Identifying Garnets Simplified
Identifying garnets by species is complicated. Learn how to use refractive index, hue, and absorption spectrum readings to simply the separation process.
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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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Donald Clark, CSM IMG
The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”
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