gems, garnet, color-change garnet, East Africa

Over the past 18 months, four exceptional change-of-color garnets from East Africa have been observed, notable for exhibiting a striking color shift similar to that of fine Russian alexandrite—green in daylight or fluorescent light and red under incandescent light. While East African color-change garnets have been known for years, most are either too dark or lack a dramatic shift, particularly when cut. GIA’s Research Department examined three of these remarkable stones, which showed refractive indices of 1.770 and 1.763. Spectroscopic analysis using a Beck prism spectroscope and a Pye Unicam UV-visible dual-beam spectrophotometer confirmed the presence of absorption features typical of pyrope-spessartine garnets. Semiquantitative chemical analysis via energy dispersive X-ray fluorescence (EDXRF) revealed compositions consistent with pyrope-spessartine garnets containing relatively high manganese levels. Interestingly, only a trace amount of chromium (0.1 wt.% Cr₂O₃) was detected, while the vivid color change was attributed almost entirely to more than 1 wt.% V₂O₃ (vanadium oxide) present in each sample.