A large Brazilian source of emeralds
, Santa Terezinha, was discovered in 1981 about 275 km north of Goiana in the state of Goias.
mineralization is developed in the talc schists alternating with the hematite schists and quiartzites, which are crumpled into large isoclinal folds. Rich and extensive emerald-bearing zones with thickness of several meters have been traced to a depth fo 100 m. The emeralds
are mined at several sections. The richest emerald
area is a periclinal closure of the fold structure, where the most of the pegmatite bodies are concentrated. In the upper section, a large quantity of emeralds
was extracted from clayey eluvial deposits of an ancient weathered crust, where emerald
is enclosed in a dense limonite envelope.
crystals are of limited size and seldom exceed 1 cm in length. Faceted stones of good quality usually have a weight of less than 1 ct. Emerald
is characterized by high content of chromium, iron, magnesium and sodium. Density may reach 2.87 g/cm³. Pleochroism is dark and bluish green to pale yellowish green. The most common inclusions are pyrite, carbonates (dolomite, ferroan magnesite), with lesser talc, magnesioferrite, chrome spinels and mica (Cassedanne and Sauer, 1984).
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 92
Gem list contains entries from all listed localities in region.
Localities in this Region
- Santa Terezinha de Goiás district