MINEROLOGY Acknowledging

Monika, Syed, Priyanka, Nitin, Sai Pradeep and Srivatsan

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UNIT I General Geology

CONTENTS

UNIT II MINEROLOGY

Physical properties of minerals – Quartz group, Feldspar group, Pyroxene – hypersthene and augite, Amphibole – hornblende, Mica – muscovite and biotite, Calcite, Gypsum and clay minerals

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UNIT I General Geology

quartz

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Crystal system

Hexagonal, (rhombohedral). Crystals common ; some crystals weighing many tones have been reported. Twinned ,right-handed and left-handed crystals are common.

Cleavage Generally absent

Fracture Conchoidal

Colour Colourless when pure, quartz also occur in coloured varieties :red, green , blue and mixture.

Hardness 7

Sp. Gravity 2.65-2.66

Streak White in coloured varieties

Varieties It is a very common rock forming mineral and occurs in numerous varieties . A few common varieties are mentioned below.

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Polymorphous transformation Quartz, 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 : Α quartz, β quartz. Identification of the exact type of quartz (into Αand β) requires thorough

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 in distinct crystals ,quartz may be distinguished into right handed and left handed types. This is done 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.

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UNIT I General Geology• 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.

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UNIT I General Geology

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.Sivapriya Vijayasimhan

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UNIT I General Geology

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

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UNIT I General Geology

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AMETHYSTINE QUARTZ

CITRINES

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UNIT I General Geology

Felspar group • The feldspars are the most prominent group of minerals making more

than fifty percent , by weight ,crust of the earth up to a depth of 30 km.• These occur chiefly in the igneous rocks(more than 60 percent) but also

form a good portion of their metamorphic derivatives.• Felspars are also found in some sedimentary rocks like arkose and

greywacks.• The group comprises about a dozen or so minerals of which 3-4 may be

easily described as the most common minerals in rocks.

CHEMICAL COMPOSITION• In chemical constitution , felspars are chiefly aluminosilicates 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 seriesSivapriya Vijayasimhan

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UNIT I General GeologyATOMIC STRUCRURE 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 tetrahedra. The SiO4 tetrahedra is accompanied by AlO4 tetrahedra so that the felspar are complex three dimensional framework of the

above two types of tetrahedra. The resulting network is negatively charged and these negative charges are satisfied by the presence of positively charged

K,Na,Ca and Ba.

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

CrystallizationThe felspar 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 felspar : These are also called the plagioclase felspars 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.Sivapriya Vijayasimhan

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UNIT I General GeologyCrystallographically ,felspar fall in two crystal systems . Monoclinic Felspars1. Orthoclase (KAlSi3O8 )

2. Sanidine (KAlSi3O8 )

Triclinic Felspars1. Microcline (KAlSi3O8 )

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

• They are generally light in colour, have lower specific gravity ,have a double cleavage and a hardness varying between 6-6.5.

Among the felspar group, the following mineral species are quite common as rock forming minerals and hence are described in detail.

1. Orthoclase 2. Microcline3. Albite4. Anorthite Sivapriya Vijayasimhan

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UNIT I General Geology

Orthoclase

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Crystal 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

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microcline

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Crystal 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.

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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.

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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.

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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

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UNIT I General Geology

Crystallization

Crystals – long, slender, prismatic, sometimes fibrousPrism angle – 124’

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AMPHIBOLE MINERALS

MONOCLINICORTHORHOMBIC

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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

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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

Monoclinic AmphibolesTREMOLITE

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

ACTINOLITE

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

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AUGITE

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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.

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Occurrence

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

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°.

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Augite – Physical Properties• Color : 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.• Luster : 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 color• Chemical Classification : silicate

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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.

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Hornblende

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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 amphibolites.

System : Monoclinic

• Block diagram showing the relationship between the crystallographic axes and the indicatrix axes.

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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

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Physical Properties

• Color : dark green to black.• Streak : gray to greenish gray• Luster : vitreous• Diaphaneity : translucent to nearly opaque• Cleavage : good• Hardness : 5.0 - 6.0• Specific Gravity : 3.0 - 3.5

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.

BIOTITE

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Description of Biotite

• General Formula: K2(Mg,Fe)3AlSi3O10(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.

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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 color 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. The localities listed below highlight typical or remarkable biotite occurrences in the state.

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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

System: Monoclinc

• Block diagram showing the relationship between the crystallographic axes and the indicatrix axes.

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Biotite - Physical Properties

• Color: black, dark green, dark brown• Streak: white to gray.• Luster: vitreous.• Diaphaneity: transparent to translucent.• Cleavage: basal, perfect• Hardness: 2.5 – 3• Specific Gravity: 2.7 - 3.3• Chemical Classification: silicate

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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.

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Muscovite

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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 is a high-aluminum 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.

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Occurrence

• A common rock forming mineral, muscovite is found in igneous, metamorphic and detrital sedimentary rocks.

• It is not usually valuable as a mineral speciemen but can be found associated with other valued minerals such as tourmaline, topaz, beryl, almandine and others.

