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MINEROLOGY
Acknowledging
Monika, Syed, Priyanka, Nitin, Sai Pradeep and
Srivatsan
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
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 violet
2. Smoky- dark to light brown, even black
3. Milky- pure white and opaque
4. Rose red – colour is attributed to presence of titanium.
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UNIT I General Geology
Cryptocrystalline types :
1.
2.
3.
4.
5.
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 :
Chalcedony – luster ,waxy, commonly translucent, generally massive.
Agate – often banded , opaque and massive.
Onyx – a regularly banded agate having alternating and evenly paced layers of different colours.
Flint – a dull opaque variety of chalcedony breaking with characteristic conchoidal fracture.
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.
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UNIT I General Geology
PIEZOELECTRICITY
Quartz 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
AMETHYSTINE QUARTZ
CITRINES
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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 series
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ATOMIC 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.
Crystallization
The 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.
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UNIT I General Geology
Crystallographically ,felspar fall in two crystal systems .
Monoclinic Felspars
1. Orthoclase (KAlSi3O8 )
2. Sanidine (KAlSi3O8 )
Triclinic Felspars
1. 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.
1.
2.
3.
4.
Among the felspar group, the following mineral species are quite common as rock forming
minerals and hence are described in detail.
Orthoclase
Microcline
Albite
Anorthite
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UNIT I General Geology
Orthoclase
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
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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UNIT I General Geology
albite
Crystal 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.
UNIT I General Geology
anorthite
Crystal 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.
UNIT I General Geology
Amphibole Group – Resemble – Pyroxene Group
CHARACTERISTICS
• 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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AMPHIBOLE MINERALS
ORTHORHOMBIC
MONOCLINIC
Crystals – long, slender, prismatic, sometimes fibrous
Prism angle – 124’
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PHYSICAL PROPERTIES
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•
•
•
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•
•
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
ANTHOPHYLLITE (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
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TREMOLITE
Ca2Mg5 [(Si4O11)]2 [OH]2
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)
ACTINOLITE
Ca2 (Mg, Fe)5 [(Si4O11)]2 [OH]2
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
UNIT I General Geology
AUGITE
UNIT I General Geology
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.
UNIT I General Geology
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°.
UNIT I General Geology
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
UNIT I General Geology
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.
UNIT I General Geology
Hornblende
UNIT I General Geology
Hornblende – Description
• Chemical formula : Ca2(Mg,Fe)4Al(Si7Al)O22(OH,F)2
• Any of a subgroup of amphibole minerals that are calciumiron-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.
UNIT I General Geology
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
UNIT I General Geology
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
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
Biotite - Physical Properties
•
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•
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•
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•
•
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
UNIT I General Geology
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.
UNIT I General Geology
Muscovite
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
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
UNIT I General Geology
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.
UNIT I General Geology
Calcite
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
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
UNIT I General Geology
GARNET
UNIT I General Geology
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.
UNIT I General Geology
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.
UNIT I General Geology
Crystal System: Isomeric
UNIT I General Geology
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
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•
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•
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•
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.
Ca2Na (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
Na2 (Mg, Fe)3Al2 [Si4O11]2 [OH, F]2
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 (-)
ARFVEDSONITE
Na3 (Mg, Fe)4 (Fe, Al) [Si4O11]2 [OH, F]2
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!
UNIT I General Geology
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.)
UNIT I General Geology
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.
UNIT I General Geology
General Formula
Chemically, 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.
UNIT I General Geology
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.
UNIT I General Geology
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
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).
UNIT I General Geology
• 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
Name
• 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.
UNIT I General Geology
UNIT I General Geology
UNIT I General Geology
•
•
•
•
•
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
Physical properties
•
•
•
•
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
UNIT I General Geology
Uses
• 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.
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)
3AlSi
3O
10(F,OH)2
• Biotite was named by J.F.L. Hausmann in 1847.
UNIT I General Geology
Occurence
• 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.
UNIT I General Geology
Thin tabular biotite
UNIT I General Geology
Properties
•
•
•
•
•
•
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.
UNIT I General Geology
Uses
• 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.
UNIT I General Geology
UNIT I General Geology
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
UNIT I General Geology
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.
UNIT I General Geology
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
UNIT I General Geology
GYPSUM CRYSTALS
UNIT I General Geology
APPLICATIONS
• Used as cement blocks in building.
• An ancient mortar used in building
construction.
• Binder in fast-dry tennis courts.
• Fertilizer and soil conditioner.
UNIT I General Geology
CLAY
UNIT I General Geology
• 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
UNIT I General Geology
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.
UNIT I General Geology
PROPERTI QUARTZ
ES
FELSPAR
GROUP
MUSCOVI BIOTITE
TE
MICA
GYPSUM
CRYSTAL
SYSTEM
Hexagona Monoclini Monoclini Monoclini Monoclini Category
l
c and
c
c
c
of
Triclinic
sulphate
COLOUR
Colourles
s when
pure; red,
green,
blue
Grey,
White to
green,
Colourles
blue, pink s
and white
Greenish
to brown
or black;
even
yellow
White,
White,
yellowish, colourless
green,
grey
HARDNES 7
S
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
CLEAVAG
E
Generally Perfect
absent
Highly
perfect
basal
cleavage
Highly
perfect
basal
cleavage
Perfect
Perfect
LUSTRE
Vitreous
Vitreous
Vitreous
Vitreous
Vitreous
Vitreous
UNIT I General Geology
PROPERTIES
AMPHIBOLE
MINERALS
CRYSTAL SYSTEM Monoclinic
CALCITE
COLOUR
White to light
grey
HARDNESS
5.5 – 6
Crystalline,
granular,
rhombohedra
White or
colourless; also
grey, yellow &
green
3
SPECIFIC
GRAVITY
CLEAVAGE
2.9 - 3
2.71
Perfect
Perfect with 74’
LUSTRE
Vitreous
Vitreous