Limestone is a sedimentary rock. Limestone is a general term to denote calcareous stone, dolostone (dolomite rock) and marl. The most widespread variety of limestone is calcareous stone. Limestone is compsed largely of the mineral calcitewith the chemical designation calcium carbonate: CaCO3.
Dolostone differs from calcareous stone with its high percentage of the mineral dolomite (CaMg(CO3)2). Dolostone is mostly formed as a magnesium replacement of limestone or lime mud prior to lithification. Marl stands between calcareous stone and clay and it degrades easily due to the impact of weather.
Calcium carbonate can be found in nature in the form of different other varieties, e.g. chalk (lacustrine lime, spring chalk). The mineral calcite, that is usually very finely grained in limestone, may be sometimes found as beautiful transparent crystals with miraculous optical quality – birefringence.
In 1992 limestone was declared Estonia’s national rock.