mineralscalcite

Calcite is a widely distributed carbonate mineral with the chemical formula CaCO3. It is one of the two common polymorphs of calcium carbonate, the other being aragonite. Calcite crystallizes in the trigonal crystal system and occurs in a wide range of habits, from well-formed rhombohedra to massive beds. It is typically colorless or white but can show yellow, orange, red, green, blue, or brown hues due to impurities. Calcite has a Mohs hardness of 3 and a specific gravity of about 2.71. It exhibits perfect rhombohedral cleavage and notable birefringence when viewed in polarized light.

In nature, calcite forms in many environments. It is a major component of sedimentary rocks such as limestone and chalk, and it can precipitate from groundwater to create cave features known as speleothems. It also occurs as a cementing material in clastic rocks and as a biological carbonate material in shells and coral skeletons. The mineral readily effervesces in dilute hydrochloric acid.

Calcite has a number of industrial and decorative uses. It is an important source of lime and cement and serves as a filler in various products. It is used to adjust soil pH in agriculture and, in a decorative context, as a gem or ornamental stone in various colors. A notable variety is Iceland spar, a transparent form with strong double refraction used in optical applications.

The name calcite derives from the Latin calx, calis, meaning limestone.