colourless

Greenish to brown or black; even yellow

White, yellowish, green, grey

White, colourless

HARDNESS 7 6 – 6.5 2 – 2.5 2.5 - 3 2.5 - 3 1.5 - 2

SPECIFIC GRAVITY

2.65 – 2.66

2.54 – 2.57 2.76 - 3 2.7 – 3.1 2.8 2.31 – 2.33

CLEAVAGE Generally absent

Perfect Highly perfect basal cleavage

Highly perfect basal cleavage

Perfect Perfect

LUSTRE Vitreous Vitreous Vitreous Vitreous Vitreous Vitreous

Page 92: UNIT-II MINERALOGY

PROPERTIES AMPHIBOLE MINERALS

CALCITE

CRYSTAL SYSTEM

Monoclinic Crystalline, granular, rhombohedra

COLOUR White to light grey White or colourless; also grey, yellow & green

HARDNESS 5.5 – 6 3

SPECIFIC GRAVITY

2.9 - 3 2.71

CLEAVAGE Perfect Perfect with 74’

LUSTRE Vitreous Vitreous


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