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CHAP 3.1 Rocks versus minerals Minerals naturally occurring inorganic solids,which posses a definite internal structure andspecific chemical composition. Rocks consist of one or more minerals.

- e.g . mineral : calcite; rock : limestone. > 3500 element identified, 8 most commonelements forming mineral:

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Table1: Composition of element in earths crust

Element Symbol % of earths crust

Oxygen O 49.52

Silicon Si 25.75

Aluminium Al 7.51Iron Fe 4.70

Calcium Ca 3.39

Sodium Na 2.64

Potassium K 2.40

Magnesium Mg 1.94

Total % 97.85

% of other elements 2.15

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pink chalcedony

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sulphur

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Azurite

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Flourite

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Minerals Minerals naturally occurring inorganic solids,which posses a definite internal structure andspecific chemical composition. Gold is mineral. Syntactic diamonds are minerals. Petroleum is mineral. Animal bone is mineral. Steel is mineral.

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CHAP 3.1 Mineral group Silicon + oxygen = silica (Quartz SiO2 is pure silica) Minerals containing silica = silicates minerals(Olivine Mg2Fe2SiO4 & Orthoclase KAlSi3O8). 2 subgroups of silicate mineral:

Ferromagnesian silicates: (dark color, > dense).Nonferromagnesian silicates : (light color, < dense)

Carbonate mineral , (CO3)-2 :- minerals calcite (CaCO3) : limestone.- mineral dolomite (CaMg(CO3)2)

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Silicate minerals

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Carbonate minerals

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CHAP 3.1 How are minerals identified1. Color .2. Cleavage.

3. Luster.4. Hardness (Mohs hardness scale).5. Specific gravity.6. Other useful minerals properties.

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CHAP 3.1Color

Unreliable diagnostic properties.

E.g.impurities of quartz give variety color (pink,

purple, milky white).

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Table 3: Dark-coloured mineral silicates & their

typical physical propertiesMineral Colour SG Hardness Cleavages

Olivine Green/darkgreen

3.5+ 6.5 None (poorfracture)

Pyroxene

(augite)

Black/brown 3.3 5.5 2

Hornblende Black 3.3 5.5 2

Biotite Brown 3 2.5 1 (perfect)

Garnet Red (variable) 3.5+ 7 None

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Table 4: Light-coloured mineral silicates & their

typical physical properties

Mineral Colour SG Hardness Cleavages

Feldspars White, pink, variable 2.7 6 2

Clays White 2.6 2

2.5 1 perfectQuartz Colourless, white, red,variable

2.65 7 None

Muscovite Colourless 2.7 2.5 1 perfect

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CHAP 3.1 Cleavage In crystal structure of mineral, some bonds are

weaker than others.

Cleavagetendency of mineral to cleave or breakalong weak bonding (when stressed) .

Cleavage can be identified by distinctive smooth

surface that are produced when the mineral isbroken.

Fracturemineral not exhibit cleavage.

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Figure 1: Cleavage in minerals

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Cleavage in mineral biotite (mica): 1 direction

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Cleavage in mineral calcite : 3 direction

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Serpentine (Asbestos) : fibrous fracture

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Quartz: choncoidal fracture

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Bornite : irregular fracture

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CHAP 3.1 Luster Luster - appearance in reflected light. Metallic lusterminerals that have appearance

in metals.

Nonmetallic lusterglassy, dull, silky.

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Figure 2: Luster appearance.

Fig 2.15a - 44

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CHAP 3.1 Hardness Measure of the resistance of a mineral to

abrasion or stretching.

Determine by rubbing the mineral to identifiedagainst another mineral of known hardness.

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Table 2: Mohs Hardness Scale

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CHAP 3.1 Specific gravity Compares the weight of a mineral to the weight

of an equal volume of water.

E.g.

1cm3

of a mineral weights 3 times as muchas 1cm3 of water; S.G. = 3

S.G. of pure 24 karat gold = 20.

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Figure 3: Various minerals properties.

Fig 2.19a - 47