The mineral calcite is the major or sole constituent of most commercial
calcium carbonate products. These include natural limestone, marble, and
chalk, plus most precipitated calcium carbonate. Aragonite is a metastable
polymorph of calcite that typically has an acicular crystal shape. Natural
aragonite products are less common, but precipitated varieties are available.
Many calcium carbonate deposits are the remains of the shells and skeletons of ancient sea life. The color, purity, density, and crystal morphology depend upon the influence of waves and water currents before burial, and upon temperature, pressure, and tectonic activity after burial. The most common mineral impurities are quartz and clay. The most common substitutes for calcium are other divalent cations, such as magnesium, strontium, and barium, although the amount of substitution is usually no more than a few percent. The exception is magnesium, which can substantially replace calcium to form the mineral dolomite, CaMg(CO3)2. Calcium carbonate rocks, a common constituent of the Earth’s surface, range from high-calcium limestones containing >95% calcite to dolostones containing 90% or more dolomite.
Chalk is a fine-grained, white, friable, high-purity limestone. Marble is a
dense, hard, low porosity stone composed substantially or solely of calcium
carbonate. It is formed by the action of heat and pressure on buried limestone beds. Marble used for ground calcium carbonate products is chosen for color and purity. Marble for decorative and dimension stone (blocks, fascia slabs, tile) is selected for its characteristic shadings or veining, caused by minor mineral impurities, and for its ability to take a polish. Travertine is a banded, dense calcium carbonate also used as decorative and dimension stone. It is formed by rapid chemical precipitation around natural hot springs. A similar material is precipitated from cold water solutions as stalagmites and stalactites.
This is known as onyx marble (true onyx is banded quartz), Mexican onyx,
Algerian onyx, and oriental alabaster (true alabaster is dense gypsum).
Aragonite sand comprises extensive marine deposits off the south Florida coast. It is recovered by suction dredging and after drying and screening grades about 96% calcium carbonate. Most is used locally in cement manufacture.
The important uses of Calcium carbonate are:
- Sand-lime brick
- Paper
- Sugar
- Leather
- Calcium carbide
- Bleaching powder
- Textile
- Water and sewage treatment
- Soil reclamation
- Soil and asphalt stabilization
- Sealant
- Mineral wool
- Cements
- high-alumina cement , white cement and pozzolanic cement)
- Iron
- Steel
- Glass
- Nitro-lime fertilizer
- Sodium chemical
- Glazing of ceramic bodies
- Rubber