RocksdayApophyllite vs Calcite
How to tell them apart
A sparkling silicate from cavities in basalt, forming blocky square crystals with pyramid tips.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
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
Quick tests
- Hardness: Apophyllite is clearly harder: Mohs 4.5–5 versus 3.
- Acid (vinegar or dilute HCl): Calcite fizzes; Apophyllite doesn't.
Key differences
- Calcite fizzes and cleaves into rhombs.
Side by side
| Property | Apophyllite | Calcite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 4.5–5 | 3 |
| Luster | Vitreous to pearly | Vitreous |
| Streak | White | White |
| Colors | Clear, White, Green | Clear, White, Orange, Yellow, Blue, Green |
| Crystal system | Tetragonal | Trigonal |
| Specific gravity | 2.3–2.4 | 2.71 |
| Formula | KCa₄Si₈O₂₀(F,OH)·8H₂O | CaCO₃ |
| Found in | Pune, India; Nashik, India | Iceland; Chihuahua, Mexico |
Properties that are the same for both are grayed out.
How to identify apophyllite
- Clear or mint-green square prisms or pyramids.
- Pearly shine on the flat top faces.
- Softer than quartz — a knife scratches it.
Crystal system: Tetragonal
Full Apophyllite guide →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 →More comparisons
Could you tell them apart from a blurry close-up?
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