Libethenite

Libethenite
Libethenite, Wheal Phoenix, Linkinhorne, Cornwall, England. Size: 5.0 x 4.9 x 2.8 cm.
General
Category	Phosphate minerals
Formula (repeating unit)	Cu2PO4OH
Strunz classification	8.BB.30
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnnm
Identification
Color	Light to dark green, blackish green, olive-green
Crystal habit	Globular, druzy, slender prismatic
Cleavage	Indistinct on [100] and [010]
Fracture	Irregular, uneven to conchoidal
Tenacity	Brittle
Mohs scale hardness	4
Luster	Vitreous, greasy
Streak	light green
Specific gravity	3.6 - 4, Average = 3.8
Optical properties	Biaxial (-)
Refractive index	nα = 1.701 - 1.704 nβ = 1.743 - 1.747 nγ = 1.787 - 1.790
References

Libethenite is a rare copper phosphate hydroxide mineral. It forms striking, dark green orthorhombic crystals. It was discovered in 1823 in Ľubietová, Slovakia and is named after the German name of that locality (Libethen). Libethenite has also been found in the Miguel Vacas Mine, Conceição, Vila Viçosa, Évora District, Portugal, and in Tier des Carrières, Cahai, Vielsaim, Stavelot Massif, Luxembourg Province, Belgium.

Libethenite almost always takes the form of dark-green orthorhombic crystals. It is often found in clusters with other libethenite crystals.

Libethenite is found in the oxidized zone of copper ore deposits. It is most often formed from the weathering of phosphate rocks such as apatite, monazite, and xenotime. There have been no confirmed findings of primary libethenite, although a probable case has been reported.