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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By Donald Clark, CSM IMG, updated on December 20, 2022

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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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
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Donald Clark, CSM IMG

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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By Donald Clark, CSM IMG, updated on December 20, 2022

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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Identifying Garnets Simplified