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 in length and 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 brazilianite specimens found in mineral collections originated from the Palermo and the Charles Davis mines in Grafton County, New Hampshire.
Composition
Brazilianite, NaAl<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub> is a hydrous sodium aluminium phosphate that forms through the metasomatic alteration of amblygonite-montebrasite. Amblygonite, LiAlPO<sub>4</sub>F in combination with quartz goes through an OH-F exchange to make montebrasite, LiAlPO<sub>4</sub>{F,OH} at temperatures greater than 480 °C. 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. The Al-octahedra has two types of octahedral coordination: trans-AlO<sub>4</sub>(OH)<sub>2</sub> and trans-AlO<sub>3</sub>(OH)<sub>3</sub>. The two phosphorus atoms in brazilianite are coordinated in a tetrahedral with four oxygen atoms each. Most common forms that are measured in brazilianite {010}, {110}, { 11}. It displays a perfect cleavage on (010), it is brittle and has a conchoidal fracture. Brazilianite also found with tourmaline and feldspar.
Brazilianite is relatively new phosphate minerals along with amblygonite, turquoise and apatite that are used as gemstones. Even though it was first described in 1945, its discovery was actually in 1944 but it was believed it was chrysoberyl until analysis was done to the mineral indicating a new mineral. It is soft and fragile causing it not to be a popular stone.