Feature Gems & Gemology, Winter 1983, Vol. 19, No. 4

Gem Andradite Garnets

Andradite, the rarest of the five well-known gem garnet species, is examined and characterized with respect to refractive index, specific gravity, absorption spectrum, color, and chemical composition. These properties are measured and specifically tabulated for 21 gem andradrites (20 green and one yellow). From the narrow ranges of refractive index (1.880-1.883), specific gravity (3.80-3.88), and chemical composition (less than 3% of components other than andradite in any of the specimens examined) that were observed, it is apparent that the gem-quality andradrites are chemically distinct from other types of gem garnets and that these stones are easy to distinguish by means of color coupled with refractive index.