Purple Mozambique Garnet

by Dr. W. Zhou, first published in Facette 23 (February 2017)

In early 2016, attractive bright purple garnets arrived at SSEF (Figure 1) in Bangkok, Basel and Hong Kong. Based on client information, they are from a new mine, Padagaga in the Chimoio area in Mozambique, which was discovered recently (Schwarz, 2016).

After routine gemmological testing, the chemistry of these garnets fits with rhodolite, within the solid solution series pyrope (Mg₃Al₂Si₃O₁₂) – almandine (Fe₃Al₂Si₃O₁₂). EDXRF analysis shows main chemical composition is around: Fe₂O₃ 27%, MgO 17%, Al₂O₃ 19% and SiO₂ 36% with minor amounts of CaO and MnO. Comparing this to published data (Lind, 2015, Schwarz, 2016 and Sangsawong 2016), the UV-Vis spectra (Figure 2) shows Fe²⁺ absorptions that dominate (around 500-700 nm, especially the ones from 500-600 nm) together with a mixture of Mn²⁺ (ca. 410 nm), while the contribution of V³⁺ + Cr³⁺ (420 to 430 nm and 515-530 nm) is relatively low.

Since this new material only recently appeared on the market, further studies are required to entirely understand the gemmological differences between this and stones from traditional localities like Tanzania and Malawi. We look forward to seeing many more such charming purple rhodolite garnets in the SSEF.