Brazilianite

Brazilianite
Brazilianite from type locality, Conselheiro Pena, Minas Gerais, Brazil
General
Category	Phosphate minerals
Formula (repeating unit)	NaAl3(PO4)2(OH)4 sodium aluminium phosphate hydroxide
IMA symbol	Bzl[1]
Strunz classification	8.BK.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/n
Unit cell	a = 11.229 Å, b = 10.142 Å, c = 7.098 Å; β = 97.4°; Z = 4
Identification
Color	Yellow, green, colorless
Crystal habit	Prismatic crystals, may be radially-fibrous or globular druses
Cleavage	(010) Distinct to good
Fracture	Conchoidal
Mohs scale hardness	5.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.98
Optical properties	Biaxial (+)
Refractive index	nα = 1.602 nβ = 1.609 nγ = 1.621 - 1.623
Birefringence	δ = 0.019 - 0.021
References	[2][3]

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 (4.7 in) in length and 8 cm (3.1 in) 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.^{[citation needed]} Many brazilianite specimens found in mineral collections originated from the Palermo and the Charles Davis mines in Grafton County, New Hampshire.