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Category Phosphate minerals
(repeating unit)
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
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 [1][2][3]

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.[3] It occurs associated with apatite, whitlockite, childreniteeosphorite, laueite, strunzite, stewartite, mitridatite, amblygonite and siderite.[2]

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.[1]