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EARTH’S COMPONENTS 

Prepared by: Dr. J.Seetharamaiah

The earth surface is covered by 28%land, 78% water this is unlike any other known planethydrosphere. It includes: oceans, lakes, seas, rivers, ice and aquifers. Most of the land is within

1km above sea level and most of the seafloor is between 3-4 km deep. The main categories of 

materials that make up the earth are:

Minerals: Solid, inorganic substances with atoms arranged in an orderly pattern. Example:

quartz, calcite, pyrite, diamond.

Glasses: Solid, inorganic substances with atoms randomly arranged, forms when a liquid freezestoo fast to organize into a pattern. Example: window glass is quartz is melted then frozen

quickly.

Rocks: aggregates of minerals and/or glasses

Metals: solid mode entirely of metal atoms, rarely but occasionally occur in nature. Example:

native gold, copper, iron.

Melts: form when rock, minerals and /or glasses become hot and transform to liquid. Magma is

a melt beneath the surface; lava is a melt on the earth’s surface. 

Volatiles: Materials that are gases at low temperature found at earth’s surface, such as water,

CO2, methane.

Minerals: Definition: a homogeneous, naturally occurring, solid, inorganic substance with a

definable chemical composition and an orderly internal arrangement of atoms.

The minerals are formed by three ways:

1.  Solidification of a melt: Eg: Olivine, Mica, Quartz

2.  Precipitation from solution. Eg. Gypsum, Halite

3.  Solid-state diffusion. Eg. Kyanite, sillimanite

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The minerals are destroyed by melting, dissolving and chemical reaction (oxidation, solid-phase

reactions).

GENERAL CLASSIFICATION OF MINERALS

Rocks consist of various minerals which are called Rock Forming Minerals. Some of them are useful for 

industry (eg. Feldspar  Ceramics, and Glass industry, or Diatomite, a sedimentary rock  Sugar 

industry) and are called Industrial Minerals and Rocks. Some minerals have high concentrations of 

metallic elements (eg.Chalcopyrite-Cu, Galena  – PbS), from which metals and valuable elements are

extracted, which are called Ore Minerals. Some minerals are used for decorative purposes (eg. iamond;

Corundum, Ruby, Sapphire; and Beryl, Aquamarine, Emerald) which are called Gemstones. When

HT/HP rocks consisting of Primary minerals are brought to surface by tectonic forces rock forming

minerals are decomposed and altered to Secondary minerals, which may be grouped as Clay minerals,Serpentine minerals etc.

Classification of minerals based on Chemical Composition

There are approximately4,000 known minerals , however, only about 100 are relatively common. Based

on chemical composition seven principle classes of minerals are devided:

1.  Silicates, 2. Oxides, 3. Sulfides, 4. Sulfates, 5. Halides, 6. Carbonates and 7. Native elemants.

Silicates

We might expect combinations of O and Si to be common and all silicates based on Si-O tetrahedron (4

faces). SiO4 has net charge of -4 (a complex ion), electrical neutrality accomplished 2 ways: 1. addition of 

 positive ions (metals: Fe, Mg, K, Na Al, Ca) and 2. sharing of O by 2 or more Si by creating networks of 

SiO4 tetrahedra. 

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All rock forming silicate minerals are grouped into five divisions:

1. Nesosilicates: single tetrahedra: O on 4 corners, Si at center: example: olivine (Mg, Fe)2 Si O 4 

2.  Sorosilicates: double tetrahedra: relatively rare Ex: epidote: a green gemstone.

3.  Cyclosilicates: ring silicates-Ex: Beryl (Be3Al2(SiO3)6 

4.  Inosilicates: a) Single chains: Ex: pyroxenes

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 b) Double chains: Ex: amphiboles

c) sheet silicates : Ex: micas: muscovite (white), biotite lack)

5.  Tectosilicates, or "framework silicates," have a three-dimensional framework of silicate tetrahedra

with SiO2 or 1:2 ratio. This group comprises nearly 75% of the crust of the Earth. 

