Dolomite is a common mineral and an important carbonate rock. It can be used as both a mineral and a rock name.
Basic Overview
Chemical Composition: CaMg(CO₃)₂, i.e., calcium magnesium carbonate. It often contains elements such as iron and manganese, which can substitute for magnesium to form varieties such as iron dolomite and manganese dolomite.
Crystal Structure: Trigonal crystal system. Crystals are usually rhombohedral, and the crystal faces are often curved into a saddle shape, which is a very unique identifying feature.
Physical Properties:
Color: Usually white or grayish-white, but can also appear pink, yellow, or brown due to impurities.
Luster: Vitreous to pearly luster.
Hardness: 3.5 - 4 (Mohs hardness), harder than a fingernail, but easily scratched by a knife.
Cleavage: Has three sets of perfect cleavage (rhombohedral cleavage).
Distinguishing Dolomite from Calcite: Dolomite is easily confused with calcite (CaCO₃) in appearance. The most reliable method of identification is using cold, dilute hydrochloric acid:
Calcite: Effervesces vigorously in cold, dilute hydrochloric acid.
Dolomite: Powdered dolomite reacts with cold, dilute hydrochloric acid, but lumpy dolomite effervesces very weakly or not at all in cold, dilute hydrochloric acid. It only reacts vigorously in heated hydrochloric acid.
