Mangano Calcite in very nice presentation box from Bulgaria.

The mineral calcite (also called calcite) consists mainly of the salt calcium carbonate (CaCO3) and is one of the most abundant minerals in the earth's crust. Calcium carbonate is formed when soluble calcium ions come into contact with CO2 (carbon dioxide forms a carbonate ion when there is a positive ion in a solution). Calcium carbonate is a sparingly soluble salt, causing the CaCO3 formed to precipitate; this goes according to the following reaction: Ca2 + (aq) + CO32- (aq) - → CaCO3 (s) Calcite is a common constituent of sedimentary rocks, veins and in deposits in hot springs and caverns in karst areas (as dripstone). It is the mineral that forms limestone and is therefore the most abundant mineral of biological origin. Calcite is the main constituent of limestone, chalk rock and marble and it is also an important constituent of marl, calcareous sandstone and limestone shales. Calcite provides chemical weathering in igneous and metamorphic rocks, resulting in sedimentary rocks. Calcite is soluble in CO2-containing water under light pressure. As it falls into the air, rainwater absorbs the gaseous carbon dioxide, making it acidic. This acidic rainwater is able to dissolve lime. In underground currents this material can transport in solution until, after contact with atmospheric pressure, CO2 escapes and the calcite precipitates. This is how stalagmites and stalactites are formed in caves. In the past, the transparent Icelandic form of calcite, called Icelandspar, was used to make Nicolprisms. Some researchers assume that the Vikings navigated the sea with the help of crystals of this mineral, with which the position of the sun can be accurately determined even in cloudy weather. Nowadays limestone is mainly used in construction as a building element, for the manufacture of lime and cement, while marble is used as construction and ornamental stone.