LithoMap

Mineral identification comparison

Gypsum vs. calcite: how to tell them apart

Gypsum and calcite are common pale minerals in sedimentary rocks, veins, and caves. Gypsum is much softer and can be scratched by a fingernail; calcite resists a fingernail but reacts strongly with dilute acid.

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Gypsum mineral specimen with clear bladed crystals
GypsumSulfate mineral · CaSO₄·2H₂OPhoto: Robert M. Lavinsky · CC BY-SA 3.0
Calcite mineral specimen with pale translucent crystals
CalciteCarbonate mineral · CaCO₃Photo: Raimond Spekking · CC BY-SA 4.0
Quick answer

The most useful distinction

Begin with hardness. A fingernail scratch favors gypsum; material that resists a fingernail but scratches under a copper coin favors calcite. A clean calcite surface then fizzes readily with dilute acid.

Side-by-side evidence

Gypsum and Calcite comparison table

PropertyGypsumCalciteHow to use it
HardnessMohs 2; scratched easily by a fingernailMohs 3; resists a fingernail but is scratched by copper or steelThe fingernail test is the simplest nonchemical separation on a fresh surface.
Acid responseNo ordinary effervescence with dilute hydrochloric acidReadily effervesces on a clean surfaceAcid confirms calcite after hardness narrows the choice.
Cleavage and habitOne perfect cleavage with other directions less distinct; tabular, fibrous, bladed, or massive formsThree perfect directions not at 90°, commonly yielding rhombohedral fragmentsHabit and cleavage help when scratches are ambiguous.
Feel and flexibilitySome clear sheets are slightly flexible but not elastic; fibrous forms may feel silkyCleavage fragments are brittle and do not form flexible sheetsThis is supporting evidence and varies with form.
Field sequence

A practical identification sequence

  1. 1

    Try a fingernail on a clean, inconspicuous edge.

  2. 2

    Inspect broken surfaces for rhombohedral calcite cleavage or tabular and fibrous gypsum habits.

  3. 3

    Use dilute acid safely on an expendable fresh spot if calcite remains possible.

  4. 4

    Confirm that coatings, clay, or mixed grains are not controlling the test.

Limits and cautions

Where the distinction gets difficult

  • Fine-grained evaporite rock can mix gypsum, carbonate, clay, and salts.
  • A weathered or polished surface may give an unreliable scratch.
  • Never taste an unknown mineral or apply acid to caves, formations, finished stone, or valuable material.

Use several independent observations. This comparison supports preliminary field identification, not laboratory confirmation, appraisal, proof of origin, or collecting permission.

Common questions

Gypsum vs. calcite FAQ

Can gypsum fizz in acid?

Gypsum does not produce the strong carbonate effervescence expected from calcite. Fizzing may come from admixed calcite or a carbonate coating.

Can calcite be scratched by a fingernail?

Typical calcite is slightly harder than a fingernail. Powdery weathering, thin edges, or soft material on the surface can create a misleading result.

Are transparent gypsum and calcite easy to confuse?

They can look alike, but hardness, cleavage geometry, and acid response separate fresh specimens reliably in most field situations.

Source basis

Authoritative sources

LithoMap wrote this comparison in original language from the physical properties and geological concepts supported by these public scientific references.

Editorial review: September 17, 2026.

Resolve another lookalike

More mineral comparisons

All mineral guides
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