Miracle at Merelani: A remarkable occurrence of graphite, diopside and associated minerals from the Karo Mine, Block D, Merelani Hills, Arusha Region, Tanzania

The gem mines of the Merelani Hills, Arusha Region, Tanzania (fig. 1), are well known for tanzanite, the purple-blue gem variety of zoisite first discovered there in the 1960s. Other gem-quality minerals have since been mined at the locality, including crystals of the mint-green grossular known as tsavorite and lustrous green prismatic crystals of diopside. As modern mining methods at TanzaniteOne Mining Ltd. (Arusha, Tanzania) expand in Block C, and as more primitive mining methods continue in Blocks A, B, and D, fine-quality gem specimens and interesting mineral specimens continue to be available. A comprehensive review of the history, geology, and mineralogy of these mines has been given by Wilson et al. (2009)