Emerald
mineralization occurs in association with small recrystallized pegmatitic bodies hosted by metamorphosed
ultramafic rocks within the Santa Monica Shear Zone. Prospecting and exploration have
been carried out in a few small pits and tunnels, producing emerald crystals with transparent areas
that typically range between 2 and 5 mm. Polished samples typically show a saturated bluish green
color with a medium-light to medium tone. The most common internal features are partially healed
fissures with two-phase (liquid-gas) fluid inclusions and a variety of fine, parallel-oriented growth
tubes. The emeralds contain moderate amounts of the chromophore elements Cr and Fe, and traces
of V; they also show relatively high K and low Li. FTIR spectroscopic features are consistent with
alkali-bearing emeralds that contain considerable CO2 and a small amount of deuterated water.
Emeralds from Fazenda Bonfim can be distinguished from those of other schist- and pegmatite-related
commercial deposits.