Chapter 2 - Minerals_prt

8/10/2019 Chapter 2 - Minerals_prt

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CHAPTER 2:

MINERALS


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INTRODUCTION

From the earliest time, man has found important uses ofminerals.

E.g. clay for bricks and pottery; quartz and jade forweapons, garnet, amethyst and other coloured stones

for ornaments and also gold, silver and copper forornaments and utensils.

The rocks and soils that are made from minerals.

Thus, knowledge of mineralogy is important.


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In civil engineering, the study of minerals is important because:

The minerals, rocks, and soils are the materialswith whichthe civil engineer must deal.

In the designing of any civil structure, engineers must beable to distinguish and evaluate natural materials presentat site.

Minerals are responsible for the physical and mechanicalproperties of rock and soil.

In industry, minerals are directly incorporated into chemicals,abrasives, and fertilizers and are processed into thousands of

other useful products.


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The Nature and Origin of Minerals Mineralsare formed in various ways and different conditions.

Some minerals require a million of year to form and some just a few hours.

The mineral formations takes places either in the molten rock or magma, nearthe Earth surface or deep in the Earth crust as a result of transforming.

What is a mineral?

They occur naturally as inorganic sol ids.

They have a speci f ic internal st ructure; that is, their atoms are preciselyarranged into a crys tal l ine sol id.

They have a chemical com pos i t ion that varies within definite limits and canbe expressed by chemical formula.

They have definite set of phy sical propert ies (hardness, cleavage, crystal formetc) that result from their crystalline structure and composition.


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Physical Properties of Minerals

The minerals can be identified by their physical properties.

The physical properties can be observed by simple tests:

(a) Color

(b) Streak(c) Cleavage and fracture

(d) Luster

(e) Hardness

(f) Density and specific gravity(g) Reaction with acid


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Color

The color of the mineral = seen by eye.

Color results from a minerals chemical composition,impuritiesthat may present in the sample, flawsor damagein the internal structure, the light in the room or strongreflective surfaces.

Unfortunately, even though color is the easiestphysicalproperty to determine, it is not the most usefulin helping tocharacterizea particular mineral.

The problem is some minerals display a rainbow of colors(shown by the mineral fluorite (CaF2) ).

Therefore, colour is a general rather than specificindicator. Quartz, for example, ranges through the spectrum

from clear, colourless crystals to purple, red, white, grey andjet black.


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The many colors of fluorite


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Streak

Streak- color of finely powdered mineral particles produced byscraping the specimen along a roughened surface (streak plate).

The mark left behind can be a characteristic feature of themineral.

The streak is not necessarily the same as the color of themineral, for example hematite (metallic grey) produces a reddishbrown streak.

The limitation of a streak plate is that it can only be used on

minerals with a hardness less than seven.

The combination of luster, color, and streak may be enough topermit identification of the mineral.


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Cleavage and fracture

There are two ways in which a mineral can breakalong cleavage andfracture.

Cleavage planessome atomic bonds are weaker

than others. Mineral tend to break along planes ofweak bonding. Eg mica has cleavage (weakbonding) in one direction.

Fractureatomic bonds are equally strong in alldirections, thus when mineral break, most produceirregular surface.


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Examples of Cleavage Fracture


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Luster Luster The quality of light is reflected from the surface of a mineral.

Luster is described in terms of the degree of brightness.

The terms to describe luster are :

Metallic lusterthe minerals that have the appearance of metals e.g. galena and

magnetite (Iron Ore).

Sub-metallicsome metallic minerals when exposed to the atmosphere developcoating, not shiny as freshly broken surfaces.

Non-metallic luster

1. Vitreous Lustera mineral having a glassy shine. E.g. Quartz and Calcite.2. Admantine lustreThe mineral having a diamond like shine. E.g. Diamond and Zircon

3. Pearly Lustrea mineral having a pearly shine. E.g. Muscovite.

4. Silky lustrea mineral with a silky shine. E.g. Asbestos.

5. Resinious lustrea mineral with a greasy shine like resin. E.g. Talc.


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Transparency

Transparency is ability to transmit light.

The transparency may be either opaque, translucent, or transparent.

