Identification

Calcite Identification Sheet

How to confirm calcite using hardness, cleavage, and the dilute-acid reaction test.

Rock type: Sedimentary, Hydrothermal

For: Collectors, Lapidary Artists

Mohs hardness 3
Streak White
Luster Vitreous, Pearly Vitreous to pearly
CleavagePerfect rhombohedral (three directions)
Crystal habit Rhombohedral, Scalenohedral, Massive Rhombohedral, scalenohedral, massive

Calcite is soft, has perfect rhombohedral cleavage, and reacts visibly with dilute acid. Those three traits separate it from quartz and most other clear-to-white minerals.

Common lookalikes

Quartz (harder, no cleavage, no acid reaction), dolomite (reacts only when powdered), aragonite (different crystal habit).