Svanbergite

Svanbergite is a colorless, yellow or reddish mineral with the chemical formula SrAl₃(PO₄)(SO₄)(OH)₆. It has rhombohedral crystals.[3]

Svanbergite
Svanbergite with pyrophyllite and andalusite
General
Category	Phosphate minerals
Formula (repeating unit)	SrAl3(PO4)(SO4)(OH)6
Strunz classification	8.BL.05
Crystal system	Trigonal
Crystal class	Hexagonal scalenohedral (3m) H-M symbol: (3 2/m)
Space group	R3m
Unit cell	a = 6.970–6.992 Å c = 16.567–16.75 Å, Z = 3
Identification
Color	Colorless, cream-yellow, rose, reddish brown
Crystal habit	Rhombohedral crystals (to pseudocubic); granular, massive
Cleavage	Distinct on {0001}
Mohs scale hardness	5
Luster	Vitreous to adamantine
Diaphaneity	Translucent
Specific gravity	3.22
Optical properties	Uniaxial (+)
Refractive index	nω = 1.631–1.635 nε= 1.646–1.649
Birefringence	δ=0.0140-0.0150
References	[1][2]

It was first described for an occurrence in Varmland, Sweden in 1854 and named for Swedish chemist Lars Fredrik Svanberg (1805–1878).[1][2]

It occurs in high aluminium medium-grade metamorphic rocks; in bauxite deposits and from sulfate enriched argillic alteration ( high silica and clay) associated with hydrothermal systems often replacing apatite. It occurs with pyrophyllite, kyanite, andalusite, lazulite, augelite, alunite, kaolinite and quartz.[1]

Svanbergite crystals on white dolomite from Radium Hot Springs, British Columbia, Canada (size: 3 x 2.5 x 2.1 cm)