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Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO 3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed ...
Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula Mg 3 Si 4 O 10 (OH) 2.Talc in powdered form, often combined with corn starch, is used as baby powder.
Calcite alabaster, harder than the gypsum variety, was used in ancient Egypt and the wider Middle East (except Assyrian palace reliefs), and also in modern times. It is found as either a stalagmitic deposit from the floor and walls of limestone caverns , or as a kind of travertine , similarly deposited in springs of calcareous water.
The reason might be that calcite, dolomite form earlier at higher temperature (from mantle like fluids) which increases Mg/Ca ratio in the fluid sufficiently so as to precipitate magnesite. As this happens with increasing time, fluid cools, evolves by mixing with other fluids and when it forms magnesite, it decreases its temperature.
Limestone often contains larger crystals of calcite, ranging in size from 0.02 to 0.1 mm (0.79 to 3.94 mils), that are described as sparry calcite or sparite. Sparite is distinguished from micrite by a grain size of over 20 μm (0.79 mils) and because sparite stands out under a hand lens or in thin section as white or transparent crystals.
The definitions of the terms "steatite" and "soapstone" vary with the field of study. In geology, steatite is a rock that is, to a very large extent, composed of talc.
Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (Ca CO 3), the others being calcite and vaterite.It is formed by biological and physical processes, including precipitation from marine and freshwater environments.
The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO 3), and dolomite rock (also known as dolostone), which is composed of dolomite (CaMg(CO 3) 2). They are usually classified on the basis of texture and grain size. [1] Importantly, carbonate rocks can exist as metamorphic and igneous ...