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Brazilianite
Brazilianite, whose name derives from its country of origin, Brazil, is a typically yellow-green phosphate mineral, most commonly found in phosphate-rich pegmatites.
It occurs in the form of perfect crystals grouped in druses, in pegmatites, and is often of precious-stone quality. One noted deposit of brazilianite is in the surroundings of Conselheiro Pena, in Minas Gerais, Brazil.
Some of these are found on leaves of muscovite with their strong silvery glitter, ingrown in their parent rock. The crystals, dark greenish-yellow to olive-green, sometimes measure up to 12 cm in length and 8 cm in width. Crystals of similar shape and dimensions have been discovered in another deposit in Minas Gerais, near Mantena, but they lack the perfection of the crystal form. Many brazilianites found in mineral collections originated from the Palermo and the Charles Davis mines in Grafton County, New Hampshire.
== Composition ==
Brazilianite, NaAl3(PO4)2(OH)4 is a hydrous sodium aluminium phosphate that forms through the metasomantic alteration of amblygonite-montebrasite. Amblygonite, LiAlPO4F in combination with quartz goes through an OH-F exchange to make montebrasite, LiAlPO4 at temperatures greater than 480 °C.〔 Natromontebrasite, NaAl(PO4)(OH), is formed when montebrasite does though Li-leaching process and there is a Na cation exchange at temperatures less than 450 °C.〔 Brazilianite concludes this process by forming as natromontebrasite combines with fluorapatite, Ca5(PO4)3F. Due to its formation caused by the amblygonite-montebrasite alteration and the presence of tourmaline in the environment where brazilianite forms, different elements are present in the mineral such as P, Al, Fe, Mn, Ba, Sr, Ca, Mg, Na, K, F, and Cl. There are many substitution possibilities in the brazilianite formula. Besides sodium, being replaced by any other element, iron can replace aluminium and vanadates or arsenates can replace the phosphates.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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