Gems & Gemology, Winter 2009, Volume 45, No. 4
Demantoid from Val Malenco, Italy: Review and Update
Ilaria Adamo, Rosangela Bocchio, Valeria Diella, Alessandro Pavese, Pietro Vignola, Loredana Prosperi, and Valentina Palanza
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.