Gemstones with RI 1.645
13 gemstones have a refractive index range that includes 1.645. 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 |
|---|---|---|---|---|
| Chrome Tourmaline | 1.624 – 1.660 | 3.00 – 3.20 | Trigonal | DR_U- |
| Clinohumite | 1.625 – 1.675 | 3.13 – 3.35 | Monoclinic | DR_B+ |
| Andalusite | 1.629 – 1.649 | 3.13 – 3.21 | Orthorhombic | DR_B- |
| Apatite | 1.628 – 1.649 | 3.17 – 3.23 | Hexagonal | DR_U- |
| Prehnite | 1.611 – 1.665 | 2.82 – 2.94 | Orthorhombic | DR_B+ |
| Green Tourmaline | 1.616 – 1.650 | 3.00 – 3.10 | Trigonal | DR_U- |
| Watermelon Tourmaline | 1.616 – 1.650 | 3.00 – 3.10 | Trigonal | DR_U- |
| Jet | 1.640 – 1.680 | 1.10 – 1.40 | Amorphous | SR |
| Turquoise | 1.610 – 1.650 | 2.60 – 2.90 | Triclinic | AGG |
| Pearl | 1.520 – 1.690 | 2.60 – 2.85 | Aggregate | AGG |
| Lapis Lazuli | 1.500 – 1.670 | 2.70 – 2.90 | Aggregate | AGG |
| Rhodochrosite | 1.600 – 1.820 | 3.40 – 3.70 | Trigonal | DR_U- |
| Coral | 1.486 – 1.658 | 2.60 – 2.70 | Aggregate | AGG |