Gemstones with RI 1.780
7 gemstones have a refractive index range that includes 1.780. 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 |
|---|---|---|---|---|
| Benitoite | 1.757 – 1.804 | 3.64 – 3.68 | Hexagonal | DR_U+ |
| Malachite | 1.655 – 1.909 | 3.60 – 4.05 | Monoclinic | DR_B- |
| Low-Type Zircon | 1.780 – 1.815 | 3.90 – 4.10 | Tetragonal | SR |
| Almandine Garnet | 1.770 – 1.830 | 3.93 – 4.30 | Cubic | SR |
| Star Garnet | 1.770 – 1.830 | 3.93 – 4.30 | Cubic | SR |
| Malaya / Umbalite Garnet | 1.730 – 1.780 | 3.65 – 3.87 | Cubic | SR |
| Rhodochrosite | 1.600 – 1.820 | 3.40 – 3.70 | Trigonal | DR_U- |