UNIT I General Geology

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 analyzer). It gives themineral a pebbly appearance as it passes into extinction.

System: Monoclinic

• Block diagram showing the relationship between the crystallographic axes and the indicatrix axes.

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Muscovite - Physical Properties

• Color : colorless, yellow, brown, green, red

• Streak : white• Luster : vitreous• Diaphaneity : transparent to

translucent• Cleavage : perfect• Hardness : 2.5 – 3• Specific Gravity : 2.8 - 2.9• Chemical Classification : silicate

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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.

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Calcite

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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.

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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.

Crystal System• The true rhombohedral

unit cell, which is the acute rhombohedron, and the cleavage rhombohedron setup.

• The true unit cell includes 2 CaCO3 with calcium ions at the corners of the rhombohedrons 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.

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Calcite – Physical Property

• Mineral class : Carbonates - Calcite group.• Cleavage : Perfect rhomboedric in three planes,

subconchoidal fracture.• Hardness : 3• Density : 2.7• Color : usually colorless, but nuances in blue, yellow, green,

red, violet, even black and opaque.• Streak : White to grayish.• Luster : Vitreous to pearly or dull.

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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.

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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

and many other structures.

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Other Uses of Calcite• In a powdered form, calcite often has an extremely white color. • 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 coloring 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 nonflammable dust that is sprayed onto the walls and roofs of underground coal mines to reduce the amount of coal dust in the air

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GARNET

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GARNET - Description

• General Formula: X3Y2(SiO4)3 • Where X = Ca, Mg, Fe2+, Mn• Y = Al, Fe3+, Cr• Garnet is a more complex orthosilicate in

which the SiO4 tetrahedra are still independent.• Although valued as a gem stone, garnet is

generally of low monetary value because of its relatively common occurrence.

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Occurrence

• Garnet is commonly found in highly metamorphosed rocks and in some igneous rocks.

• They form under the same high temperatures and / or pressures that form those types of rocks.

• Garnets can be used by geologists to gauge the temperature and pressure under which a particular garnet-bearing rock

formed.

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Crystal System: Isomeric

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Crystal structure• Garnet is made up of three calcium,

two aluminum, three silicon and 12 oxygen atoms.

• The oxygen atoms are bonded to two calcium, one aluminum and one silicon atom.

• The silicon atoms are bonded to four oxygen atoms (called tetrahedra).

• The aluminum atoms are bonded to six oxygen atoms (called octahedra) and the calcium atoms are bonded to eight oxygen atoms (called a distorted cube).

UNIT I General Geology

Physical Properties

• Hardness - 6.5-7.5• Specific gravity - 3.6-4.3• Transparency - Transparent to opaque• Colour - Variable - most commonly red, reddish brown• Streak - White• Lustre - Vitreous to resinous• Cleavage/fracture - Non-existent / conchoidal• Crystal habit/mode of occurrence - Prismatic (12-

sided rhombic, 24-sided trapezoidal) / granular,massive

Garnet - Uses• Garnet has no free silica and hence

does not cause dust and silicosis in its industrial applications unlike silica sand or quartzite.

• Garnet is non-toxic, inert and hence environment (eco) friendly.

• Garnet is well suited for abrasive blasting / surface cleaning in fields like shipyards, petrochemical industry, building industry, non-ferrous surfaces etc.

HORNBLENDECa2Na (Mg, Fe) (Al, Fe) [(SiAl)4O11]2 [OH]2

CRYSTAL SYSTEM Monoclinic – long, slender & prismatic

CLEAVAGE Perfect and Prismatic

COLOUR Dark green, dark brown, black

HARDNESS 5.5 – 6

SP. GRAVITY 3.0 – 3.47

LUSTRE Vitreous

STREAK White with greenish tint.

COMPOSITION Highly variable & Complex; broadly an aluminous amphibole

OPTICAL Optically (-)

OCCURRENCE Hornblende is a common rock forming mineral in Igneous and metamorphic rocks. Amphibolite, a metamorphic group of rock may be made up chiefly of hornblende.

VARIETIES Differentiated on the basis of Chemical Composition

GLAUCOPHANE

This Monoclinic Amphibole is confined in its occurrence to Crystalline metamorphic rocks called SCHISTS. It commonly occurs in grains or fibrous aggregates.

COLOUR – Various shades of Blue

HARDNESS – 6 – 6.5 SP. GRAVITY – 3.1 – 3.2

In Composition, Glaucophane differs from other amphiboles in that a part of hydroxyl group is replaced by fluorine. It is Optically (-)

Na2 (Mg, Fe)3Al2 [Si4O11]2 [OH, F]2

ARFVEDSONITE

It is also a monoclinic amphibole, characterised with a prismatic cleavage. It is rich in iron and magnesium and hence is BLACK in colour as compared with glaucophane. Streak-deep blue.

HARDNESS – 6 SP. GRAVITY – 3.4

Optically (-)

The mineral occurs chiefly in Igneous rocks such as Syenites and Pegmatites. In the latter rocks, it may occur in the form of crystals of appreciable size: 10 to 20 cm in length!

