Montebrasite Locality: Linópolis, Divino das Laranjeiras , Doce valley, Minas Gerais , Southeast Region, Brazil ( Locality at mindat.org ) Size: 9.6 x 9.3 x 6.9 cm. This is a fist-sized cluster of thick, fat, intensely yellow montebrasite crystals with minor cleavelandite association. Clusters are very rare, and these chunky, deep-colored crystals really combine to make a fine overall specimen. The piece is not pristine, as it has some contacts around the edges and a few trivial dings on the display face as well. In person, this material from a modern find at this old locale has a rich color, almost an inside glow to it, that is hard to convey in photos. Weighs 577 grams. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Montebrasite
The hydroxyl-dominant end of the amblygonite series — a lithium-aluminium fluorophosphate of pegmatites.
Intro adapted from Wikipedia (CC BY-SA).
Montebrasite is an IMA-recognized mineral species in the phosphate class, with the chemical formula LiAl(PO₄)(OH).
It crystallizes in the triclinic crystal system (space group C-1). It is a member of the Titanite-Amblygonite structural group.
Key properties: Mohs hardness 5.5–6; specific gravity 2.98–3.04; Vitreous, pearly on cleavages luster; optically biaxial.
IMA symbol Mbs, grandfathered status — known before the IMA’s founding, named in 1871.
A late primary and secondary mineral in zoned granite pegmatites; may be an ore of lithium.
It is found associated with Hydroxylapatite, spodumene, lepidolite, petalite, pollucite, tourmaline, triplite, lithiophilite, lacroixite, crandallite, muscovite, albite.
The name is derived from the locality, Montebras, France, from which it was first described.