Brazilianite

Description

Brazilianite is one of mineralogy rarer phosphates. A hydrous sodium aluminium phosphate (NaAl3PO4-2-OH-4) formally described as a new species in 1945, having been mistaken for chrysoberyl the year prior. The name derives directly from Brazil, the country of its discovery and still the source of the finest specimens known to science. In hand specimen, brazilianite vitreous yellow-green lustre mimics several better-known minerals; under close examination, its monoclinic prismatic habit, perfect cleavage on 010, and characteristic yellow-chartreuse colour are unmistakable.

Linopolis, in the Vale do Rio Doce region of Minas Gerais, is among the most celebrated localities for brazilianite anywhere. The complex lithium-bearing granitic pegmatites of this district produce crystals of exceptional size and transparency – elongated prisms terminated by well-developed faces, frequently showing the bright yellow-to-yellow-green colour that has made the locality famous among collectors worldwide. The geological conditions here – late-stage hydrothermal alteration of phosphate-bearing pegmatite pockets – created exactly the low-temperature, sodium-rich environment in which brazilianite crystallises, typically in association with albite, muscovite, tourmaline and apatite.

With a Mohs hardness of 5.5 and a conchoidal fracture, brazilianite is not among the most robust of collector minerals, which makes intact, well-terminated crystals all the more prized. The vitreous lustre gives cleaved surfaces a bright, gemmy appearance; transparent material has occasionally been faceted for gemological purposes, though collector specimens on matrix remain far more sought after. Crystal system: monoclinic. Density: 2.98 g/cm3. Streak: white.

This specimen was sourced directly during our Brazil expedition to Minas Gerais. It has not been treated with acids or mechanically altered beyond standard field preparation.