RocksdayCryolite vs Fluorite
The quickest way to tell Cryolite from Fluorite: A fingernail scratches Cryolite (Mohs 2.5) but not Fluorite (Mohs 4).
A rare sodium-aluminum fluoride. The only large deposit, at Ivittuut in Greenland, was mined until 1987 as the flux that made aluminum smelting practical.
Photo: Didier Descouens, CC BY-SA 3.0
A colorful mineral that grows as cubes and splits into octahedrons. Many specimens glow under ultraviolet light — the word 'fluorescence' was coined from it.
Photo: CarlesMillan, CC BY-SA 3.0
Quick tests
- Fingernail: A fingernail scratches Cryolite (Mohs 2.5) but not Fluorite (Mohs 4).
Key differences
- Fluorite cleaves into octahedrons and is harder (4).
Side by side
| Property | Cryolite | Fluorite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 2.5 | 4 |
| Luster | Vitreous to greasy | Vitreous |
| Streak | White | White |
| Colors | White, Clear, Gray | Purple, Green, Blue, Yellow, Clear |
| Crystal system | Monoclinic | Cubic |
| Specific gravity | 2.95–3 | 3.18 |
| Formula | Na₃AlF₆ | CaF₂ |
| Found in | Ivittuut, Greenland | Cave-in-Rock, Illinois; Weardale, England |
Properties that are the same for both are grayed out.
How to identify cryolite
- Colorless to white, waxy masses.
- A fingernail barely scratches it.
- Powdered in water, it nearly disappears — its refractive index is close to water's.
Crystal system: Monoclinic
Full Cryolite guide →How to identify fluorite
- Cubic crystals, often with color zoning in purple and green.
- Cleaves into eight-sided octahedral fragments.
- Hardness 4 — a knife scratches it, but a coin doesn't.
- Often glows blue or violet under a UV flashlight.
Crystal system: Cubic
Full Fluorite guide →More comparisons
Frequently asked questions
What is the difference between cryolite and fluorite?
Cryolite is a mineral (Na₃AlF₆) with a Mohs hardness of 2.5 and a vitreous to greasy luster, usually white, colorless or gray. Fluorite is a mineral (CaF₂) with a Mohs hardness of 4 and a vitreous luster, usually purple, green, blue, yellow or colorless.
How can you tell cryolite from fluorite?
A fingernail scratches Cryolite (Mohs 2.5) but not Fluorite (Mohs 4). Fluorite cleaves into octahedrons and is harder (4).
Could you tell them apart from a blurry close-up?
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