Chemistry:Cacoxenite

Cacoxenite
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	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
Identification
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
|re|er}}	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). Cacoxenite 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.

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