Anhydrous phosphate containing hydroxyl, amblygonite group, and forms a series with it
Specific gravity: 2.98 to 3.04
Hardness: 5½ to 6
Colour: White, colourless, gray white, very pale brown, pale pink, pale yellow
Solubility: Soluble with difficulty in acids. Colours a flame red (Mindat)
Common impurities: Na
Montebrasite is a late primary and secondary phosphate in
granite pegmatites, often forming very large crystals up to one metre in length.
Associated minerals include hydroxylapatite,
albite (HOM, Dana, Mindat).
At the type locality, the Montebras Mines, Creuse, Nouvelle-Aquitaine, France, montebrasite occurs in a granite pegmatite (Mindat).
At the Karibib district, Namibia, montebrasite occurs in lepidolite pegmatite with petalite (Dana).
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, montebrasite occurs as pods to 25 cm across in the core margin. In many cases the pods are associated with triphylite-lithiophilite or with pollucite and beryl. One mass has been found which is an intergrowth of montebrasite with barium-bearing goyazite. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.511-512).
Montebrasite may alter to mixtures of clay minerals or kaolinite and mica, often as rims surrounding rounded nodules of unaltered material. It is also observed to alter to turquoise, wavellite, wardite or morinite (Mindat).
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