Mineral · Calcite group
Calcite
CaCO3
Calcite is calcium carbonate, the most varied mineral in crystal habit and the second most common in collections: rhombohedra, scalenohedra (dogtooth), nailheads, twins and optical Iceland spar, in every colour. Classic sources are Elmwood (Tennessee), Cumbria, Mexico, China and the Tri-State district. It effervesces in dilute hydrochloric acid, has perfect rhombohedral cleavage and hardness 3, which distinguishes it from quartz and aragonite.
| Formula | CaCO3 |
|---|---|
| IMA status | grandfathered |
| Crystal system | Trigonal |
| Mohs hardness | 3 |
| Group | Calcite group |
| Type locality | None (known since antiquity) |
| Streak | White |
| Specific gravity | 2.71 |
| Reference list | IMA List of Minerals (RRUFF) — verify formula and status against the current list |
Fakes and treatments
Some 'calcite' from China is dyed or coated; honey-coloured Elmwood calcites are sometimes artificially cleaned of overgrowths. Cobaltoan calcite is often relabelled as the rarer sphaerocobaltite.
Elsewhere
Cite this article
Stratum Strata. "Calcite" (Mineral). Stratum Strata pack 2026.09, as of 2026-09-21. https://stratum.black/strata/minerals/calcite. Accessed 2026-09-21.
@misc{stratum-calcite,
title = {Calcite},
author = {{Stratum Strata}},
howpublished = {\url{https://stratum.black/strata/minerals/calcite}},
year = {2026},
note = {Mineral article, Stratum Strata pack 2026.09, as of 2026-09-21; sources: stratum, wikidata, commons. Accessed 2026-09-21.}
} Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.