146 RAPID COMMUNICATIONS GEMS & GEMOLOGY SUMMER 2007

showed one of the authors (BML) some yellowish green crystals that he purchased as diopside while on buy-ing trips to Tanzania in August and November 2005. The material was reportedly produced during this time period from Block D at Merelani, in the same area that yielded some large tsavorite gem rough (see Laurs, 2006). Mr. Ula-towski obtained 1,200 grams of the green crystals, mostly as broken pieces ranging from 0.1 to 50 g (typically 1–5 g). More recently, in May 2007, he obtained some additional pieces of gem-quality material weighing 0.1–2 g. The “mint ” green color is quite attractive, but most of the rough is not cuttable due to the presence of cleavage planes and, in some cases, the flat morphology of the crys-tal fragments. In 2006, Mr. Ulatowski was informed by a few of his customers that the flatter crystals might be tremolite, rather than diopside. This was consistent with the dia-mond-shaped cross-section of these crystals (typical of an amphibole), which was distinct from the blocky cross-sec-tion (typical of diopside, which is a pyroxene) shown by other crystals in the parcels. Mr. Ulatowski loaned one example of both types of crystals to GIA for examination (figure 1), and we also Figure 1. These yellowish green crystals were recov-ered from Block D at Merelani in the latter part of 2005. A blocky morphology is shown by the diopside crystal (1.6 cm tall; left and bottom), whereas the tremolite crystal has a flattened, diamond-shaped cross-section. Photos by Robert Weldon