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Montebrasite is a lithium aluminophosphate, which is formed in pegmatites enriched in lithium (Li). It forms a series with amblygonite ((Li,Na)AlPO4F), which is a lithio-sodic equivalent. It is not easy to distinguish them one from the other, it is necessary for that to perform lithium analyses.
It was exploited in Montebras in Soumans, Creuse (from where it got its name) for lithia (LiOH, lithium hydroxide).
The morphology of montebrasite is rather difficult to describe and although certain crystals are prismatic, the majority of them are complex in shape. The crystals are of pale colour: colourless with yellowish, gray, pink-purple but always pale.
This phosphate does not have a very high hardness; it is easily cut and takes a beautiful polish. The gem collectors appreciate this cut gem because the specimens are rather rare.
Many samples are indifferently named "amblygonite". The largest current world deposits are in Brazil: the parts are gemmeous and present up to the centimetre in size. As for the French deposits: Montebras, Boussac (Creuse) and the quarry of Beauvoir, Echassières (Allier). The French montebrasites discovered so far are white with yellow, opaque even translucent, but are not gemmeous.
The type of this species is kept at the National Natural history museum of Natural History of Paris. It was studied by Des Cloizeaux in 1872, on a sample of Montebras in Soumans.
HISTORY : Named to recall its type-locality: Montebras, Creuse, France
Species first described in 1871 by Alfred Descloizeaux (1817-1897), French mineralogist and cristallographer
Type-locality : Mine Montebras, Creuse, France
CHEMICAL FORMULA : LiAlPO4OH
CRYSTAL SYSTEM : Triclinic
COLOR : Colorless, white, yellow pale, pale pinky-violett
DIAPHANIETY : Translucent to transparent
LUSTER : Vitreous to pearly
STREAK : White
MORPHOLOGIE : Prismatic crystals, isometric, massive
HARDNESS : 5,5-6,0
CHEMICAL CLASS: 3,03
DENSITY : VII - Phosphates, arsenates and vanadates
GROUP : Amblygonite
STRUNZ CLASS BEFORE 2001 : 7/B.02-40
STRUNZ CLASS AFTER 2001 : 8.BB.05
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