Belmont mine, Itabira, Minas Gerais, Brazil
Since 1978, the Belmont mine has been operating 13 km SE of the town of Itabira.Belmont Mine is in about 2 m thick emerald-bearing biotite-phlogopite glimmerite zone, which is elongated along the contact of quartz-mica schists and migmatites (banded gneisses). The average emerald content in the glimmerites is one of the highest in Brazil.
Solid inclusions in the emerald crystals are predominantly biotite and phlogopite, with lesser amounts of quartz, tremolite, dolomite, andesine, and apatite. Thin needle-like channels, parallel to the long crystal axis, are characteristic and may produce a rain-like structure and silky lustre. The emerald density is 2.72 - 2.74 g/cm³.
Ref: E.Ya. Kievlenko (2003) Geology of gems, pp. 92 - 94