Pampa Branca — A Minas Gerais Pegmatite for Chrysoberyl
Pampa Branca — A Minas Gerais Pegmatite for Chrysoberyl
Brazilian deposit producing cat's-eye chrysoberyl and minor alexandrite
Pampa Branca is a pegmatite locality in the state of Minas Gerais, Brazil, recorded in gemmological literature for its production of chrysoberyl, including cat's-eye material and occasional alexandrite. The deposit is part of the broader Eastern Brazilian Pegmatite Province, the great gem-bearing belt that has supplied the world with aquamarine, tourmaline, topaz, and chrysoberyl since the eighteenth century. Pampa Branca is less famous than the alexandrite-defining Hematita locality further north, but it remains a documented source for chrysoberyl in the Brazilian gem trade.
Geological setting
Like most Minas Gerais gem pegmatites, the Pampa Branca pegmatites intrude older metamorphic rocks of the São Francisco craton margin and crystallised from beryllium-, lithium-, and tantalum-rich residual melts. Chrysoberyl, with the composition BeAl2O4, forms in the late stages of pegmatite crystallisation where beryllium and aluminium are concentrated and silica activity is low enough to preclude beryl. Where chromium enters the structure in trace amounts, the strong colour change between daylight and incandescent light known as the alexandrite effect can develop.
Pampa Branca chrysoberyl is recovered both from primary pegmatite veins and from surrounding eluvial and alluvial concentrates. Mining is artisanal in character, conducted by small operators and cooperatives, in line with the broader pattern of small-scale Minas Gerais gem mining.
Material from the deposit
The most consistent product from Pampa Branca is yellow to greenish-yellow chrysoberyl, faceted as a transparent collector and jewellery stone, and chatoyant cat's-eye chrysoberyl cut as cabochon. Cat's-eye material from the deposit can show the sharp single eye and milky-honey body colour that defines fine cymophane. Alexandrite, when it occurs, tends to show a partial colour change rather than the intense red-to-green effect of the best Hematita and Russian material, and sizes are generally modest.
Hardness at 8.5 makes chrysoberyl from any source robust enough for everyday wear, including ring use. Refractive indices around 1.746 to 1.755 and a specific gravity near 3.71 are consistent across the species.
In the trade
Pampa Branca rarely appears as a labelled provenance in retail. Chrysoberyl from the deposit moves through Brazilian dealers and reaches international markets as Brazilian chrysoberyl without further specification. For Skyjems buyers, the practical consideration is the quality of the individual stone — saturation of yellow body colour, sharpness of cat's-eye, completeness and contrast of any alexandrite colour change — rather than the specific Minas Gerais locality. Laboratory reports for fine alexandrite generally identify species and treatment without rendering an intra-Brazilian geographic origin opinion.