gems, inclusions, beryl, emerald, Brazil, Santa Terezinha de Goiás

Hänni and Kerez report gemological and mineralogical investigations of emerald crystals and host rocks from the then-new Santa Terezinha de Goiás deposit in Brazil. The emeralds occur as hexagonal prismatic crystals in talc and biotite schists and range from light to dark green, commonly with a bluish cast. Refractive indices range from 1.585–1.587 to 1.592–1.595, birefringence from 0.006 to 0.008, and specific gravity from 2.752 to 2.764. Electron-microprobe examination identified characteristic solid inclusions of dolomite and picotite (chromian spinel). Many crystals contain internal fractures but lack the liquid films or feather-like inclusions typical of some other emerald deposits. The authors also describe mining conditions: the original southern workings had been largely abandoned in favor of better material found about 500 m to the north, where numerous small claims were worked by blasting and the material transported to washing sites on the Rio Peixe.