40 km NE of the Carnaiba deposit
are in a block of metamorphosed ultramafic and volcanic rocks 3.5 km long and about 500 m wide, enclosed in adamellite granites of the late Proterozoic Campo Formoso massif. Dolomitized serpentinites, talc rocks, and amphibolites of this large xenolith host pegmatite veins and metasomatic zones of biotite-phlogopite rocks with light-green beryl
associated with scheelite, molybdenite, phenakite, chromite and tourmaline. The physical properties, chemical composition and inclusions of the Socoto emeralds
are similar to those of the Carnaiba deposit
. Their typomorphic features are inclusions of carbonates (calcite, dolomite, breunnerite), thin tube-shaped channels, and finely-banded, zoned colour (Eidt and Schwarz, 1990).
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 91