Cacoxenite

Cacoxenite
240px Cacoxenite, Minas de Horcajo, Castile-La Mancha, Spain
General
Category	Phosphate minerals
Formula (repeating unit)	Fe3+24Al(PO4)17O6(OH)12·17(H2O)
Strunz classification	08.DC.40
Crystal symmetry	Hexagonal dipyramidal H-M symbol: 6/m Space group: P63/m
Unit cell	a = 27.559(1) Å, c = 10.55Å; Z = 2
Identification
Color	Yellow to brownish yellow, reddish orange, golden yellow, deep orange, green; yellow in transmitted light
Crystal habit	Acicular, radial, stellate
Crystal system	Hexagonal
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

Cacoxenite is an iron aluminium phosphate mineral with formula: Fe³⁺₂₄Al(PO₄)₁₇O₆(OH)₁₂·17(H₂O). 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. It occurs as a secondary phase in oxidized magnetite and limonite deposits. It also occurs in novaculites and in iron and phosphorus rich sediments.

References

File:Cacoxenite-40667.jpg

Cacoxenite, 6.2 x 5.4 x 4.1 cm, Fort Lismeenagh, Shanagolden, County Limerick, Ireland

File:Quartz-cacoxenite.jpg

Quartz with cacoxenite - cut - Minas Gerais - Brasil