Identification guide · Hydroxide Minerals
How to Identify Brucite
Brucite is usually white, pale green, and pale blue with a vitreous luster and is translucent. It has a Mohs hardness of 2.5. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Its streak is white. It is most often confused with Calcite, Aragonite, and Dolomite; the tests below separate them.
Brucite identification checklist
| Color | White, Pale green, Pale blue, Yellow, Gray | 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 | Translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 2.5 | 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 basal | |
| Fracture | Uneven | |
| Specific gravity | 2.4 | Ordinary rock-like heft (specific gravity about 2.4), similar to quartz. |
| Crystal system | Trigonal |
Brucite look-alikes and how to tell them apart
Both sit near Mohs 2.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Brucite vs Calcite →
Aragonite is harder (Mohs 3.5–4) than Brucite (Mohs 2.5), so Aragonite will scratch Brucite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Brucite vs Aragonite →
Dolomite is harder (Mohs 3.5–4) than Brucite (Mohs 2.5), so Dolomite will scratch Brucite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Brucite vs Dolomite →
Magnesite is harder (Mohs 4) than Brucite (Mohs 2.5), so Magnesite will scratch Brucite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
Field tips
- Look for a soft, light-colored mineral with perfect basal cleavage that yields flexible but inelastic sheets.
- Brucite has a pearly luster on cleavage faces and a noticeably low density for its size.
- Distinguish it from mica by its inelastic sheets and from gypsum by its association with serpentine and dolomite.
Brucite identification FAQ
How can you tell if a rock is Brucite?
Check the color (white, pale green, pale blue, and yellow), the vitreous luster, a Mohs hardness of 2.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Brucite?
Brucite has a Mohs hardness of 2.5. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
What is the difference between Brucite and Calcite?
Brucite (Mohs 2.5, vitreous luster) and Calcite (Mohs 3, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Brucite vs Calcite comparison for a side-by-side table.
Is Brucite worth anything?
Entry-level Brucite specimens sell for around $5, typical collector pieces about $40, and premium examples $250 or more depending on size, quality and locality.
What color is Brucite?
Brucite is most often white, pale green, pale blue, and yellow. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
