A mineral containing calcium and magnesium carbonate, used primarily as an aggregate in making concrete. It is soft, often white, but may be transparent. Dolomite can be found on its own, but may also occur as a replacement mineral found in some rocks, particularly limestone, formed after action by magnesium-rich fluids. See also dolomitic limestone. RS Means Building Glossary (undated); English Heritage (2000). [J. Cassar, R. de Angelis]