Depósitos de alexandrita de Malacacheta, Minas Gerais.
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2000
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Abstract
Since 1975, alexandrite [Be(Al2-xCrx)2O4], the chromium-bearing crysoberyl variety, has been exploited
from alluvial and paleo-alluvial deposits in the Malacacheta region. The alluvial deposits consist of
resedimented gravel along the present drainage streams. The paleo-alluvial deposits are richer in alexandrite,
and show well-developed soil horizons covering the alexandrite-bearing gravel layer. Alexandrite grains
show angular shapes with very sharp edges, suggesting transport for short distances. The country rocks are
quartz-mica schist and peraluminous mica schist (Salinas Formation), covered by alternating mica schist
and quartzite layers (Capelinha Formation). Both formations are of Neoproterozoic age. They host tectonic
slabs of metaultramafic rocks, and are cut by intrusive granites of Cambrian age. No alexandrite-bearing
rock has been found in the area, probably due to the intense tropical weathering. However, some of the
mapped rocks are sources for Be (granites), Cr (metaultramafics) and Al (peraluminous schists), the essential
elements for alexandrite crystallization. We suggest a metasomatic system of Cambrian age for alexandrite
genesis in the area, involving the interaction of granite-related Be-rich fluids with metaultramafic rocks
and peraluminous schists.
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Citation
BASÍLIO, M. S.; SOARES, A. C. P.; EVANGELISTA, H. J. Depósitos de alexandrita de Malacacheta, Minas Gerais. Geonomos, Belo Horizonte, v. 8, n.1, p. 47-54, 2000. Disponível em: <https://periodicos.ufmg.br/index.php/revistageonomos/article/view/11581>. Acesso em: 20 de jun. 2017.