Rock and Mineral Identification Reference

How to Identify Gypsum: Hardness, Streak, Luster and Tests

Quick answer

Gypsum (mineral): 6 identifying properties, 1 home test, and how to tell it from Halite, quoted from geology department and survey sources.

Updated 2026-09-10 · Sources: University of Minnesota Common Minerals

Scratch, streak and acid tests mark the specimen, and some produce sharp fragments or dust. Wear eye protection, work in a ventilated space, keep acid off skin, and never taste a mineral you have not already identified.

How to Identify Gypsum: Hardness, Streak, Luster and Tests — Photo: Robert M. Lavinsky · CC BY-SA 3.0 · source

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What are the key facts?

Type: Mineral
Mohs hardness: 2 (very soft)
Streak: White
Luster: Vitreous to pearly luster in crystals; massive form is dull.
Color: Usually white, colorless, or gray; impurities can produce red, brown, or yellow tones.
Cleavage or fracture: One direction of perfect cleavage and two fair directions, producing thin rhombic fragments.
Specific gravity: 2.3

What Gypsum looks like

The properties that identify Gypsum — mohs hardness: 2 (very soft); streak: White; luster: Vitreous to pearly luster in crystals; massive form is dull; color: Usually white, colorless, or gray; impurities can produce red, brown, or yellow tones; cleavage or fracture: One direction of perfect cleavage and two fair directions, producing thin rhombic fragments; specific gravity: 2.3. Hardness, streak and cleavage are the reliable ones; color alone rarely settles it.

Tests you can do at home

Hardness of 2 — can be scratched with a fingernail; does not react with dilute HCl (distinguishing it from calcite).

Often confused with

[Halite](/lookup/rocks-and-minerals/halite): A taste test distinguishes them: halite tastes salty, gypsum does not.

Where it is found in North America

Gypsum crystals occur in old Wisconsin mine workings, and selenite gypsum crystals occur in Cretaceous-age clays in central and western Minnesota.

How to photograph it for identification

Photograph a fresh, unweathered surface in daylight, then a second shot of any crystal faces or broken edge. Include a coin for scale. If you did a streak test, photograph the streak next to the specimen. The app suggests the likely mineral or rock; confirm with hardness and the tests above before you label it.

FAQ

How hard is Gypsum on the Mohs scale?

2 (very soft). A fingernail is about 2.5, a copper coin about 3, a steel knife 5.5 and glass about 5.5, so test against those.

What color streak does Gypsum leave?

White. Rub the specimen on an unglazed porcelain tile; the powder color is the streak, and it is more consistent than the specimen color.

How do I tell Gypsum from Halite?

A taste test distinguishes them: halite tastes salty, gypsum does not.

What is the simplest test for Gypsum?

Hardness of 2 — can be scratched with a fingernail; does not react with dilute HCl (distinguishing it from calcite).

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Sources

University of Minnesota Common Mineralscommonminerals.esci.umn.edu/minerals-g-m/gypsum
University of Minnesota Common Mineralscommonminerals.esci.umn.edu/minerals-g-m/halite

Compiled by the RockLens editorial team

Every fact on this page is taken from the sources listed above; numbers and prices are copied from the source, and prices name the guide or auction and its date. Research and drafting were assisted by AI, and each claim was then checked against the cited sources. Checked 2026-09-10. We do not buy, sell or grade items; the app identifies what you photograph and points you to these references.