|TALC, STEATITE AND SOAPSTONE|
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. In loose form, it is the widely used substance known as talcum powder. It occurs as foliated to fibrous masses, its monoclinic crystals being so rare as to be almost unknown. It has a perfect basal cleavage, and the folia are non-elastic, although slightly flexible. It is sectile and very soft, with a hardness of 1 (Talc is the softest of the Mohs’ scale of mineral hardness, and can be easily scratched by a fingernail). It has a specific gravity of 2.5-2.8, a clear or dusty luster, and is translucent to opaque. Its colour ranges from white to grey or green and it has a distinctly greasy feel. Its streak is white.
Talc is a metamorphic mineral resulting from the metamorphism of magnesian minerals such as pyroxene, amphibole, olivine and other similar minerals in the presence of carbon dioxide and water. This is known as talc carbonation or steatization and produces a suite of rocks known as talc carbonates.
Talc is primarily formed via hydration and carbonation of serpentine, via the following reaction;
Serpentine + Carbon Dioxide → Talc + Magnesite + Water
Soapstone (also known as steatite or soaprock) is a metamorphic rock, a talc-schist. It is largely composed of the mineral talc and is rich in magnesium. It is produced by dynamothermal metamorphism and metasomatism, which occurs at the areas where tectonic plates are subducted, changing rocks by heat and pressure, with influx of fluids, but without melting. It has been a medium for carving for thousands of years.
Petrologically, soapstone is composed dominantly of talc, with varying amounts of chlorite and amphiboles (typically tremolite, anthophyllite, and magnesiocummingtonite), and trace to minor FeCr-oxides. It may be schistose or massive. Soapstone is formed by the metamorphism of ultramafic protoliths (e.g. dunite or serpentinite) and the metasomatism of siliceous dolostones.
Pyrophyllite, a mineral very similar to talc is sometimes called soapstone in the generic sense since its physical characteristics and industrial uses are similar, and because it is also commonly used as a carving material. However this mineral typically does not have such a soapy feel from which soapstone derives its name.
|TALC, STEATITE AND SOAPSTONE IN INDIA|
|The total all India resources are placed at 269.3 million tonnes as 1-4-2000. Out of these paper and textile grade forms 12.25%, cosmetics grade 28.13%, insecticide grade 14.40% and remaining 45.12% form unclassified ceramic, not known and other grades. Of the total 48.2% are in Reserves category, and 51.8% are Remaining Resources. Out of the total resources 21.6% are in the freehold and 78.4% in the leasehold areas. Major deposits of superior grade steatite are found in Bhilwara, Udaipur and Jaipur districts of Rajasthan, Jabalpur, and Jhabua districts of Madhya Pradesh and Durg district of Chhattisgarh. In Uttaranchal extensive deposits of massive soapstone occur in association with dolomites in Almora and Pithoragarh districts. All these deposits account for 80% of Resources. Remaining 15% is accounted mainly by Andhra Pradesh, Bihar, Maharashtra, Kerala and Orissa. The remaining 5% is shared by other states.|