InTectosilicates two major groups are present: a) Quartz group: Ex: Quartz-SiO2 second most

abundant mineral in crust and b) Feldspar group: Most abundant mineral in crust. The feldspar group

consisting of Alkali-feldspars or Potassium-feldspars (Microcline - KAlSi3O8 and Orthoclase -

KAlSi3O8 ) and Plagioclase feldspar (Albite - NaAlSi3O8, Oligoclase - (Na,Ca)(Si,Al)4O8 (Na:Ca 4:1),

Andesine - (Na,Ca)(Si,Al)4O8 (Na:Ca 3:2), Labradorite - (Na,Ca)(Si,Al)4O8 (Na:Ca 2:3), Bytownite -

(Na,Ca)(Si,Al)4O8 (Na:Ca 1:4), Anorthite - CaAl2Si2O8.

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Sulfides

Sulfides are minerals composed of metal contains combined with sulfur in the form of sulfide ions (S2-,

S22-

). Example: Galena PbS; Pyrite FeS2; Sphalerite ZnS

Sulfides form in reduced (low oxygen) environments.

Sulfates Sulfates are minerals composed of metal cations combined with sulfur in the form of sulfate ions: SO 4 

2-

Example- CaSO4 2 H2O Gypsum.

Carbonates

Carbonates are minerals composed of metal cations combined with carbon in the form of carbonate ions:

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Oxides

Oxide minerals composed of metal cations combined with oxygen in the form of O2-

HalidesHalides are minerals composed of metal cations combined with anions of the halogen elements (chlorine,

iodine, fluorine, bromine)

Native Elements:

Minerals composed of atoms of a single element are referred to as native elements. Example :

The important silicate rock-forming minerals can also be classified based on iron and magnesium

content.

Ferromagnesium minerals Non-ferromagnesium minerals

Contain Fe and /or mg contain no Fe or Mg

Dark (brown, black, green light (gray, pink, white

Density about 3.0 g/cm3 density about 2.7 g/cm3

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minerals: olivine quartz

augite orthoclase

hornblende plagioclase

 biotite muscovite

Identification of minerals in the filed

Every mineral species possesses a Unique set of properties that results from its unique

combination of chemical composition, chemical bonding mechanism and crystal structure.

In the field, correct mineral identification generally depends on the accurate identification of 

macroscopic properties (physical properties)

•  External Crystal Form and habit: shape of crystal growth habit

•  Cleavage: way in which the mineral breaks or cleaves

•  Fracture

•  Hardness: Moh’s hardness scale

•  Specific Gravity: ratio of density of mineral vs water 

•  Color 

•  Streak: color of the pulverized mineral

•  Luster: : way in which mineral surface scatters light

•  Tenacity

• 

Transparency

The more important physical properties of minerals are: a) Crystal form, b) cleavage, c)

hardness, d) density, e) streak and luster. Other physical properties such as color, tenacity,

reaction with hydrochloric acid and magnetism are important properties of some minerals.

CRYSTAL FORM OR HABIT - The external morphology of crystals generally reflect the

internal arrangement of their constituent atoms and can be used to identify many mineral species.

Mineral with a definite internal atomic structure without development of well-defined faces is

said to be crystalline. In this case the mineral is said to high crystallised. Garnet, staurolite etc.

The external morphology of crystals generally reflect the internal arrangement of their 

constituent atoms. Example: Halite

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A mineral is said to be cryptocrystalline when degree of crystallization is noticeable under high

 power microscope. The term amorphous is used to describe complete lack of crystallinity. The

mineral lacks the outer geometric form the term massive is used. Slow cooling few centers of 

crystallization  big crystals with common orientation. Rapid cooling many centers of 

crystallization randomly oriented small crystals.

Some of the common minerals in which crystal form is especially diagnostic are quartz, halite,

garnet, fluorite, pyrite, galena, amphibole and pyroxene. Remember, however, that two or more

different minerals may have the same internal structure and may develop similar crystals.

Example: halite (made from sodium and chlorine) and galena (made from lead and sulfur) share

the same cubic crystal structure.

Some minerals have the same chemical formula, but they are different minerals by virtue of their 

different crystal structures. Each crystalline form represents a separate mineral species. Ex:

diamond ( C ) and graphite ( C).

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CLEAVAGE - Orientation and number of planes of weakness within a mineral. Directly

reflects the orientation of weak bonds within the crystal structure. This feature is also highly

diagnostic.

So, cleavage results from planes of weakness within the crystal structure along which the crystal

 break. If definite planes of weakness exist, the mineral will cleave or break , along the planes of 

weakness much more easily than in other directions. The surface along which the break 

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develops is referred to as the cleavage plane, and the orientation of the plane is the cleavage

direction.

