Identifying Garnets Using Three Factors

You can use the refractive index (RI), hue, and absorption spectrum of your garnet specimen to make your identification.

Species RI Hue Absorption
Andradite 1.880 – 1.895 Very slightly yellowish green through orangey yellow None except demantoid, which shows a cut off at 440-445 nm. May have bands at 618 and 634. Demantoid may have thin bands at 685 and 690.
Grossular 1.730 – 1.760 All colors, including colorless, except blue. None except highly saturated orange which show bands at 407 and or 430 nm. May show general absorption on blue end.
Pyrope 1.714 – 1.742 Purplish red through reddish orange and colorless Usually a cut off at 440 to 445 nm and a broad band at 564 nm. None when colorless. Some with weak bands for almandine or spessartite components.
Pyrope/almandine 1.742 – 1.785 Reddish orange through red purple Shows almandine spectra.
Almandine 1.785 – 1.830 Orangish red through purplish red. Bands at 504, 520 and 573 nm. May have weak bands at 423, 460, 610 and 680-690.
Almandine/spessartite 1.810 – 1.820 Reddish orange through orange red. Cut off to 435, bands at 460, 480, 504, 520, and 573 nm. Merging of

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