kalsiitti

Kalsiitti, or calcite in English, is a common carbonate mineral with the chemical formula CaCO3. It is one of the most widespread minerals in sedimentary rocks and is the principal constituent of limestone and marble. Calcite occurs in a wide range of colors due to impurities, but is often white or colorless in its pure form. It crystallizes in the trigonal (rhombohedral) system and commonly forms rhombohedral crystals; it exhibits perfect rhombohedral cleavage in three directions. The Mohs hardness is about 3, and the specific gravity is around 2.71. A notable property is its strong birefringence, which can cause double refraction in transparent specimens. Calcite effervesces vigorously with cold, dilute hydrochloric acid, releasing carbon dioxide.

Calcite is one of the two common polymorphs of calcium carbonate, the other being aragonite, with calcite being the more stable form at Earth's surface conditions. It forms in sedimentary environments from precipitation of CaCO3, in shells and skeletal structures of marine organisms, and in caves as stalactites, stalagmites, and other speleothems. It also occurs in metamorphic rocks such as marble, where limestone has been recrystallized, and in hydrothermal veins.

Uses of calcite are diverse. It is a major source of lime and cement and serves as a filler in paints, plastics, and paper. It is also used as a decorative stone. Varieties include Iceland spar, a highly transparent calcite with pronounced birefringence, and dogtooth calcite, known for stepped crystal faces.

Etymology: the name derives from Latin calx, meaning lime or stone.