Kalsitt

Kalsitt, or calcite, is a widely distributed carbonate mineral with the chemical formula CaCO3. It is the most stable polymorph of calcium carbonate at Earth's surface and occurs in a diverse range of geological environments. Calcite forms in sedimentary rocks such as limestone and marble, in hydrothermal veins, and as precipitates in caves where it creates stalactites and stalagmites. It also appears as large transparent crystals in geodes and some metamorphic rocks.

Crystal structure and properties: Calcite crystallizes in the trigonal crystal system and commonly forms rhombohedra and scalenohedra. It has perfect cleavage in three directions parallel to rhombohedral planes, producing easily recognizable rhombohedral fragments. Its hardness on the Mohs scale is 3, and the specific gravity is about 2.71. The color is typically white or colorless, but impurities can give a broad range of colors and patterns. Calcite is strongly birefringent (double refraction) and exhibits a pronounced optical effect under polarized light.

Identification: Calcite effervesces in dilute hydrochloric acid due to the release of carbon dioxide, a classic diagnostic test.

Uses and significance: Calcite is the primary source of industrial lime and cement and is widely used as a building stone and chemical feedstock. Crystals of calcite, especially Iceland spar, are valued for optical applications because of their transparency and strong birefringence.

Names and varieties: The term kalsitt is used in several languages for calcite. Common varieties include Iceland spar, dogtooth spar, and various twinned crystal forms.