sedimentary

Dolomite (Dolostone)

Dolomite [CaMg(CO3)2]

Hardness: 3.5-4; Color: Gray, tan, or buff; Luster: Pearly to sub-vitreous; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral; Grainy texture.

Hardness: 3
Color: Gray, tan, or buff
Luster: Pearly to sub-vitreous

Identified June 26, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3.5-4; Color: Gray, tan, or buff; Luster: Pearly to sub-vitreous; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral; Grainy texture.

Formation & geological history

Formed by the chemical modification of magnesium-rich groundwater acting on lime mud and limestone (dolomitization). Common in the Paleozoic bedrock of the Upper Midwest/driftless area.

Uses & applications

Used as a source of magnesium, in the production of concrete and asphalt, for soil pH correction in agriculture, and as crushed stone for building foundations.

Geological facts

This specimen was found in the 'Driftless Area' of Iowa/Illinois/Wisconsin, a region famous for its unglaciated Paleozoic dolomite bluffs. Dolostone is often more resistant to weathering than limestone, leading to prominent cliff formations.

Field identification & locations

Identify by its reaction to cold dilute hydrochloric acid: it only fizzes when powdered or scratched, unlike limestone which fizzes immediately. Look for rhombohedral crystals in cavities within the rock.