2.1. THE ROCK FORMING MINERALS

Even with the 5000 known mineral species, most of the rocks are formed from the fusion of few common minerals. These minerals are called rock-forming minerals.

The different rock-forming minerals are:

1. Feldspars
2. Quartz
3. Amphiboles
4. Micas
5. Olivine
6. Garnet
7. Calcite
8. Pyroxenes

There are still other minerals within rocks but they occur in minute quantities. They are referred to as accessory minerals. Although they have negligible amount, they can provide a character or insight in the history of the rock, specifically its age.

The different accessory minerals are listed below:

1. Zircon
2. Monazite
3. Apatite
4. Titanite
5. Tourmaline
6. Pyrite and other opaques

2.1.1. FELDSPAR GROUP

Considered as the most abundant of all minerals, they are used for making more than half (50%) by weight of the Earth's crust. They are non-metallic and silicate minerals.

PHYSICAL PROPERTIES:

CRYSTAL SYSTEM: monoclinic,triclinic

HABIT: Tabular (crystalline)

CLEAVAGE: Perfect( 2- directional)

VARIETIES OF POTASH

• Orthoclase
• Sanidine
• Microcline

SODA LIME FELDSPAR

• Albite
• Oligoclase
• Andecine
• Amarthitie
• Labrodorie

USES:

After extraction from rocks, feldspar is crushed into fine powder or granules, which are used in the manufacturing of the following:

• Ceramic tiles
• Glass plates
• Pottery
• Paint
• Plastics
• Fiberglass insulation

2.1.2. QUARTZ GROUP

Quartz is an important rock-forming mineral next to feldspar. It is a silicate group; it is a non-metallic refractory mineral.

PHYSICAL PROPERTIES:

CRYSTAL SYSTEM: Hexagonal HABIT: Crystalline or amorphous

FRACTURE: Conchoidal

HARDNESS: 7

SPECIFIC GRAVITY: 2.65-2.66(LOW)

STREAK: No

TRANSPARENCY: Transparent/semi-transparent/opaque

POLYMORPHISM TRANSFORMATION: Quartz ,tridymite,crystotallite,melt

VARIETIES IN COLOR:

Pure quartz is always colourless and transparent. The mineral shows color due to the presence of impurities, such as:

• Milky quartz: light brown, pure white, opaque
• Rose quartz: rose
• Smoky quartz: shades of grey
• Amethyst: purple or violet

USES:

1. Quartz is used in our daily activities. Soap, toothpaste, paint, rubber, caulking compounds, sandpaper, flux in the smelting process, time devices such as watches and clocks, electronic devices like cell phones, televisions, lasers and computers have quartz as a vital component.

2. A pure quartz produces an electrical voltage when put under pressure. This feature meant that the mineral is able to be used in communication, time pieces and other electronic items.

3. Quartz sand is used on golf courses, volleyball courts, children's sand boxes, baseball fields, and is used to replenish depleted beaches. It is also used for sand blasting, grit for sawing and sanding and scouring cleansers.

4. Quartz is used in the construction industry as concrete aggregate and as sand in mortar and cement.

2.1.3. PYROXENES GROUP

Another importatn rock-forming mineral are the pyroxenes which occur in dark colors - igneous and metamorphic rocks. They are rich in calcium, magnesium, iron, and silicates. They show a single chain structure of silicate. Based on the internal atomic structure, this group is classified into Orthopyroxene and Clinopyroxene.

PHYSICAL PROPERTIES:

CRYSTAL SYSTEM: Monoclinic

HABIT: Crystalline

CLEAVAGE: Good ( primastic cleavage)

FRACTURE: Conchoidal

COLOUR: shades of greyish green and black

LUSTRE: vitreous

HARDNESS: 5-6

SPECIFIC GRAVITY: medium

STREAK: white

OCCURRENCE: ferro magnesium mineral of igneous rock (dolerite)

TRANSPARENCY: Translucent/opaque

USES:

Jade ornaments and figurines fashioned by ancient Aztec and Mayan artisans are pyroxene's most familiar face.

2.1.4. AMIPHOBLE GROUP

This group is closely related to the pyroxene group. These minerals show double chain silicate structure. They are rich in calcium, magnesium, iron oxide, manganese, sodium, potassium and hydrogen.

CLASSIFICATION:

1. Orthorhombic
2. Monoclinic

• Tremolite
• Actinolite
• Hornblende

USES:

1. Minerals under this group are used as paving stones and as veneer or facing on buildings (both for interior and exterior use).
2. They are also used as crushed stone for the casual crushed stone applications such as road and railroad bed construction.
3. Gemologists and lapidary workers have discovered that some amphibolite rocks produce a shimmer effect when it is polished. They use rounded and polished pieces of amphibolite for various pieces of jewelery.

2.1.5. HORNBLENDE GROUP

These minerals are members of the amphibole group with more complex silicates. They are usually called double chain silicates. 

PHYSICAL PROPERTIES:

CRYSTAL SYSTEM: Monoclinic

HABIT: crystalline

CLEAVAGE:

good(prismatic)

FRACTURE: conchoidal

COLOUR: dark green, dark brown black

LUSTRE: vitreous

HARDNESS: 5 to 6

SPECIFIC GRRAVITY: 3 to 3.5 (medium)

STREAK: colourless or white

USES:

1. Its primary use might be as a mineral specimen. Hornblende has been used to estimate the depth of crystallization of plutonic rocks.
2. They are crushed and used for highway construction and as railroad ballast.
3. They are cut and used as dimension stone. The highest quality pieces are cut, polished, and sold under the name "black granite" for use as building facing, floor tiles, countertops, and other architectural uses.

2.1.6. MICA GROUP

These minerals form sheet-like structure. They can be split into very thin sheets along one direction. These minerals are rich in aluminum and magnesium. The closest estimation shows that mica minerals occupy around 4% of the Earth's crust.

USES:

1. Mineral in mica family are used in paints as pigment extender and also helps to brighten te tone of colored pigments.
2. In the electrical industry such as thermal insulation and electrical insulators n electronic equipment.
3. The shiny and glittery appearance makes it important for toothpaste and cosmetics.
4. The high thermal resistance makes it to be a good insulator in various electronics.

2.1.7. OLIVINE GROUP

Olivine is found commonly in igneous rocs of low silica content, and occasionally found in metamorphic rocks

PHYSICAL PROPERTIES:

Hardness: 6.5-7
Specific gravity: 3.2-4.4
Transparency:  Transparent to translucent
Colour:  Yellowish green to green, also colourless, greenish brown to black
Streak:  White
Lustre:  Vitreous
Cleavage/fracture:  Imperfect / conchoidal
Crystal habit/mode of occurrence:  Prismatic (equant to elongate) / granular, massive

USES:

1. This mineral is used in metallurgical processes as slag conditioner.
2. Olivine containing high magnesium is added to blast surfaces to extract impurities from steel and then form a slag.
3. Olivine is also used as a refractory material. It is used to make refractory brick and used as a casting sand.

2.1.8. GARNET GROUP

Garnet is a more complex orthosilicate (than olivine, for example).

PHYSICAL PROPERTIES:

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 

USES:

1. The first industrial use of garnet is an abrasive.
2. In the US, garnet is used in waterjet cutting.
3. Granules are also used in abrasive blasting (also known as "sand blasting).
4. Granules are often used as a filter media.