Berlinite

Berlinite
Synthetic berlinite
General
Category	Phosphate mineral
Formula (repeating unit)	AlPO4
Strunz classification	08.AA.05
Crystal system	Trigonal
Space group	Trigonal trapezohedral H-M symbol: 32 Space group: P3121
Unit cell	a = 4.941 Å, c = 10.94 Å; Z = 3
Identification
Color	Colorless, pale gray, may be pale rose
Crystal habit	Typically granular to massive
Twinning	Subparallel lamellae
Fracture	Conchoidal
Mohs scale hardness	6.5
Luster	Vitreous
Diaphaneity	Transparent to translucent
Specific gravity	2.64–2.66
Optical properties	Uniaxial (+)
Refractive index	nω = 1.524 nε = 1.532
Birefringence	δ = 0.008
References

Berlinite (aluminium phosphate, chemical formula AlPO₄) is a rare phosphate mineral. It has the same crystal structure as quartz with a low temperature polytype isostructural with α–quartz and a high temperature polytype isostructural with β–quartz. Berlinite can vary from colourless to greyish or pale pink and has translucent crystals.

It was first described in 1868 for an occurrence in the Västanå iron mine, Scania, Sweden and named for Nils Johan Berlin (1812–1891) of Lund University.

It occurs as a rare mineral in high-temperature hydrothermal or metasomatic deposits. Associated minerals include augelite, attakolite, kyanite, pyrophyllite, scorzalite, lazulite, gatumbaite, burangaite, amblygonite, phosphosiderite, purpurite, apatite, muscovite, quartz, hematite in granite pegmatites. It also occurs with alunite, aragonite, collophane, crandallite, francoanellite, gypsum, huntite, hydromagnesite, leucophosphite, nesquehonite, niter, and nitrocalcite in the Paddy’s River copper mine in the Brindabella Mountains of Australia.

Further reading

• Muraoka, Y.; Kihara, K. (1997). "The temperature dependence of the crystal structure of berlinite, a quartz-type form of AlPO₄". Physics and Chemistry of Minerals. 24 (4): 243. Bibcode:1997PCM....24..243M. doi:10.1007/s002690050036.