GEMS & GEMOLOGY WINTER 2009 emantoid is the Cr-bearing yellowish green to green variety of andradite [Ca3Fe2(SiO4)3] (O’Donoghue, 2006). Very popular in Russia (where it was first discovered) from about 1875 to the start of the Russian Revolution in 1917, this gem has enjoyed a resurgence in demand since the beginning of the 21st century (Furuya, 2007). One of the most notable localities for demantoid is Val Malenco, located in Sondrio Province in the Lombardy region of northern Italy. Several deposits in this area have produced well-formed rhombic dodecahedral crystals (e.g., figure 1, left) that are coveted by collectors (Bedogne and Pagano, 1972; Amthauer et al., 1974; Bedogne et al., 1993, 1999). A limited quantity (some thousands of carats) of Val Malenco demantoids have been cut, producing gemstones that are attractive but rarely exceed 2 or 3 ct (e.g., figure 1, right). Val Malenco demantoid was first documented by Cossa (1880), who studied a sample recovered by T. Taramelli in 1876. In the next century, Sigismund (1948) and Quareni and De Pieri (1966) described the morphology and some physical and chemical properties of this garnet. Subsequently, the demantoid was investigated by Bedogne and Pagano (1972), Amthauer et al. (1974), Stockton and Manson (1983), and Bedogne et al. (1993, 1999). Because some of these data are more than 20 years old, and some publications are in Italian, we prepared this review and update on the physical, chemical, and gemological properties of demantoid from Val Malenco. Note that demantoid—although commonly used as a trade or variety name—is not approved by the International Mineralogical Association as a mineral name (Nickel and Mandarino, 1987; O’Donoghue, 2006). However, for reasons of brevity and consistent with gemological convention, throughout this article we will use demantoid instead of andradite, variety demantoid.