Rocks in the Forms of Minerals

Minerals is the naturally occurring inorganic solids, which posses a definite internal structure and specific chemical composition. Rocks (igneous, metamorphic, and sedimentary) consist of one or more minerals (e.g. mineral: calcite; rock: limestone). There are more than 3,500 elements identified, among it the eight most common elements forming mineral: oxygen, silicon, aluminium, iron, calcium, sodium, potassium, and magnesium.

Minerals example such as gold, syntactic diamonds, petroleum, steel, animal bones and so much more.

Minerals Group
Silicon + Oxygen = Silica (Quartz SiO₂ is pure silica)

Minerals containing silica = silicates minerals (Olivine Mg₂Fe₂SiO₄ and Orthoclase KAlSi₃O₈).

Two sub-groups of silicate mineral:

1. Ferromagnesian silicates: (dark color, more dense).
2. Non-ferromagnesian silicates : (light color, lesser dense)

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

Minerals Gallery:

How are Minerals Identified:
Color
Color is generally the most obvious properties (reliable diagnostic properties) of a mineral. Some minerals have a distinctive color which can be used in identification of minerals. In contrast, other minerals may exhibit a wide range of color among specimens. E.g. – impurities of quartz give variety color (pink, purple, milky white).

Cleavage

No.	Direction	Classification	Mineral
15	1 direction	Basal	Mica
16	1 directions at nearly right angle	Pinacoidal	Feldspar
17	2 directions at 124° and 56°	Prismatic	Amphibole
18	3 directions at right angle of each other	Cubic	Halite (rock salt)
19	3 directions not at right angle of each other	Rhombohedral	Calcite
20	4 directions	Octahedral	Fluorite

In crystal structure of mineral, some bonds are weaker than others. Cleavage is the tendency of mineral to cleave or break along weak bonding (when stressed). Cleavage can also be identified by distinctive smooth surface that are produced when the mineral is broken.

Fracture

No.	Fracture	Mineral
21	Even	Lithographic Limestone
22	Uneven	Serpentine
23	Conchoidal	Obsidian
24	Sub- Conchoidal	Rose Quartz
25	Splintery	Tremolite
26	Hackly	Copper

Many minerals do not break with flat cleavage surfaces. If they have one or two cleavage directions, they may break into another direction that does not leaves a flat surface. This irregular break, other than cleavage, is known as fracture.

Luster

Kind of Luster
Metallic:
27	Metallic	Pyrite
Non- Metallic:
28	Adamantine	Sphalerite
29	Vitreous	Rock Crystal
30	Resinous	Sulphur
31	Greasy	Nepheline
32	Pearly	Talc
33	Silky	Gypsum (satin spar)
Degrees of Luster
34	Splendent	Micaceous Hematite
35	Shining	Calcite
36	Glistening	Prochlorite
37	Submetallic	Ilmenite
38	Dull	Chalk

Luster minerals normally appearance in reflected light that is different from its inherent colors. Two types of luster minerals:

• Metallic luster – minerals that have appearance in metals.
• Non-metallic luster – glassy, dull, silky.

Hardness
Hardness of minerals is the measure of the resistance of a mineral to abrasion or stretching. It is determine by rubbing the mineral to identified against another mineral of known hardness.

Specific Gravity
Compares the weight of a mineral to the weight of an equal volume of water.
E.g. – 1 cm³ of a mineral weights 3 times as much as 1 cm³ of water; S.G. = 3
So, S.G. of pure 24 karat gold = 20.

For further reading on minerals of rock, proceed via Wikipedia. The gallery above – credit and reference from Ward’s Natural Science.

Read More Constructive Posts:

• 2 Category of Rock Testing
• The Three Groups of Rock
• Rock Mechanics in Civil Engineering

Tagged as: Rock and Testing

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