# How to identify dolomite

Canonical page: https://lithomap.app/resources/mineral-identification/dolomite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap mineral identification reference for field observations, search systems, and language models.
Classification: Carbonate mineral · CaMg(CO₃)₂

## Summary

Dolomite is a calcium-magnesium carbonate with rhombohedral cleavage and hardness about 3.5 to 4; unlike calcite, an unpowdered fresh surface usually reacts weakly with cold dilute acid.

## Quick identification clues

- Mohs hardness about 3.5 to 4
- Three rhombohedral cleavage directions
- White, gray, tan, pink, or brown
- Weak acid response on a fresh unpowdered surface; stronger when powdered

## Composition and classification

Dolomite contains calcium, magnesium, carbonate, and commonly minor iron or manganese. “Dolomite” names the mineral; “dolostone” is the preferred name for a sedimentary rock composed largely of dolomite.

## Appearance

Crystals are commonly rhombohedral and may have curved or saddle-shaped faces. Massive dolomite can be fine grained, sugary, porous, or difficult to distinguish visually from limestone.

Iron-bearing material weathers tan to brown. Pink hues may reflect manganese, while coatings and mixed calcite can change the apparent reaction and color.

## Identification tests

- Hardness: 3.5 to 4. Harder than calcite and not scratched easily by copper.
- Streak: White. Consistent but not diagnostic.
- Cleavage: Perfect in three directions not at 90°. Produces rhombohedral fragments similar to calcite.
- Acid response: Weak on a cold fresh surface; stronger when powdered. A controlled powdered test helps separate dolomite from readily effervescent calcite.

## Common lookalikes

- Calcite: Softer and reacts vigorously with dilute acid on a clean unpowdered surface.
- Magnesite: Similar carbonate with different composition; laboratory confirmation may be needed in fine-grained material.
- Dolostone: A rock made mostly of dolomite rather than an individual mineral crystal.

## Direct side-by-side comparisons

- Calcite vs. dolomite — https://lithomap.app/resources/mineral-identification/compare/calcite-vs-dolomite

## Most relevant related guides

- Calcite — https://lithomap.app/resources/mineral-identification/calcite
- Apatite — https://lithomap.app/resources/mineral-identification/apatite
- Augite — https://lithomap.app/resources/mineral-identification/augite
- Azurite — https://lithomap.app/resources/mineral-identification/azurite

## Formation

Much sedimentary dolomite forms when magnesium-rich fluids alter earlier carbonate sediment or limestone during burial or fluid circulation.

Dolomite also forms in hydrothermal veins, metamorphic marble, evaporative settings, and some modern saline environments. Its origin can remain complex even where the mineral is easy to confirm.

## Occurrence and geologic setting

Dolomite is widespread in carbonate sedimentary successions, hydrothermal veins, altered limestones, and metamorphic rocks. It may host groundwater, petroleum, and Mississippi Valley–type mineralization.

Acid response varies with grain size, temperature, coatings, porosity, and calcite impurities, so one ambiguous test should not carry the identification.

## Uses and significance

Dolomite and dolostone are used as aggregate, dimension stone, soil amendment, refractory feedstock, and sources of magnesium-bearing material.

## Field safety and limitations

- Use acid only on an expendable chip and wear eye protection.
- Do not acid-test monuments, cave formations, fossils, or protected outcrops.
- Keep the mineral name dolomite distinct from the rock name dolostone in field notes.

## Authoritative sources

- Dolomite Deposit Near Marble, Stevens County, Washington — U.S. Geological Survey: https://pubs.usgs.gov/publication/b1027C
- 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

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/minerals/dolomite.webp
- Description: Pale dolomite crystals from Azcárate Quarry in Eugui, Navarre, Spain
- Creator: Didier Descouens
- License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/
- Source record: https://commons.wikimedia.org/wiki/File:Dolomite-Navarre.jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.