Dolomite from Vekol mine, Pinal Co., Arizona, USA
Credit: Weinrich Minerals, Inc


Very lustrous chocolate brown rhombohedral crystals of dolomite the front of this matrix. This is iron rich giving at the color that it is. In very good condition.

Dolomite is a calcium/magnesium carbonate mineral. Dolomite was first described in 1791 as a rock by Deodat de Dolomieu, who investigated samples from the Italian Alps.

Dolomite has a trigonal crystal system with rhombohedral habit. In ideal dolomite, calcium and magnesium are separated into completed separate planes, quite unlike magnesian calcites in which Mg randomly substitutes for Ca. Most dolomite samples contain only a few percent of substitution of calcium for magnesium, and vice versa.

It forms white, tan, gray, or pink crystals. Dolomite is a double carbonate, having an alternating structural arrangement of calcium and magnesium ions. Unless it is in fine powder form, it does not rapidly dissolve or effervesce (fizz) in cold dilute hydrochloric acid as calcite does. Crystal twinning is common. 

Formula: CaMg(CO3)2
Crystal system:    Trigona
Tenacity:    Brittle
Mohs scale hardness:  3.5 to 4