Type of Transparency:

Opaque When no light is transmitted the mineral. E.g. Orthoclase, Magnetite AndHornblende.

Transparent - When allows both light and image are visible through the mineral. E.g.colourless Quartz and calcite.

TranslucentWhen allows light, but not an image, is transmitted through the mineral. E.g.milky white varieties Quartz and Calcite.

Semi Transparent

Mineral which allows light pass partially and objects are seen hazythrough the mineral. E.g. Slightly milky white varieties Quartz and Calcite.


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Contd

Transparent - Quartz

Semi Transparent- Sulfur


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Hardness

Hardnessis a measure of a mineral's resistance toabrasion.

In case of mineral identification, hardness is a relative scalethat refers to the di f f icu l ty of s cratch ing the mineral.

The hardness is described using an arbitrary scale of tenstandard minerals.

The scale is called the MOH's scale of hardness.

The hardness of any object is controlled by the strength ofbonds between atoms and is measured by the ease ordifficulty with which it can be scratched.


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Reaction with acid

When dilute hydrochloric acid (typically

10%) is dripped onto some minerals a

reaction takes place.

On calcite (CaCO3), bubbles of carbon

dioxide are produced; in some iron

sulphide ores, hydrogen sulphide is

produced.


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Density and specific gravity

Density is weight per unit volume, kg/m or

g/cm.

Specific gravity (SG) is the ratio of its weight to

the weight of an equal volume of pure water at4C.

SG of galena is 7.8 and its density is 7.8 g/cm.

Gold density is 19.3 g/cm.

SG of diamond is 3.5.

SG of graphite between 2.09 and 2.33.


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Silicate Mineral

What are silicate minerals?

A group of minerals contains SiO44-as the dominant

polyanion.

In these minerals the Si4+cation is always surrounded by 4oxygensin the form of a tetrahedron.

Because Si and O are the most abundant elements in theEarth, this is the largest group of minerals and is divided intosubgroups based on the degree of polymerization of the SiO

4

tetrahedra.

Approximately 30% of all minerals are silicates and somegeologists estimate thatthe crust has been about 95%silicate minerals, of which some 60% is feldspar and 12%

quartz.


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Structure and Classification of the Silicates

In all silicate structures investigated, the silicon atomsare in fourfold coordination with oxygen.

The bonds between siliconand oxygenare so strong

that the four oxygen are always found at the cornersof a tetrahedron of nearly constant dimensions andregular shape.

Hence the existenceof a silicon tetrahedron will make

a mineral as a silicate mineral and its absencewillmake it as a non-silicate mineral.


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The silicon-oxygen tetrahedron is the basic building block of the silicate

minerals. This is the most important building block in geology because it

is the basic unit for 95% of the minerals in the crust


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Silicate classification is based on the following

types of linkages:

1. Single chainspyroxene

2. Double chains

amphiboles

3. Two dimensional sheets minerals - micas,

chlorites, and clay minerals.

4. Three dimensional frameworks - feldspar and

quartz


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Silicon-oxygentetrahedral

groups can

formed in single

chains, doublechains and

sheets by sharing

of oxygen ions

among silica ions


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Rock Forming Minerals

Common minerals found in the rocks.

Minerals vary greatly in their chemical composition andphysical properties.

Before we begin the study of rocks it is necessary toknow the chief rock forming minerals.

Although there are more than 2000 known minerals,only a few are abundant in the most common rockforming minerals and can be identified by its physicalproperties by simple tests.

Minerals are classified according to chemicalcomposition and structure.


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Oxygen and Silicon make up approximately 75% ofweight of rocks.

Siliconand Oxygenoccur on combination with otherabundant element to form silicate minerals.

This group is called the silicate group because all itsmembers contain a specific structural combination ofsilicon and oxygen, even though most silicateminerals also contain other elements.

Thus silicate minerals is the chief rock formingminerals.


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Examples of rock forming

minerals


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Quartz

Most common of silica group minerals.

Crystallization from the magma took place below 867C and stablepractically over the whole range of geological conditions.

