RocksdayRuby vs Spinel
How to tell them apart
Red corundum, colored by chromium. After diamond it's the hardest natural gemstone.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
A hard magnesium aluminum oxide that forms sharp octahedral crystals — long confused with ruby.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Key differences
- Red spinel is singly refractive and forms octahedrons.
- Ruby is harder, forms hexagonal crystals and is doubly refractive.
Side by side
| Property | Ruby | Spinel |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 9 | 7.5–8 |
| Luster | Adamantine to vitreous | Vitreous |
| Streak | White | White |
| Colors | Red, Pink | Red, Pink, Blue, Purple, Black |
| Crystal system | Trigonal | Cubic |
| Specific gravity | 3.97–4.05 | 3.58–3.61 |
| Formula | Al₂O₃ (with chromium) | MgAl₂O₄ |
| Found in | Mogok, Myanmar; Montepuez, Mozambique | Mogok, Myanmar; Badakhshan, Tajikistan |
Properties that are the same for both are grayed out.
How to identify ruby
- Red to pinkish red, often in six-sided barrel crystals.
- Hardness 9 — scratches topaz and quartz.
- Glows red under a UV light.
Crystal system: Trigonal
Full Ruby guide →How to identify spinel
- Sharp eight-sided octahedrons, often in marble.
- Hardness about 8.
- Red, pink, blue or purple with a bright glassy luster.
Crystal system: Cubic
Full Spinel guide →More comparisons
Could you tell them apart from a blurry close-up?
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