Calcium Minerals: Calcium minerals are those minerals, which, somehow, contains calcium in their chemical composition. Some of the calcium minerals are as under:
(1). Calcite: CaCo3
- Crystal System: Hexagonal
- Cleavage: Calcite has perfect cleavage.
- Hardness: Calcite is a soft mineral, which has a hardness of 2 at Moh’s scale.
- Specific Gravity: The specific gravity of calcite mineral is 2.71.
- Lustre: Calcite has vitreous lustre.
- Colour: Calcite is, usually found in white colour, but in many case it is colourless, and transparent, gray, red, green, blue, yellow and brown.
- Habit: It has four common forms: tabular, prismatic, rhmbohedral and scalenohedral. Apart from these forms it is also found in fibrous, granular and stalactiteic forms.
Occurrence: The origin of Calcite may be igneous as in intrusive carbonatites, sedimentary such as limestone, and metamorphic such as marble. Calcite is commonly found in metallic ore veins and calcite veins are also found in various rocks.
Uses of Calcite: The important use of calcite is in the manufacturing of cement and lime. Calcite is also used as a flux in the smelting of ores and as a fertilizer.
(2). Aragonite: CaCO3
Physical Properties of Aragonite:
- Crystal system: Orthorhombic
- Cleavage: Aragonite has a distinct cleavage.
- Lustre: It has vitreous lustre.
- Hardness: Aragonite is a soft minerals with a hardness of 3.5-4 at Moh’s scale.
- Sp.Gr: Aragonite has a specific gravity 2.95.
- Colours: Aragonite is found in colourless look as well as in white, pale yellow, gray, and rarely in green or violet look.
- Habit: It is found in prismatic crystals, tabular and stalactite crystal form.
Occurrence: Aragonite is much less common if compared to calcite mineral. It is the main component of shells of many organisms. Aragonite occurs in some sedimentary deposits.
Uses of Aragonite:
- As the aragonite is the minor constituent of limestone, therefore, it is used in making lime and cement.
- Aragonite is used in the manufacturing of steel and ornamental and utensil carving.
(3). Dolomite: CaMg (CO3)2
Physical properties of Dolomite:
- Crystal System: Dolomite has a hexagonal crystal system.
- Cleavage: It has perfect rhombohedral cleavage.
- Hardness: Like calcite and aragonite, dolomite is not so hard. It has a hardness of 3.5-4 on Moh’s scale.
- Sp.Gr: Specific gravity of Dolomite is 2.85.
- Lustre: It has vitreous to pearly luster.
- Colours: Dolomite is found in white, yellow, brown, pinkish colours. It may also be found in a colourless look.
- Habit: The crystals of dolomite shows curved, granular and massive faces.
Occurrence: Dolomite occurs as extensive sedimentary beds. It is generally thought to be formed by the replacement of calcium carbonate of limestone by dolomite.
Uses of Dolomite:
- Dolomite is used as a building and ornamental stone.
- It is used as wall sheathing on the external walls in order to protect them from environmental effects.
- It is also used in the manufacturing of refractory bricks for furnace linings.
(4). Gypsum: CaSO4 + 2H2O
Physical Properties of Gypsum:
- Crystal System: Monoclinic
- Cleavage: Perfect
- Hardness: 2 on Moh’s scale
- Sp.Gr: 2.32
- Lustre: Usually gypsum has a vitreous lustre. But deposits of gypsum have a pearly and silky lustre.
- Colours of Gypsum: Gypsum is found white, grey, yellow, red, and pink colours.
- Habit: It is found in tabular and prismatic, massive, fibrous, and granular crystals.
- Varieties of Gypsum:
- Satin-spar is a fibrous gypsum with a silky lustre.
- Alabaster is a fine-grained massive variety.
- Selenite is a variety of gypsum that yeilds broad colourless and transparent folia.
Occurrence: Gypsum occurs as an evaporite deposite. It is also found as a secondary mineral, deposited from percolating groundwater.
Uses of Gypsum:
- Gypsum is used to make plaster of Paris.
- Gypsum is used as a fertilizer.
- Gypsum is used in manufacturing of H2SO4 (Sulphuric Acid).
- Gypsum is also used to reduce water logging and salinity.
- It is used as a filler in various materials.
(5). Anhydrite: CaSO4
- Crystal System: Anhydrite is an orthorhombic crystalline mineral.
- Cleave of Anhydrite: Perfect
- Hardness of Anhydrite: 3.0- 3.5
- Sp.Gr.: 2.89- 2.98
- Lustre: vitreous to pearly lustre.
- Colours: Anhydrite has white, gray, bluish, red colours but is sometimes colourless.
- Habit: Usually massive, fibrous and granular crystals. It is also found in concretionary form.
- Alteration: As the chemical formula of Anhydrite is CaSO4, therefore, by adding water to it, it converts into gypsum. Resultantly, the volume is also increased due to the addition of water to anhydrite.
Occurrence: Anhydrite is found in bedded evaporite deposits. Most of the deposits of anhydrite are throught to be secondary after gypsum.
Uses of Anhydrite:
- Like gypsum, it is also used as a fertilizer.
- Used in cement and plaster of Paris.
- Used in manufacturing of Sulphuric Acid.
- Anhydrite is used to reduce waterlogging and salinity in agricultural lands.
- Other uses of Anhydrite are the same as those of Gypsum.
(6). Fluorite: CaF2
Physical Properties of Fluorite:
- Crystal System of Fluorite: cubic
- Cleavage: Perfect octahedral
- Hardness: 4 on Moh’s scale
- Sp.Gr.: 3.18
- Lustre: Fluorite has a vitreous luster.
- Colours: Light green, yellow, bluish-green or purple, brown and white. It is also found in colourless look.
- Habit: cubic crystal, massive and granular.
Occurrence: Fluorite is commonly found in hydrothermal veins. It is found associated with galena and sphalerite. Fluorite also occurs in pneumatolytic tin veins and in some granites.
Uses of Fluorite:
- Fluorite is used as a flux in steelmaking and has other metallurgic uses.
- It is used in the preparation of Hydrofluoric acid.
- Fluorite is the biggest natural source of fluorine gas, thus it is used in the preparation of fluorine gas.
- Fluorite is used in the chemical and ceramic industry.
- Fluorite is used in lenses of cameras, telescopes, and microscopes.
- The gas (fluorine) used to prepare Uranium Hexafluoride, during the process of enrichment of uranium, is also obtained from fluorite.
(7). Apatite: Ca5 (PO4)3 (F, Cl, OH)
Physical Properties of Apatite:
- Crystal System: Hexagonal crystal system.
- Cleavage: Apatite has a poor cleavage.
- Hardness: 5 Moh’s scales
- Sp.Gr.: 3.15-3.20
- Lustre: Vitreous to resinous lustre.
- Colours: It is in blue, violet, and colourless looks, with some shades of green or brown.
- Habit: Long prismatic, tabular, massive and granular crystals.
Occurrence: Commonly found in all igneous rocks including pegmatites and hydrothermal veins. Apatite is also found in contact and regional metamorphic rocks and in sedimentary rocks.
Uses of Apatite:
- It is used as a source of phosphate in fertilizers.
- Used as a gemstone.
- Used in the preparation of Phosphoric Acid.
- It is also used as an animal food suppliment.
- It is also used in preparing elemental phosphate, and phosphate compound for industrial uses.