Feature Gems & Gemology, Spring 1984, Vol. 20, No. 1

The Santa Terezinha De Goias Emerald Deposit

The Santa Terezinha de Goias emerald deposit, currently the most important source of emeralds in Brazil, lies northwest of Brasilia, in the State of Goias. The emeralds, most of which are stones of a carat or less, occur in a talc schist layer intersected by pegmatite. The emeralds are recovered by independent miners via trenches, pits, and tunnels at two prospects: Trecho Novo and Trecho Velho. The grade of the ore is: 1 to 6 parts of emeralds to 10,000 parts of ore. The density of the gems is 2.70; the refractive indexes are 1.580 and 1.588, with greenish dark blue/yellowish pale green pleochroism. The spectrum is typical, with two strong lines and two partial absorption bands; there is no fluorescence; pyrite and chromite are the most typical inclusions, with calcite crystals present in minor amounts.