  One Directional Cleavage peels in layers much like taking individual cards off a deck.

Mica is a good example of this type of cleavage.

  Two Directional Cleavage breaks along two directions at right angles. Feldspar is a good

example of this type of cleavage. Another two directional cleavage which shows not at right

angles. Example: amphibole. 

  Three Directional not right angles is often very easy to see.

  The mineral seems to have three dimensional boxes that would break if dropped. Calcite

is a good example of this type of cleavage. Another mineral which shows cleavage in

three directions at right angles. Example: halite. Cleavage in four directions (Octahedral

Cleavage) is complex cleavage. This cleavage is often hard to see in some mineral

samples containing it. A good example of this type of cleavage is the mineral Fluorite.

Fracture

Fracture is a mineral property where the atomic bonding between atoms in the crystal structure is

 perfect with no weakness. When these minerals are stressed they shatter making no two pieces

truly the same. There are two basic types of fractures, Conchoidal and Non-Conchoidal

(irregular).

  Conchoidal Fractures are easy to spot. They have a circular pattern in their break are

much like broken bottle glass. Obsidian is a good example of this mineral property.

   Non-Conchoidal Fracture minerals are also easy to identify. They have no directional

cleavage planes or swirls in there structure. A good example of this is the mineral Quartz.

HARDNESS - This is the resistance of the mineral to abrasion or scratching. This property

doesn't vary greatly from sample to sample of the same mineral, and thus is highly diagnostic. It

also is a direct reflection of the bonding type and internal atomic arrangement. A value is

obtained by comparing the mineral to a standard scale devised by Moh, which is comprised of 

10 minerals ranging in hardness from talc (softest) to diamond (hardest).

Moh’s Hardness scale:

1.  Talc 2. Gypsum3. Calcite 4. Fluorite

5. Apatite 6. Feldspar 

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7. Quartz 8. Topaz

9. Corundum 10. Diamond

On the Mohs scale, graphite (a principal constituent of  pencil "lead") has a hardness of 1.5; a

fingernail, 2.2 – 2.5; a copper penny, 3.2 – 3.5; a pocketknife 5.1; a knife blade, 5.5; window glass

 plate, 5.5; and a steel file, 6.5. A streak plate (unglazed porcelain) has a hardness of 7.0. Using

these ordinary materials of known hardness can be a simple way to approximate the position of a

mineral on the scale.

The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz

(8), but diamond (10) is four times as hard as corundum. The table below shows comparison with

absolute hardness measured by a sclerometer, with pictorial examples

Mohshardness  Mineral  Chemical formula  Absolute hardness

 by Knoop 1  Talc Mg

3Si

4O

10(OH)

2  1 

2  Gypsum CaSO4·2H

2O  32

3  Calcite CaCO3  135

4  Fluorite CaF2  163

5  Apatite Ca5(PO

4)

3(OH – ,Cl – ,F – )  430

6  Orthoclase

Feldspar 

KAlSi3O

8  560

7  Quartz SiO2  820

8  Topaz Al2SiO

4(OH

 – 

,F – 

)2  1340

9  Corundum Al2O

3  1800

10  Diamond C  7000

COLOR  

The color of a mineral is the result of a reflection, transmission, refraction and dispersion of 

light as it interacts with mineral’s chemical and structural components. Basing on the color the

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minerals are grouped into two: 1) Idiochromatic: minerals characterized by constant shade of 

color are said to be idiochromatic. Ex: Azurite ( always shows blue), olivine (green), Sulfur 

(yellow) and Galena (grey).2. Allochromatic: Minerals are characterized by colors that vary from

one specimen to another or even within the same specimen. The color is strongly influenced by

composition, impurities and /or defects. Ex; quartz shows different colors. Color should be

considered in mineral identification but should never be used as the major identifying

characteristic.

STREAK  is the color of the mineral powder and is typically obtained by scratching a mineral

specimen on an unglazed porcelain plate called a streak plate. Since most streak plates have a

hardness of about 6.5, only minerals that are somewhat softer than 6 will leave a powder when

scratched on the plate. Harder minerals will not leave a powder on the plate but can be powdered

 by other means.

