Xanthoxenite

Xanthoxenite is a rare calcium iron(III) phosphate mineral with formula: Ca₄Fe³⁺₂(PO₄)₄(OH)₂·3H₂O. It occurs as earthy pale to brownish yellow incrustations and lath shaped crystals. It crystallizes in the triclinic crystal system. It occurs as an alteration product of triphylite in pegmatites.^[4] It occurs associated with apatite, whitlockite, childrenite–eosphorite, laueite, strunzite, stewartite, mitridatite, amblygonite and siderite.^[3]

Xanthoxenite
General
Category	Phosphate minerals
Formula	Ca4Fe3+2(PO4)4(OH)2·3H2O
IMA symbol	Xox[1]
Strunz classification	8.DH.40
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 6.7 Å, b = 8.85 Å c = 6.54 Å; α = 92.1° β = 110.1°, γ = 93.2°; Z = 1
Identification
Formula mass	739.95 g/mol
Color	Pale to brownish yellow
Crystal habit	Occurs as platy crystals and as lamellar aggregates and crusts
Cleavage	Perfect {010}
Mohs scale hardness	2.5
Luster	Earthy (dull)
Streak	White
Diaphaneity	Translucent
Specific gravity	2.97 measured, 3.38 calculated
Optical properties	Biaxial (-)
Refractive index	nα = 1.704 nβ = 1.715 nγ = 1.724
References	[2][3][4]

It has been found in Australia, Brazil, Portugal, Spain, Ukraine, and the United States. It was first described in 1920 for an occurrence in North Groton, Grafton County, New Hampshire.^[2]