Augelite

Augelite is an aluminium phosphate mineral with formula: Al₂(PO₄)(OH)₃. The shade varies from colorless to white, yellow or rose. Its crystal system is monoclinic.^[4]

Augelite
General
Category	Phosphate mineral
Formula	Al2(PO4)(OH)3
IMA symbol	Aul[1]
Strunz classification	8.BE.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a = 13.124(6), b = 7.988(5) c = 5.0633(3) [Å] β = 112.25(2)°; Z = 4
Identification
Color	Colorless to white, may be yellowish to pale rose, greenish
Crystal habit	Tabular to prismatic or acicular crystals; massive
Cleavage	Perfect on {110}, good on {201}, imperfect on {001} and {101}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	4 – 4.5
Luster	Vitreous, pearly on {110} cleavage
Streak	White
Diaphaneity	Transparent
Specific gravity	2.696
Optical properties	Biaxial (+)
Refractive index	nα = 1.574 nβ = 1.576 nγ = 1.588
Birefringence	δ = 0.014
2V angle	Measured: 50°
References	[2][3]

It was first described by Christian Wilhelm Blomstrand for an occurrence in Västanå iron mine at Scania, Sweden in 1868 and derives its name from the Greek αύγή in reference to its pearly lustre.^[2][3]

It occurs as a product of metamorphism of phosphate bearing peraluminous sediments and in high-temperature hydrothermal ore deposits. It occurs in association with attakolite, svanbergite, lazulite, hematite, trolleite, berlinite, rutile, pyrophyllite, baryte, arsenopyrite, stannite, pyrite, andorite, cassiterite and zinkenite.^[2]