Feature Gems & Gemology, Winter 2009, Volume 45, No. 4

Demantoid from Val Malenco, Italy: Review and Update

New data are presented for demantoid from Val Malenco, Italy, as obtained by classical gemological methods, electron microprobe and LA-ICP-MS chemical analyses, and UV-Vis-NIR and mid-IR spectroscopy. The results confirmed that these garnets are almost pure andradite (≥98 mol%, RI>1.81, SG = 3.81–3.88). All 18 samples studied contained “horsetail” inclusions, which are characteristic of a serpentinite geologic origin. Fe and Cr control the coloration of demantoid, though color variations in these samples were mainly correlated to Cr content.