RocksdayCalcite vs Milky Quartz
The quickest way to tell Calcite from Milky Quartz: Milky Quartz scratches glass (Mohs 7); Calcite can't (Mohs 3).
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
The common white quartz. The cloudiness is light scattering off microscopic fluid bubbles trapped as the crystal grew.
Photo: James St. John, CC BY 2.0
Quick tests
- Scratch glass: Milky Quartz scratches glass (Mohs 7); Calcite can't (Mohs 3).
- Acid (vinegar or dilute HCl): Calcite fizzes; Milky Quartz doesn't.
Key differences
- Calcite fizzes, cleaves into rhombs and is much softer.
Side by side
| Property | Calcite | Milky Quartz |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3 | 7 |
| Luster | Vitreous | Vitreous to greasy |
| Streak | White | White |
| Colors | Clear, White, Orange, Yellow, Blue, Green | White |
| Crystal system | Trigonal | Trigonal |
| Specific gravity | 2.71 | 2.65 |
| Formula | CaCO₃ | SiO₂ |
| Found in | Iceland; Chihuahua, Mexico | Arkansas; Minas Gerais, Brazil |
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 milky quartz
- White and translucent rather than glassy-clear.
- Hardness 7 — scratches glass, no cleavage.
- Often massive veins or chunky crystals.
Crystal system: Trigonal
Full Milky Quartz guide →More comparisons
Frequently asked questions
What is the difference between calcite and milky quartz?
Calcite is a mineral (CaCO₃) with a Mohs hardness of 3 and a vitreous luster, usually colorless, white, orange, yellow, blue or green. Milky Quartz is a mineral (SiO₂) with a Mohs hardness of 7 and a vitreous to greasy luster, usually white.
How can you tell calcite from milky quartz?
Milky Quartz scratches glass (Mohs 7); Calcite can't (Mohs 3). Calcite fizzes; Milky Quartz doesn't. Calcite fizzes, cleaves into rhombs and is much softer.
Could you tell them apart from a blurry close-up?
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