Wavellite

Wavellite
Wavellite cluster from Saline County, Arkansas (size: 4.5 x 4.2 x 3.6 cm)
General
Category	Phosphate minerals
Formula (repeating unit)	Al3(PO4)2(OH,F)3·5H2O
Strunz classification	8.DC.50
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pcmn
Unit cell	a = 9.621 Å b = 17.363 Å, c = 6.994 Å; Z = 4
Identification
Color	Green to yellowish-green and yellow, brown, white and colorless
Crystal habit	Spherical, radial aggregates; striated prisms; crusty to stalactitic
Cleavage	[110] perfect, [101] good, [010] distinct
Fracture	Uneven to subconchoidal
Mohs scale hardness	3.5 - 4
Luster	Vitreous to resinous, pearly
Streak	White
Diaphaneity	Translucent
Specific gravity	2.36
Optical properties	Biaxial (+)
Refractive index	nα = 1.518 - 1.535 nβ = 1.524 - 1.543 nγ = 1.544 - 1.561
Birefringence	δ = 0.026
Pleochroism	Weak; X = greenish; Z = yellowish
2V angle	Measured: 60° to 72°
Fusibility	Infusable, swells and splits on heating
Solubility	Insoluble
References

Wavellite is a phosphate mineral with formula Al₃(PO₄)₂(OH, F)₃·5H₂O. It normally occurs as translucent green radial or spherical clusters.

It was first described in 1805 for an occurrence within the High Down Quarry, Filleigh, Devon, England and named for William Wavell (20 December 1750 - 15 January 1829) of England who discovered the mineral.

It occurs in association with crandallite and variscite in fractures in aluminous metamorphic rock, in hydrothermal regions and in phosphate rock deposits. It is found in a wide variety of locations notably in the Mount Ida, Arkansas area in the Ouachita Mountains.

It is sometimes used as a gemstone.