LithoMap

Rock identification comparison

Limestone vs. dolostone: how to tell them apart

Limestone and dolostone are carbonate sedimentary rocks that can look nearly identical. Calcite-rich limestone normally fizzes vigorously with dilute acid on a fresh surface, while dolomite-rich dolostone usually reacts weakly unless powdered.

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Gray Salem Limestone hand specimen from Indiana
LimestoneCarbonate sedimentary rockPhoto: James St. John · CC BY-SA 4.0
Gray-brown Potosi Dolomite hand specimen, a Cambrian dolostone composed mainly of the mineral dolomite
DolostoneDolomite-rich sedimentary rockPhoto: Nessa Eull · CC0 1.0
Quick answer

The most useful distinction

Use a controlled acid response with texture and hardness. Immediate strong fizz favors limestone; weak surface reaction that strengthens on powder favors dolostone.

Side-by-side evidence

Limestone and Dolostone comparison table

PropertyLimestoneDolostoneHow to use it
Dominant mineralUsually calciteUsually dolomiteMineralogy produces the main field-test differences.
Dilute acid responseImmediate vigorous effervescence on a clean surfaceWeak or delayed on a surface; stronger when powderedThe most useful field distinction when performed safely.
HardnessNear Mohs 3 and scratched readily by steelNear Mohs 3.5 to 4 and slightly more resistantSupporting evidence when acid behavior is ambiguous.
Texture and fossilsMay preserve fossils, ooids, lime mud, or shellsOften crystalline or sugary, though fossils and sedimentary textures may surviveReplacement can erase or preserve original limestone features unevenly.
Field sequence

A practical identification sequence

  1. 1

    Expose a small fresh surface on expendable material.

  2. 2

    Observe texture, fossils, and crystal size before testing.

  3. 3

    Apply one small drop of dilute acid with eye protection.

  4. 4

    If reaction is weak, test a tiny powder only where lawful and appropriate.

Limits and cautions

Where the distinction gets difficult

  • Mixed calcite and dolomite can produce intermediate reactions.
  • Weathered rinds and coatings suppress effervescence.
  • Never acid-test monuments, finished stone, fossils, or protected outcrops.

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

Common questions

Limestone vs. dolostone FAQ

Is dolostone the same as dolomite?

Dolomite is the mineral. Dolostone is a rock composed predominantly of that mineral, although older sources often call the rock dolomite.

Can dolostone contain fossils?

Yes. Dolomitization may preserve, blur, or destroy fossils depending on how replacement proceeded.

Does dolostone never fizz?

It can react weakly on a fresh surface and more clearly when powdered. Calcite impurities can cause localized strong fizz.

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.

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