Present in silica-rich igneous rocks both volcanic and plutonic andcan be recognized by glassy grains of irregular shape withoutcleavage.

Stable both physically and chemically, therefore difficult mineral toalter or breakdown once formed.

Important constituent in most metamorphic rocks, usually colourlessor white, but can occur in practically any shade, glassy luster.

Can be utilized in construction industry.


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Quartz Mineral


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Feldspar group

Most important group, abundant and constitute the mostof rock forming minerals.

Make up to 60% of the earth's crust Found almost on all

of the igneous rocks, in some sedimentary and manymetamorphic rocks.

Two major types of feldspar: Potassium feldspar (K-

feldspar) and Plagioclase feldspar.

Good cleavage in two directions, porcelain luster andhardness of 6.


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Contd

The plagioclase feldspars: Albite, (Sodium aluminum silicate)

Oligoclase, (Sodium calcium aluminum silicate)

Andesine, (Sodium calcium aluminum silicate)

Labradorite, (Calcium sodium aluminum silicate)

Bytownite, (Calcium sodium aluminum silicate)

Anorthite, (Calcium aluminum silicate)

The K-feldspars or alkali felspars: Microcline, (Potassium aluminum silicate)

Sanidine, (Potassium sodium aluminum silicate)

Orthoclase, (Potassium aluminum silicate)
http://mineral.galleries.com/minerals/silicate/albite/albite.htmhttp://mineral.galleries.com/minerals/silicate/oligocla/oligocla.htmhttp://mineral.galleries.com/minerals/silicate/andesine/andesine.htmhttp://mineral.galleries.com/minerals/silicate/labrador/labrador.htmhttp://mineral.galleries.com/minerals/silicate/bytownit/bytownit.htmhttp://mineral.galleries.com/minerals/silicate/anorthit/anorthit.htmhttp://mineral.galleries.com/minerals/silicate/microcli/microcli.htmhttp://mineral.galleries.com/minerals/silicate/sanidine/sanidine.htmhttp://mineral.galleries.com/minerals/silicate/orthocla/orthocla.htmhttp://mineral.galleries.com/minerals/silicate/orthocla/orthocla.htmhttp://mineral.galleries.com/minerals/silicate/sanidine/sanidine.htmhttp://mineral.galleries.com/minerals/silicate/microcli/microcli.htmhttp://mineral.galleries.com/minerals/silicate/anorthit/anorthit.htmhttp://mineral.galleries.com/minerals/silicate/bytownit/bytownit.htmhttp://mineral.galleries.com/minerals/silicate/labrador/labrador.htmhttp://mineral.galleries.com/minerals/silicate/andesine/andesine.htmhttp://mineral.galleries.com/minerals/silicate/oligocla/oligocla.htmhttp://mineral.galleries.com/minerals/silicate/albite/albite.htm


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Feldspar Mineral

Albite Oligoclase

Andesine Anorthite
http://mineral.galleries.com/minerals/silicate/albite/albite.htmhttp://mineral.galleries.com/minerals/silicate/oligocla/oligocla.htmhttp://mineral.galleries.com/minerals/silicate/andesine/andesine.htmhttp://mineral.galleries.com/minerals/silicate/anorthit/anorthit.htmhttp://mineral.galleries.com/minerals/silicate/anorthit/anorthit.htmhttp://mineral.galleries.com/minerals/silicate/andesine/andesine.htmhttp://mineral.galleries.com/minerals/silicate/oligocla/oligocla.htmhttp://mineral.galleries.com/minerals/silicate/albite/albite.htm


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Mica

Micas are a group of monoclinic minerals and arecharacterized by perfect cleavage.

Typically paper thin, shiny, elastic cleavage plates.

Only two common occurring mica known as biotite (darkbrown to black), usually less commercial value andmuscovite (colourless or slightly tinted).

Abundant in granite and in many metamorphic rocks andis also a significant component of many sandstones.


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Pyroxene

High temperature minerals found in many

igneous and metamorphic rocks.

Usually dark coloured (dark green to

black) and contains silicates of iron and

magnesium.

Occurs in basic and ultrabasic rocks.


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Olivine

Occurs chiefly in basic and ultrabasic rocks with (MgFe)2SiO4

present.

