Mineralpedia Details for Montebrasite

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Montebrasite

Named for the type locality at Montebras in France. Montebrasite is an uncommon but widespread mineral that occurs as “a late primary and secondary mineral in zoned granite pegmatites.” Montebrasite may locally be an ore of lithium. Well studied material comes from localities in France, Sweden, Canada, in the USA including at several mines here in the Black Hills of South Dakota, Brazil and Rwanda. May fluoresce under long- and short-wave ultraviolet light.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/montebrasite.pdf

Formula: LiAlPO₄(OH)
Crystal System: Triclinic
Crystal Habit: Massive - Granular, Prismatic
Cleavage: Perfect, Good, Distinct
Luster: Vitreous - Greasy
Color: bluish, colorless, greenish, greenish gray, gray white
Streak: white
Class: Triclinic - Pinacoidal
Fracture: Brittle - Conchoidal
Hardness: 5.5-6
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Montebrasite from Telirio mine, Linopolis, Minas Gerais, Brazil

Honey yellow, large, well-formed, striated crystal to 2.5cm.

Honey colored, striated and very lustrous Montebrasite crystal. Crystals of Montebrasite and fairly rare worldwide.

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Montebrasite from Tin Mountain mine, Custer Co., South Dakota, United States

This is a large crystal of Montebrasite, an umcommon lithium phosphate. Lithium phosphates are almost exclusively found in zoned (differentiated) pegmatites. Montebrasite from the Tin Mountain pegmatite occur in huge masses and crude crystals measured in feet or meters. This one is a collectable size and shows crude crystal faces. It is a primary phosphate, which occurs in pegmatites with less iron, otherwise Triphylite would form in the presence of phosphate. Most primary phosphate get attacked by the resulting residual solutions and (perhaps) later hydrothermal solutions in metasomatic reactions. As such, crystal faces of the primary phosphates become rounded or completely absent giving them a more "nodular" appearance. A good reference on these reactions and pegmatitic phosphates can be found in the 1973 May/June issue of the Min. Record authored by the world renowned phosphate expert, Paul Moore.