Diamond vs Opal
Diamond is harder (Mohs 10) than Opal (Mohs 5.5–6.5), so it resists scratching better; Opal is softer than quartz dust (7) and needs more care in everyday rings.
Diamond has the higher refractive index (2.417 vs 1.450), which a refractometer (over-the-limit reading) can use to separate them.
Diamond is denser (SG 3.52 vs 2.15); a diamond of the same size weighs about 64% more.
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| Property | Diamond | Opal |
|---|---|---|
| Species / material | Diamond (carbon) | Opal (hydrated silica) |
| Mohs hardness | 10 | 5.5–6.5 |
| Refractive index | 2.417 | 1.450 |
| Specific gravity | 3.52 | 2.15 |
| Crystal system | Cubic | Amorphous |
| Birefringence | None (isotropic) | None |
Values are typical ranges from standard gemmological references; individual stones can vary.
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