Gemstones with RI 1.720

10 gemstones have a refractive index range that includes 1.720. 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.

← All RI Values

GemstoneRI RangeSG RangeCrystal SystemOptic Character
Black Spinel1.712 – 1.7303.58 – 3.61CubicSR
Taaffeite1.719 – 1.7233.59 – 3.63HexagonalDR_U-
Diaspore1.685 – 1.7523.30 – 3.39OrthorhombicDR_B+
Kyanite1.712 – 1.7343.53 – 3.68TriclinicDR_B-
Spinel1.712 – 1.7363.57 – 3.63CubicSR
Rhodochrosite1.600 – 1.8203.40 – 3.70TrigonalDR_U-
Rhodonite1.716 – 1.7523.57 – 3.76TriclinicDR_B+
Chrome Diopside1.664 – 1.7303.22 – 3.38MonoclinicDR_B-
Star Diopside1.664 – 1.7213.27 – 3.36MonoclinicDR_B-
Malachite1.655 – 1.9093.60 – 4.05MonoclinicDR_B-
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