RocksdayCalcite vs Dolomite
How to tell them apart
One of the most common minerals on Earth and the main ingredient of limestone and marble. It breaks into perfect slanted boxes (rhombs) and fizzes in acid.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
A calcium magnesium carbonate that forms whole mountain ranges of dolostone and pearly, curved 'saddle' crystals.
Photo: Didier Descouens, CC BY-SA 4.0
Quick tests
- Acid (vinegar or dilute HCl): Calcite fizzes; Dolomite doesn't.
Key differences
- Dolomite barely fizzes unless powdered first.
- Calcite fizzes vigorously and is a bit softer.
Side by side
| Property | Calcite | Dolomite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3 | 3.5–4 |
| Luster | Vitreous | Vitreous to pearly |
| Streak | White | White |
| Colors | Clear, White, Orange, Yellow, Blue, Green | White, Pink, Gray |
| Crystal system | Trigonal | Trigonal |
| Specific gravity | 2.71 | 2.84–2.86 |
| Formula | CaCO₃ | CaMg(CO₃)₂ |
| Found in | Iceland; Chihuahua, Mexico | Eugui, Spain; The Dolomites, Italy |
Properties that are the same for both are grayed out.
How to identify calcite
- Fizzes in cold dilute hydrochloric acid (or slowly in vinegar).
- Breaks into rhomb-shaped pieces along three cleavage planes.
- Hardness 3 — a copper coin barely scratches it, a knife easily does.
- Clear pieces show double images of text underneath.
Crystal system: Trigonal
Full Calcite guide →How to identify dolomite
- Curved, saddle-shaped rhomb crystals.
- Fizzes only weakly — or only when scratched into powder.
- Pearly luster.
- A bit harder than calcite.
Crystal system: Trigonal
Full Dolomite guide →More comparisons
Could you tell them apart from a blurry close-up?
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