When a mineral is powdered, it usually exhibits a much more diagnostic color than when it

occurs in large pieces. The color of the powdered mineral is referred to as streak. Commonly, a

mineral’s streak will be different from the color seen in hand specimen. Some minerals possess a

characteristic colored steak for example hematite possess a diagnostic brick-red streak. This is because

hematite absorbs nearly all wavelengths of light except for a narrow band in the red part of the

spectrum. Similarly, azurite shows blue streak because it transmits blue wavelengths while absorbing

the red and yellow parts of spectrum.

LUSTER 

Luster is the appearance of a mineral surface in reflected light, when looking at a macroscopic

specimen is principally the result of the amount of light reflected from its surface, the scattering

of light from the surface, and the amount of light absorbed by the mineral. These three variables

controls different luster's possessed by minerals.

The different types of luster referred to are:Metallic luster: strictly belongs to opaque minerals, where light is completely reflected from the

surface. Most of the ore minerals having high content of metals shows metallic luster. Eg.,

Galena, Magnetite, Pyrite, Chalcopyrite.

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Non-metallic luster: other luster types are collectively known as non-metallic luster. It may

 be brilliant or faint where reflection is poor which is due to scattering of light from the

mineral surface.

Adamantine: an exceptionally brilliant luster shown by minerals having very high  RI. Eg.,

Diamond, Zircon, Corundum (Ruby, Sapphire). These minerals are used as valuable gem stones.

Vitreous: shown by broken glass. Eg., Silicates (Q, Feld), Carbonate (Cal) with relatively low

RI.

Resinous: shown by resins. Eg., Sphene, S.

Greasy: shown by oily glass. It results from light scattered by a microscopically rough

surface. Eg. Nep (due to surface hydration having different RI), massive Quartz.

Pearly: pearl-like. It is due to reflection from successive layers, such as cleavage surfaces. Eg.,

Talc, Muscovite.

Silky: silk-like. It is due to the reflection from fibrous structure of minerals. Eg. Gypsum,

Asbestos, Malachite.

Earthy: luster of a surface from which there is little or no reflection. It is due to the porous and

fine-grained nature of mineral. Eg., Lim, Kaolinite.

TENACITY 

The resistance that a mineral offers to breaking, crushing, bending, cutting, drawing or tearing is

its tenacity. It is mineral's cohesiveness.

1. Brittle: A mineral that breaks and powders easily (Sulfides, Carbonates, Silicates and

Oxides),

2.Malleable: A mineral that can be hammered out without breaking, into thin sheets. They are

 plastic (Native metals),

3. Sectile: A mineral that can be cut with a knife into thin shavings (talc),

4. Flexible: A mineral that bends but retains it bent form. Does not resume its original shape  

 permanent deformation (Asbestos, clay minerals, Chlorite, Talc, gypsum)

5. Elastic: A mineral that after bending springs back and resumes its original position.

(Muscovite or biotite).

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DENSITY - Defined as the mass divided by the volume mass/volume; SI units are: kg/m3

or kg

m-3

, but geologists often use g/cm3

. Galena with density of 7.5, pyrite 5, quartz; feldspar, and

calcite between 2.6 and 2.8.

SPECIFIC GRAVITY - Ratio of the mass of a substance to the mass of an equal volume of 

water. Note that r water  = 1 g cm-3

. S.G. is unit less. Examples - quartz (SiO2) has a S.G. of 2.65

while galena (PbS) has a S.G. of 7.5 and gold (Au) has a S.G. of 19.3.

TRANSPARENCY

A mineral transmits light can be observed in hand specimens. These minerals are described as:

Transparent: objects are visible when viewed through the mineral Example: quartz, calcite and

 biotite.

Translucent- light is transmitted through the mineral, but not an image . Ex: gypsum

Opaque- no light is transmitted, even on the thinnest specimen edges ex: magnetite or pyrite.

OTHER PROPERTIES

Reaction to Hydrochloric acid: Calcite is one of the most common minerals of earth’s surface,  

when treated with dilute HCl,it will bubble vigorously. Dolomite , a mineral similar to calcite

will react with cold dilute HCl, but only if the specimen is powdered.

Magnetism: Magnetite is one of the few minerals to show obvious magnetic attraction.

Taste: The salty taste of halite is a definite and unmistakable property of that mineral

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