Identification guide · Sedimentary Rocks
How to Identify Limestone
Limestone is usually white, gray, and tan with a dull luster and is opaque. 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 Oolite, Chalk, and Dolostone; the tests below separate them.
Limestone identification checklist
| Color | White, Gray, Tan, Yellow | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Dull | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Opaque | 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 | Variable by mineral grains | |
| 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. |
Extra tests for Limestone
Acid test. Fizzes in vinegar or dilute hydrochloric acid because of its carbonate content.
Limestone 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. Limestone vs Oolite →
Limestone is harder (Mohs 3) than Chalk (Mohs 1–2), so Limestone will scratch Chalk and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Limestone vs Chalk →
Both sit near Mohs 3, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Limestone vs Dolostone →
Limestone is harder (Mohs 3) than Diatomite (Mohs 1.5), so Limestone will scratch Diatomite and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Limestone vs Diatomite →
Field tips
- Check whether the specimen's color and texture match typical Limestone examples.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Limestone identification FAQ
How can you tell if a rock is Limestone?
Check the color (white, gray, tan, and yellow), the dull 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 Limestone?
Limestone has a Mohs hardness of 3. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
What is the difference between Limestone and Oolite?
Limestone (Mohs 3, dull luster) and Oolite (Mohs 3, dull luster) look alike, but hardness, streak and heft usually separate them. See the full Limestone vs Oolite comparison for a side-by-side table.
Is Limestone worth anything?
Entry-level Limestone specimens sell for around $1, typical collector pieces about $10, and premium examples $50 or more depending on size, quality and locality.
What color is Limestone?
Limestone is most often white, gray, tan, and yellow. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
