RocksdayCorundum vs Garnet
How to tell them apart
Aluminum oxide and the second-hardest natural mineral. Red corundum is ruby; every other color is sapphire.
Photo: Ra'ike (see also Ra'ike on de.wikipedia, CC BY-SA 3.0
A family of silicate minerals that grow as round, many-faced crystals. Deep red almandine studding schist is the classic find.
Photo: Moha112100, CC BY-SA 3.0
Quick tests
- Hardness: Corundum is clearly harder: Mohs 9 versus 7–7.5.
Key differences
- Garnet is softer (7–7.5) and forms rounded dodecahedra.
- Ruby is harder (9) and grows in six-sided barrels, not balls.
Side by side
| Property | Corundum | Garnet |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 9 | 7–7.5 |
| Luster | Adamantine to vitreous | Vitreous |
| Streak | White | White |
| Colors | Red, Blue, Pink, Gray | Red, Brown |
| Crystal system | Trigonal | Cubic |
| Specific gravity | 3.95–4.1 | 3.9–4.3 |
| Formula | Al₂O₃ | Fe₃Al₂(SiO₄)₃ (almandine) |
| Found in | Mogok, Myanmar; Sri Lanka | Gore Mountain, New York; Emerald Creek, Idaho |
Properties that are the same for both are grayed out.
How to identify corundum
- Hardness 9 — scratches everything except diamond.
- Barrel-shaped six-sided crystals.
- Heavy for a non-metallic stone.
- Often shows flat parting planes.
Crystal system: Trigonal
Full Corundum guide →How to identify garnet
- Ball-shaped crystals with 12 or 24 faces.
- Deep wine-red to brown.
- Scratches glass.
- Often embedded in mica schist.
Crystal system: Cubic
Full Garnet guide →More comparisons
Could you tell them apart from a blurry close-up?
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