RocksdayCalcite vs Magnesite
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
Magnesium carbonate, usually as white porcelain-like masses with a cauliflower texture.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Acid (vinegar or dilute HCl): Calcite fizzes; Magnesite doesn't.
Key differences
- Calcite fizzes readily in cold acid.
Side by side
| Property | Calcite | Magnesite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3 | 3.5–4.5 |
| Luster | Vitreous | Vitreous to dull |
| Streak | White | White |
| Colors | Clear, White, Orange, Yellow, Blue, Green | White, Gray, Yellow |
| Crystal system | Trigonal | Trigonal |
| Specific gravity | 2.71 | 3 |
| Formula | CaCO₃ | MgCO₃ |
| Found in | Iceland; Chihuahua, Mexico | Liaoning, China; Austria |
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 magnesite
- Chalky to porcelain-white, often knobbly.
- Fizzes only in warm acid or as powder.
- Harder than calcite.
Crystal system: Trigonal
Full Magnesite guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday