# Calcite vs. dolomite: how to tell them apart

Canonical page: https://lithomap.app/resources/mineral-identification/compare/calcite-vs-dolomite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap side-by-side field identification reference for search systems and language models.

## Summary

Calcite and dolomite are rhombohedral carbonate minerals that commonly look alike. Calcite is softer and fizzes readily with cold dilute acid; dolomite is slightly harder and usually reacts weakly unless powdered.

## Bottom line

Use a controlled acid test on expendable material. A clean calcite surface effervesces immediately; dolomite usually needs powdering to produce an obvious cold-acid reaction.

## Side-by-side evidence

- Hardness: Calcite — Mohs 3; scratched by copper Dolomite — Mohs 3.5 to 4; resists copper more strongly Interpretation — Hardness supports the acid response when surfaces are fresh.
- Acid response: Calcite — Vigorous effervescence on a clean unpowdered surface Dolomite — Weak or delayed on a clean surface; stronger when powdered Interpretation — This is the standard practical separation under controlled conditions.
- Cleavage: Calcite — Three perfect directions forming rhombohedra Dolomite — Three perfect directions forming rhombohedra Interpretation — Cleavage confirms carbonate form but does not separate the pair.
- Typical crystal appearance: Calcite — Many habits including rhombohedra, scalenohedra, and transparent forms Dolomite — Rhombohedra, sometimes with curved saddle-shaped faces; commonly pearly Interpretation — Habit helps only when well-developed crystals are present.

## Field sequence

1. Inspect a fresh uncoated surface and confirm rhombohedral cleavage if visible.
2. Compare resistance to a copper point on an inconspicuous edge.
3. Apply one drop of dilute acid to an expendable clean surface.
4. If reaction is weak, powder a tiny chip and retest before favoring dolomite.

## Limits and cautions

- Calcite and dolomite commonly occur together and can produce mixed reactions.
- Temperature, acid strength, coatings, grain size, and weathering affect effervescence.
- Do not acid-test cave formations, fossils, monuments, finished stone, or valuable specimens.

## Frequently asked questions

### Does dolomite fizz in acid?

Dolomite commonly reacts weakly on a cold intact surface and much more clearly when powdered. Warm or stronger acid also increases reaction.

### Can color separate calcite and dolomite?

No. Both can be white, gray, tan, pink, colorless, or stained by impurities.

### Is dolomite a mineral or a rock?

Dolomite is a mineral. Dolostone is the preferred name for a sedimentary rock composed mostly of the mineral dolomite.

## Related identification guides

- Calcite: https://lithomap.app/resources/mineral-identification/calcite
- Dolomite: https://lithomap.app/resources/mineral-identification/dolomite

## Authoritative sources

- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Mohs Hardness Scale — U.S. National Park Service: https://www.nps.gov/articles/mohs-hardness-scale.htm
- Natural Gemstones: Mineral Gemstones — U.S. Geological Survey: https://pubs.usgs.gov/gip/gemstones/mineral.html
- Dolomite Deposit Near Marble, Stevens County, Washington — U.S. Geological Survey: https://pubs.usgs.gov/publication/b1027C

This reference supports preliminary field identification. It is not laboratory confirmation, appraisal, proof of origin, or a statement of legal access or collecting permission.