Identification guide · Sedimentary Rocks
How to Identify Dolomite
Dolostone is typically pale gray, cream, tan, or pinkish, with a dull to slightly pearly luster on cleavage faces and a white streak. Its hardness of about 3.5 to 4 is close to calcite, but the classic field test is its reaction to acid, dolostone fizzes only weakly or not at all with cold dilute hydrochloric acid unless powdered, whereas limestone bubbles vigorously. Weathered dolostone surfaces often develop a rough, sugary, or pitted texture, and individual dolomite crystals within the rock may show a curved, saddle-shaped habit rarely seen in calcite.
Dolomite identification checklist
| Color | White, Gray, Pink, Brown, Yellow | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous to dull | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 3.5–4 | A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Fracture | Conchoidal to uneven | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.8–2.9 | Ordinary rock-like heft (specific gravity about 2.8499999999999996), similar to quartz. |
Extra tests for Dolomite
Glass check. Dolomite 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.
Dolomite look-alikes and how to tell them apart
Both sit near Mohs 3.5–4, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Dolomite vs Calcite →
Quartz is harder (Mohs 7) than Dolomite (Mohs 3.5–4), so Quartz will scratch Dolomite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Dolomite vs Quartz →
Conglomerate is harder (Mohs 3–7) than Dolomite (Mohs 3.5–4), so Conglomerate will scratch Dolomite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Dolomite vs Conglomerate →
Both sit near Mohs 3.5–4, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Dolomite identification FAQ
How can you tell if a rock is Dolomite?
Check the color (white, gray, pink, and brown), the vitreous to dull luster, a Mohs hardness of 3.5–4 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Dolomite?
Dolomite has a Mohs hardness of 3.5–4. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
What is the difference between Dolomite and Calcite?
Dolomite (Mohs 3.5–4, vitreous to dull luster) and Calcite (Mohs 3, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Dolomite vs Calcite comparison for a side-by-side table.
Is Dolomite worth anything?
Entry-level Dolomite specimens sell for around $1, typical collector pieces about $10, and premium examples $75 or more depending on size, quality and locality.
What color is Dolomite?
Dolomite is most often white, gray, pink, and brown. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
