RocksdayColemanite vs Quartz
How to tell them apart
A calcium borate forming glassy crystals inside geode-like nodules in desert lake beds.
Photo: Bureau of Mines, Public domain
The second most abundant mineral in Earth's crust. Clear crystals grow as six-sided prisms capped by a pointed termination, and quartz shows up as grains in sand, granite and countless other rocks.
Photo: Didier Descouens, CC BY-SA 4.0
Quick tests
- Scratch glass: Quartz scratches glass (Mohs 7); Colemanite can't (Mohs 4–4.5).
Key differences
- Quartz is harder.
Side by side
| Property | Colemanite | Quartz |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 4–4.5 | 7 |
| Luster | Vitreous | Vitreous |
| Streak | White | White |
| Colors | Clear, White, Gray | Clear, White, Gray |
| Crystal system | Monoclinic | Trigonal |
| Specific gravity | 2.42 | 2.65 |
| Formula | CaB₃O₄(OH)₃·H₂O | SiO₂ |
| Found in | Death Valley, California; Bigadiç, Turkey | Hot Springs, Arkansas; Minas Gerais, Brazil |
Properties that are the same for both are grayed out.
How to identify colemanite
- Clear to white glassy crystals in nodules.
- Hardness about 4.
- Light in weight.
Crystal system: Monoclinic
Full Colemanite guide →How to identify quartz
- Scratches glass easily and can't be scratched by a steel knife.
- Six-sided prisms with pointed ends when it forms crystals.
- Breaks with curved, shell-like (conchoidal) fractures — no flat cleavage planes.
- Does not fizz in vinegar or dilute acid.
Crystal system: Trigonal
Full Quartz guide →More comparisons
Could you tell them apart from a blurry close-up?
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