RocksdayOlivine vs Willemite
How to tell them apart
Olive-green silicate that makes up most of Earth's upper mantle. Gem-quality olivine is called peridot.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
A zinc silicate that glows an intense green under shortwave UV.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Key differences
- Olivine doesn't fluoresce.
Side by side
| Property | Olivine | Willemite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6.5–7 | 5.5 |
| Luster | Vitreous | Vitreous to resinous |
| Streak | White | White |
| Colors | Green, Yellow | Green, White, Brown |
| Crystal system | Orthorhombic | Trigonal |
| Specific gravity | 3.2–4.4 | 3.9–4.2 |
| Formula | (Mg,Fe)₂SiO₄ | Zn₂SiO₄ |
| Found in | Papakōlea, Hawaii; San Carlos, Arizona | Franklin and Sterling Hill, New Jersey; Arizona |
Properties that are the same for both are grayed out.
How to identify olivine
- Bottle- to olive-green glassy grains.
- Often as sugary green clumps in black basalt.
- No cleavage — breaks like glass.
- Hard enough to scratch glass.
Crystal system: Orthorhombic
Full Olivine guide →How to identify willemite
- Dull green or brown in daylight.
- Brilliant green glow under shortwave UV.
- Often with red-glowing calcite and black franklinite.
Crystal system: Trigonal
Full Willemite guide →More comparisons
Could you tell them apart from a blurry close-up?
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