Cacoxenite

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.

Cacoxenite
Cacoxenite, Minas de Horcajo, Castile-La Mancha, Spain
General
CategoryPhosphate minerals
Formula
(repeating unit)
Fe3+24Al(PO4)17O6(OH)12·17(H2O)
Strunz classification8.DC.40
Crystal systemHexagonal
Crystal classDipyramidal (6/m)
(same H-M symbol)
Space groupP63/m
Unit cella = 27.559(1) Å,
c = 10.55 Å; Z = 2
Identification
ColorYellow to brownish yellow, reddish orange, golden yellow, deep orange, green; yellow in transmitted light
Crystal habitAcicular, radial, stellate
CleavageNone
FractureUneven
Mohs scale hardness3-4
LusterSilky
StreakWhite
Diaphaneitysemitransparent
Specific gravity2.2 - 2.6
Optical propertiesUniaxial (+)
Refractive indexnω = 1.575 - 1.585 nε = 1.635 - 1.656
Birefringenceδ = 0.060
Pleochroismvisible: O = Pale yellow E = Canary yellow to yellow orange
References[1][2][3]

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

References

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