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Cacoxenite, Minas de Horcajo, Castile-La Mancha, Spain
Category Phosphate minerals
(repeating unit)
Strunz classification 8.DC.40
Crystal system Hexagonal
Crystal class Dipyramidal (6/m)
(same H-M symbol)
Space group P63/m
Unit cell a = 27.559(1) Å,
c = 10.55 Å; Z = 2
Color Yellow to brownish yellow, reddish orange, golden yellow, deep orange, green; yellow in transmitted light
Crystal habit Acicular, radial, stellate
Cleavage None
Fracture Uneven
Mohs scale hardness 3-4
Luster Silky
Streak White
Diaphaneity semitransparent
Specific gravity 2.2 - 2.6
Optical properties Uniaxial (+)
Refractive index nω = 1.575 - 1.585 nε = 1.635 - 1.656
Birefringence δ = 0.060
Pleochroism visible: O = Pale yellow E = Canary yellow to yellow orange
References [1][2][3]

Cacoxenite is an iron aluminium phosphate mineral with formula: Fe3+24Al(PO4)17O6(OH)12·17(H2O).[3] It is associated with iron ores. The name comes from the Greek κăκός for "bad" or "evil" and ξένος for "guest" because the phosphorus content of cacoxenite lessens the quality of iron smelted from ore containing it.

It was first described in 1825 for an occurrence in the Hrbek Mine, Bohemia, Czech Republic.[3] It occurs as a secondary phase in oxidized magnetite and limonite deposits. It also occurs in novaculites and in iron and phosphorus rich sediments.[3]


Cacoxenite, 6.2 x 5.4 x 4.1 cm, Fort Lismeenagh, Shanagolden, County Limerick, Ireland
Quartz with cacoxenite - cut - Minas Gerais - Brasil