Identification guide · Minerals
How to Identify Colemanite
Colemanite occurs as colorless to white, sometimes yellowish, glassy crystals or as compact nodular masses, showing a vitreous luster on fresh crystal faces. It has a white streak, a hardness of about 4 to 4.5, and distinct cleavage in one direction that produces bright, glassy cleavage flakes. Fracture on other surfaces is uneven to splintery. It is easily confused with other white borate or sulfate minerals like colorless gypsum, but colemanite's greater hardness and glassy crystal faces help distinguish it in hand specimen.
Colemanite identification checklist
| Color | Colorless, White, Gray, Yellowish | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous, adamantine on cleavage faces | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Transparent to translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 4–4.5 | 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. |
| Cleavage | Perfect on {010} | |
| Fracture | Conchoidal to uneven, brittle | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.42 | Ordinary rock-like heft (specific gravity about 2.42), similar to quartz. |
| Crystal system | Monoclinic |
Extra tests for Colemanite
Glass check. Colemanite 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.
Colemanite look-alikes and how to tell them apart
Colemanite is harder (Mohs 4–4.5) than Calcite (Mohs 3), so Colemanite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Colemanite vs Calcite →
Both sit near Mohs 4–4.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Colemanite vs Aragonite →
Quartz is harder (Mohs 7) than Colemanite (Mohs 4–4.5), so Quartz will scratch Colemanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Colemanite vs Quartz →
Analcime is harder (Mohs 5–5.5) than Colemanite (Mohs 4–4.5), so Analcime will scratch Colemanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
Colemanite identification FAQ
How can you tell if a rock is Colemanite?
Check the color (colorless, white, gray, and yellowish), the vitreous, adamantine on cleavage faces luster, a Mohs hardness of 4–4.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Colemanite?
Colemanite has a Mohs hardness of 4–4.5. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
What is the difference between Colemanite and Calcite?
Colemanite (Mohs 4–4.5, vitreous, adamantine on cleavage faces luster) and Calcite (Mohs 3, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Colemanite vs Calcite comparison for a side-by-side table.
Is Colemanite worth anything?
Entry-level Colemanite specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Colemanite?
Colemanite is most often colorless, white, gray, and yellowish. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
