Discovery and Characterisation of ‘Jaguar' Quartz from Tanzania

Two quartz varieties sold as ‘Jaguar' quartz entered the gem market in early 2023 from the Mpwapwa District, Dodoma Region, Tanzania. This material consists of rock crystal or rose quartz with conspicuous dark-coloured inclusions that display prismatic to rounded morphologies, and frequently show a preferential orientation within the host materials. The inclusions in the rock crystal consist of dark brown, tabular to pseudo-hexagonal crystals of phlogopite, while those in the rose quartz are mainly comprised of dark green to black prismatic crystals of magnesio-hornblende. Textural and chemical evidence indicate a syngenetic origin between the inclusions and quartz hosts, with the mica probably crystallising during early fluid-rich stages and the calcic amphibole forming subsequently under higher-temperature, amphibolite-facies conditions. The inclusions record the evolution of a hydrous Fe-Mg-Ca-bearing fluid linked to metamorphic processes in the Mpwapwa terrane. The limited occurrence and distinctive mineralogical signature of ‘Jaguar' quartz make it a unique and traceable gem material within the family of included quartzes.