Dolomite

Dolomite is a calcium magnesium carbonate, CaMg(CO₃)₂, with trigonal crystals and a hardness of 3.5 to 4. Its crystals often have curved, saddle-shaped faces, and it is the main mineral of dolostone.

🪨 Geology Guide Specimen: Open Dolomite (Saddle Crystal) in the CRV Science Rock & Mineral ID Guide to log the specimen, compare it with the other 8 mineral classes of Dana / Strunz Classes, and test your eye in LithoClade.

In dolomite, layers of calcium and magnesium alternate between sheets of carbonate groups, an ordered arrangement that makes it a distinct mineral and not a mixture. It dissolves more slowly than calcite and reacts with cold dilute acid only when powdered.

Dolomite that grows from warm fluids in veins and cavities often forms pearly, pale pink or ivory crystals with curved faces, called saddle dolomite. The curvature arises from strain in the lattice as the crystal grows.

Dolomite makes dolostone and is common in hydrothermal veins and in the cavities of lead-zinc ores of the Mississippi Valley type. See magnesium, the element that sets it apart from calcite, and the Dolomites of Italy, named for the mineral.

• Dolostone — the rock made of dolomite
• Calcite — the related calcium carbonate
• Magnesium — the element that sets it apart