Ruby vs Spinel
Ruby and Spinel are easy to confuse. Here’s how they stack up on the properties that actually separate them.
| Ruby | Spinel | |
|---|---|---|
| Also known as | Corundum (Corundum family) | — |
| Colour | Red | Red, Blue, Black, Pink, Purple |
| Mohs hardness | 9.0 | 7.5–8.0 |
| Lustre | Subadamantine, vitreous, pearly (on partings) | Vitreous |
| Streak | White | White |
| Crystal system | Trigonal | Cubic |
| Transparency | Transparent, translucent | Transparent to opaque |
| Cleavage | No true cleavage | None |
| Fracture | Conchoidal, splintery | Conchoidal |
| Chemical formula | Aluminum oxide with chromium, AlO:Cr | — |
| Specific gravity | 3.97–4.05 | (Depending on the composition) The rare Zn-rich spinel can be as high as 4.40, otherwise it averages from 3.58 to 3.61 |
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Frequently asked questions
What's the easiest way to tell Ruby from Spinel?
Hardness is the quickest test: Ruby is Mohs 9.0 and Spinel is Mohs 7.5–8.0.