gems, jade, Transvaal jade, hydrogrossular garnet, jade imitation

At the Pueblo show, Tom Schneider of TMS Gems (San Diego, California) offered “Transvaal jade” rough with an exceptionally vivid green color. Also known as “African jade” or “South African jade,” this material is not true jade (jadeite or nephrite) but rather a grossular garnet whose trade name is based on its massive form, green hue, and origin. Typically, such material is more translucent and lighter in color. The sample, opaque and green within a fine-grained chromite matrix, had a refractive index of 1.731 and was inert to both long- and short-wave UV radiation. Identified as grossular garnet by Raman spectroscopy, it was further classified as grossular-andradite by X-ray fluorescence analysis and the 1995 naming convention. Chemically, the specimen consisted of 80.83 mol.% grossular (Ca₃Al₂Si₃O₁₂), 10.50 mol.% uvarovite (Ca₃Cr₂Si₃O₁₂), 7.11 mol.% andradite (Ca₃Fe₂Si₃O₁₂), and trace other garnets. Garnets in this range typically show Fe₂O₃ contents of 4.64–20.91 wt.% and Cr₂O₃ ≤0.23 wt.%, but this sample showed low iron (2.49 wt.% Fe₂O₃) and high chromium (3.50 wt.% Cr₂O₃), accounting for its vivid green color. Chromium, and possibly vanadium, contributes to this intense hue, while iron imparts yellow to brown tones. The resulting coloration and high-polish luster made this chromium-rich grossular a particularly striking example of its kind.