Na3 (Mg, Fe)4 (Fe, Al) [Si4O11]2 [OH, F]2

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Introduction

• 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.

UNIT I General Geology

• Mica’s are besides felspars, 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.)

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Different types

The 11 common variations are:• Biotite• Celadonite• Fuchsite• Glauconite• Lepidolite• Margarite• Muscovite• Phengite (or) Mariposite• Phlogopite• Sericite• Stilpnomelane

The many variations come from the diverse ways it formed. Mica formations are associated with volcanoes and hydrothermal vents.

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General FormulaChemically, micas can be given the general formula

X2Y4–6Z8O20(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.

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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.

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PropertiesName 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

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).

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• Muscovite -also known as mica,isinglass, or potash mica.

• Phyllosilicate mineral of aluminium and potassium.

• General formula is KAL2(ALSi3O10 )(F,OH)2.• Muscovite is common in many different rock

types as a primary mineral.• Fuchsite and mariposite are the common

types of muscovite.

UNIT I General Geology

• The earliest names attributable to muscovite include: Muscovy Glass, Cat Silver, and Lapis Specularis.

• The stand-alone name 'Muscovite' was used by Johann Gottfried Schmeisser in 1974 in his system of minerology.

• Muscovite was earlier called mica,isinglass and glimmer.

Name

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• Muscovite has a Mohs hardness of 2–2.25• It has a specific gravity of 2.76–3• It is anisotropic and has high birefringence.• Its crystal system is monoclinic.• It has a highly-perfect basal cleavage yielding

remarkably-thin laminæ (sheets) which are often highly elastic.

• Sheets of muscovite 5×3 m have been found in Nellore, India.

UNIT I General Geology

• Lustre- Vitreous,silky or pearly.• It can be transparent or translucent.• Colour: White to colourless.• It can be changed to other colours on addition

of impurities.• It is highly elastic.• Density ranges from 2.77-2.88 gm/cm3

Physical properties

UNIT I General Geology

• Muscovite is found in immense sheets that are commercially valuable.

• It is in demand for the manufacture of fireproofing material.

• They are also used as insulating materials.• In some cases, they can be used as lubricants.

Uses

BIOTITE

UNIT I General Geology

• Biotite is a common phyllosilicate mineral within the mica group.

• Generally, it refers to the dark mica series, primarily a solid-solution.

• It is also known as ‘Black mica’ or ‘Iron mica’.• The chemical formula is K(Mg,Fe)

3AlSi3O10(F,OH)2

• Biotite was named by J.F.L. Hausmann in 1847.

UNIT I General Geology

• Biotite is found in a wide variety of igneous and metamorphic rocks.

• Biotite occurs in the lava of Mount Vesuvius.• Biotite is occasionally found in large cleavable crystals,

in New England, Virginia and North Carolina.• It is also an essential constituent of many

metamorphic schists.• The largest documented single crystals of biotite were

approximately 7 m2 (75 sq ft) sheets found in Iveland, Norway.

Occurence

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Thin tabular biotite

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• Biotite has a monoclinic crystal system.• Its hardness on the Mohs scale is from 2.5-3.• The specific gravity ranges from 2.7-3.1.• It has a vitreous to pearly lustre.• The density of biotite ranges from 2.8-3.3.• It appears greenish to brown or black, and even

yellow when weathered.• It can be transparent to opaque.• Biotite has a highly perfect basal cleavage.

Properties

UNIT I General Geology

• Biotite has a small number of commercial uses.• Biotite is used to determine the ages of rocks by

potassium argon-dating or argon-argon dating.• It is also used as a filler and as an extender in paints.• Biotite can be used as an additive to drilling muds.• And finally it can also be used as a mold release

agent in rubber products.

Uses

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CALCITE

• Has its name from Greek word “chalix” meaning lime.

• Comprises 4% of weight of earths crust. • Most stable polymorph of calcium

carbonate(CaCO3).

Calcite (CaCO3)• Color

• Crystal habit • Cleavage

• Mohs scale hardness

• Lustre • Specific

gravity

• White or colorless, also gray, yellow and green.

• Crystalline, granular, stalactitic, rhombohedral.

• Perfection on three directions with an angle of 74 degrees.

• 3 (defining mineral)

• Vitreous. Sometimes earthy.• 2.71

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USES OF CALCITE• Mainly used for cement production.• Also used for manufacture of steel and glass.• Limestone and marble are used for interior

decoration and sculpture.

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GYPSUM (CaSO4.2H2O)

• Gypsum- a soft sulphate mineral composed of calcium sulphate dihydrate.

• 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.

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

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GYPSUM CRYSTALS

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APPLICATIONS• Used as cement blocks in building.• An ancient mortar used in building

construction.• Binder in fast-dry tennis courts.• Fertilizer and soil conditioner.

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CLAY

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• 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.

PRODUCTION

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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.

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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

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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 3SPECIFIC GRAVITY

2.9 - 3 2.71

CLEAVAGE Perfect Perfect with 74’

LUSTRE Vitreous Vitreous