Allanpringite

Allanpringite is a phosphate mineral that was named after the Australian mineralogist, Allan Pring of the South Australian Museum.

Allanpringite
Picture width 4 mm
General
Category	Phosphate mineral
Formula	Fe3+3(PO4)2(OH)3·5H2O
IMA symbol	Apg[1]
Strunz classification	8.DC.50
Dana classification	42.10.02.02
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/n
Unit cell	a = 9.777, b = 7.358 c = 17.83 [Å]; β = 92.19°; Z = 4
Identification
Formula mass	498.07 g/mol
Color	Pale brownish yellow
Crystal habit	Acicular
Cleavage	{hk0} perfect, {010} good
Fracture	Irregular/uneven
Tenacity	Brittle
Mohs scale hardness	3
Luster	Vitreous
Streak	Pale yellowish white
Diaphaneity	Translucent to transparent
Specific gravity	2.54 (meas.), 2.583 (calc.)
Optical properties	Biaxial (+)
Refractive index	nα = 1.662 nβ = 1.675 nγ = 1.747
Birefringence	0.085
2V angle	48° (calc.)
References	[2][3]

Allanpringite is a Fe³⁺ analogue Al-phosphate mineral wavellite, but it has a different crystal symmetry – monoclinic instead of orthorhombic in wavellite.

It forms needle-like crystals, which are always twinned and form parallel bundles up to about 2 mm long. They are often found in association with other iron phosphates in abandoned iron mines.^[2][4]