RocksdayCalcite vs Celestine
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
Strontium sulfate, best known for pale sky-blue crystals filling geodes from Madagascar.
Photo: Ivar Leidus, CC BY-SA 4.0
Quick tests
- Acid (vinegar or dilute HCl): Calcite fizzes; Celestine doesn't.
- Heft: Celestine feels noticeably heavier for its size (specific gravity 3.95–3.97 vs 2.71).
Key differences
- Blue calcite fizzes in acid.
Side by side
| Property | Calcite | Celestine |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3 | 3–3.5 |
| Luster | Vitreous | Vitreous to pearly |
| Streak | White | White |
| Colors | Clear, White, Orange, Yellow, Blue, Green | Blue, White, Clear |
| Crystal system | Trigonal | Orthorhombic |
| Specific gravity | 2.71 | 3.95–3.97 |
| Formula | CaCO₃ | SrSO₄ |
| Found in | Iceland; Chihuahua, Mexico | Sakoany, Madagascar; Put-in-Bay, Ohio |
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 celestine
- Pale sky blue, sometimes white.
- Bladed or tabular crystals.
- Heavy for a pale mineral.
- Turns a flame crimson red.
Crystal system: Orthorhombic
Full Celestine guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday