Identification guide · Minerals
How to Identify Calcite
Calcite is usually colorless, white, and yellow with a vitreous luster and is transparent. It has a Mohs hardness of 3. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Its streak is white. It is most often confused with Aragonite, Gypsum, and Fluorite; the tests below separate them.
Calcite identification checklist
| Color | Colorless, White, Yellow, Orange, Blue, Green, Pink | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Transparent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 3 | A copper coin (Mohs 3.5) scratches it, but a fingernail does not. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect rhombohedral | |
| Fracture | Conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.7 | Ordinary rock-like heft (specific gravity about 2.7), similar to quartz. |
| Crystal system | Trigonal |
Extra tests for Calcite
Acid test. Fizzes in vinegar or dilute hydrochloric acid because of its carbonate content.
Glass check. Calcite shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Calcite look-alikes and how to tell them apart
Both sit near Mohs 3, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Calcite vs Aragonite →
Calcite is harder (Mohs 3) than Gypsum (Mohs 2), so Calcite will scratch Gypsum and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Calcite vs Gypsum →
Fluorite is harder (Mohs 4) than Calcite (Mohs 3), so Fluorite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Calcite vs Fluorite →
Both sit near Mohs 3, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Calcite vs Anhydrite →
Field tips
- Check whether the specimen's color and texture match typical Calcite examples.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Calcite identification FAQ
How can you tell if a rock is Calcite?
Check the color (colorless, white, yellow, and orange), the vitreous luster, a Mohs hardness of 3 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Calcite?
Calcite has a Mohs hardness of 3. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
What is the difference between Calcite and Aragonite?
Calcite (Mohs 3, vitreous luster) and Aragonite (Mohs 3.5–4, vitreous to resinous luster) look alike, but hardness, streak and heft usually separate them. See the full Calcite vs Aragonite comparison for a side-by-side table.
Is Calcite worth anything?
Entry-level Calcite specimens sell for around $2, typical collector pieces about $15, and premium examples $100 or more depending on size, quality and locality.
What color is Calcite?
Calcite is most often colorless, white, yellow, and orange. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
