Gemstones with RI 1.440
3 gemstones have a refractive index range that includes 1.440. Refractive index measures how much light bends when entering a gem — it's one of the most diagnostic properties for identification. Measured with a gemological refractometer.
| Gemstone | RI Range | SG Range | Crystal System | Optic Character |
|---|---|---|---|---|
| Black Opal | 1.440 – 1.460 | 2.09 – 2.16 | Amorphous | SR |
| Fire Opal | 1.370 – 1.470 | 1.98 – 2.20 | Amorphous | SR |
| Opal | 1.370 – 1.470 | 1.98 – 2.25 | Amorphous | SR |