Ruby vs Garnet: How to Tell Them Apart
Red garnet is singly refractive while ruby is doubly refractive, and ruby is much harder, so the two separate easily with a polariscope.
| Property | Ruby | Garnet (pyrope / almandine) |
|---|---|---|
| Mineral | Corundum (Al2O3) | Garnet group silicate |
| Typical colours | Pinkish red to deep red | Red, deep red, purplish red (rhodolite) |
| Mohs hardness | 9 | 6.5–7.5 |
| Toughness | Excellent | Good |
| Refractive index | 1.762–1.770 | 1.730–1.810 |
| Birefringence | 0.008 | None (singly refractive) |
| Optic character | Uniaxial – | Isotropic |
| Specific gravity | 3.95–4.03 | 3.65–4.30 |
| Pleochroism | Strong (purplish red / orangey red) | None (singly refractive) |
| Common treatments | Heat treatment is very common; lead-glass filling and diffusion also occur | Normally untreated |
| Ultrasonic cleaning | Use caution | Generally safe |
How to tell Ruby from Garnet
- DecisivePolariscope. Garnet (pyrope / almandine) is singly refractive and stays dark as you rotate it between crossed polarisers; Ruby is doubly refractive and blinks light and dark four times per turn (single-crystal stones).
- HelpfulDichroscope. Pleochroism differs: Ruby is Strong (purplish red / orangey red); Garnet (pyrope / almandine) is None (singly refractive).
- WeakRefractometer. The refractive index ranges overlap (Ruby 1.762–1.770 vs Garnet (pyrope / almandine) 1.730–1.810), so RI alone cannot separate them.
- WeakSpecific gravity. The SG ranges overlap (3.95–4.03 vs 3.65–4.30), so SG alone cannot separate them.
- NoteDurability. Ruby (Mohs 9) is harder than Garnet (pyrope / almandine) (Mohs 6.5–7.5). Do not scratch-test a stone you want to keep.
- NoteTreatments. Ruby: Heat treatment is very common; lead-glass filling and diffusion also occur. Garnet (pyrope / almandine): Normally untreated.
Ruby vs Garnet for jewellery
Ruby has a Mohs hardness of 9 and excellent toughness; Garnet (pyrope / almandine) has a Mohs hardness of 6.5–7.5 and good toughness.
Red garnet is far more affordable than ruby. Ruby is the better choice for hard-wearing rings, while garnet suits budget-friendly everyday pieces.
Educational reference only. Typical published values vary between specimens and sources, and this page is not a gemological laboratory report. Confirm important stones with a recognised gem lab.
Frequently asked questions
What is the main difference between Ruby and Garnet?
Red garnet is singly refractive while ruby is doubly refractive, and ruby is much harder, so the two separate easily with a polariscope.
How can I tell Ruby from Garnet?
Polariscope: Garnet (pyrope / almandine) is singly refractive and stays dark as you rotate it between crossed polarisers; Ruby is doubly refractive and blinks light and dark four times per turn (single-crystal stones).
Which is harder, Ruby or Garnet?
Ruby is harder: it is Mohs 9, while Garnet (pyrope / almandine) is Mohs 6.5–7.5.
Which is more durable for everyday jewellery, Ruby or Garnet?
Ruby has a Mohs hardness of 9 and excellent toughness; Garnet (pyrope / almandine) has a Mohs hardness of 6.5–7.5 and good toughness. Toughness describes resistance to chipping and breaking, which matters as much as hardness for rings.
What are the refractive index and specific gravity of Ruby and Garnet?
Ruby: refractive index 1.762–1.770, specific gravity 3.95–4.03. Garnet: refractive index 1.730–1.810, specific gravity 3.65–4.30.
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