Crystallizes at a high temperature, over 1000oC, one of

the first minerals to form from basic magmas, andcommon in basalt.

The only mineral clearly visible in the hand specimen.

Probably the major constituent of the material beneaththe Earth's crust.


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Amphiboles

This mineral has much in common with pyroxenes andconsist of complex silicates which are magnesium,calcium and iron.

Hornblende the most abundant amphibole is a commonconstituent ofigneous and metamorphic rock.

Colour ranges from green to black.

Common in metamorphic rock known as amphibolite.


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Calcite

Composed ofcalcium carbonate (CaCO3) and principal mineral oflimestone.

Can be precipitated directly from seawater and removed from it byorganisms to make shells.

Dissolved in groundwater and reprecipitated as new crystals incaves and fractures in rock.

Soft (3.0) and easy to scratch, effervesces (bubbles) in dilutehydrochloric acid, perfect cleavage in three directions but not at right

angle.

Major component of limestone and major mineral metamorphic rock,marble.


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Dolomite

Composed of magnesium and carbonate (CO2).

Widespread in sedimentary rocks, forming when

calcite reacts with solutions of magnesiumcarbonate in seawater or groundwater.

It will effervesces in dilute hydrochloric acid onlyif it is in powdered form.


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Clay minerals

Constitute major part of the soil and thus

encountered more frequently than other

minerals.

Form when air and water interact with the

various silicate minerals breaking them to

form clay and other products.


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Halite and Gypsum

Two most common minerals formed by the

evaporation of seawater or saline lake water.

Halite (common salt, NaCI) easily identified byits taste, very soft and scratched easily with

finger nail.

Gypsum composed of calcium sulphate and

water (CaSO42H2O).


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Chlorite (MgFe)5Al(Si3AI)O10(OH)8

A green flaky minerals formed by hydrous

silicates of magnesium and aluminum.

Found in igneous rocks and in

metamorphic rocks such as chlorite-schist

and in some clays.


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Serpentine Mg6Si4O10(OH)8

An alteration of olivine, pyroxene or

hornblende.

Change from olivine to serpentine may be

brought about by action of water and

silica.

Found in basic and ultrabasic rocks.


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Talc Mg3Si4O1O(OH)3

Soft flaky mineral, white or greenish white, easilyscratched by finger nails.

Occurs as a secondary product in basic and ultrabasicrocks and in talc-schist.

Kaolin (China Clay) AI4Si4O10(OH)8

Derived from breakdown of feldspar by action of waterand carbon dioxide.

White or grey, soft with texture of flour and clayey smell

when damp.


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Non Silicate Minerals Refer Table 2.0 for common, economically important non-silicate mineral.

Oxides and Hydroxides:

These are minerals that are form by combination of various cations withoxygen.

Some examples of this type of minerals are hematite, ilmenite, magnetite,Bauxite, Limonite and Cassiterite.

Carbonates and Sulfates:

Consist of framework similar to the silica tetrahedra.

An important mineral in this group is gypsum, the main ingredient inbuilding materials.

The most important carbonate minerals are calcite which combines calciumwith the carbonate ion, and dolomite which contains calcium andmagnesium in its structure.


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Halides:

Often occurring as chemical deposited

sedimentsformed by evaporation and as

vein minerals in igneous rocks.

Example of halide mineral is halite or rock

salt deposit from the evaporation of

enclosed bodies of salt water.

Table 2.0: Examples of important non-silicate minerals


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Table 2.0: Examples of important non silicate minerals


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Minerals which make up the three broad categories of rocks

Igneous rocks

quartz, biotite, muscovite, amphiboles

(e.g. hornblende), pyroxenes (e.g.

augite), orthoclase, olivine

Sedimentary rocks

parent igneous rocks - quartz and

feldspar the earth's surface minerals -clay minerals, hydrous aluminum

silicates, carbonates, calcite and

dolomite, those deposited from saline

waters - rock salt and gypsum

Metamorphic rocks quartz, feldspar, amphiboles,pyroxenes, micas, garnet chlorites, the

carbonates metamorphosed limestone

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