The mineral calcite (also known as calcite) consists mainly of the salt is calcium carbonate (CaCO3), and is one of the most common mineral in the earth's crust. Calcium carbonate is caused by soluble calcium ions come in contact with CO2 (carbon dioxide forms a carbonate ion as a positive ion is in a solution). Calcium carbonate is a poorly soluble salt, which makes the formed CaCO3 precipitates; this is going according to the following reaction: Ca2 + (aq) + CO32- (aq) - → CaCO3 (s) Calcite is a general constituent of sedimentary rocks, and in veins of deposits in hot springs and cave in karst regions (as stalactite). It is the mineral which forms of limestone and therefore the most common mineral of biological origin. Calcite is the main component of limestone, chalk and marble and is a major constituent of limestone, calcareous sandstone and limestone shale. Calcite gives the chemical weathering in igneous and metamorphic rocks, creating sedimentary rocks occur. Calcite is under slight pressure soluble in CO2-containing water. During the fall in the air, the gaseous carbon dioxide takes rainwater on, making it acidic. This acidic rainwater is able to dissolve lime. In underground streams can convey this material in solution to, upon contact with atmospheric pressure, CO2 escapes and the calcite precipitate. As stalagmites and stalactites are formed in caves. Previously, the transparent Icelandic form of calcite, which was named Iceland spar, used for the manufacture of Nicol prisms. Some researchers hypothesize that the Vikings at sea navigated using crystals of this mineral, which even in cloudy weather to determine the sun's position is accurate. Nowadays, especially in the construction of limestone used as a construction element, for the manufacture of lime and cement, while marble is used as a construction -en ornamental stone.