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Chrysocolla

Chrysocolla
Chrysocolla from Nevada, USA
General
Category	Silicate mineral
Chemical formula	(Cu,Al)₂H₂Si₂O₅(OH)₄·nH₂O
Identification
Color	Blue, blue-green, green
Crystal habit	Massive, nodular, botryoidal
Crystal system	Orthorhombic
Cleavage	none
Fracture	Brittle to sectile
Mohs Scale hardness	2.5 - 3.5
Luster	Vitreous to dull
Refractive index	nω = 1.460 nε = 1.570
Optical Properties	Uniaxial (+)
Birefringence	+0.110
Streak	Light green
Specific gravity	1.9 - 2.4
Diaphaneity	Translucent to opaque

Chrysocolla (hydrated copper silicate) is a mineral, (Cu,Al)₂H₂Si₂O₅(OH)₄·nH₂O. It is of secondary origin and forms in the oxidation zones of copper ore bodies. Associated minerals are quartz, limonite, azurite, malachite, cuprite, and other secondary copper minerals.

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Chrysocolla has an attractive blue-green colour and is a minor ore of copper, having a hardness of 2.5 to 3.5. It is also used as an ornamental stone. It is typically found as glassy botryoidal or rounded masses and crusts, or vein fillings. Because of its light color, it is sometimes confused with turquoise. Commonly it occurs only as pourous crusts unsuitable for gem use, but high quality, gem grade chrysocolla can be translucent and is highly prized.

The name comes from the Greek chrysos, "gold", and kolla, "glue", in allusion to the name of the material used to solder gold, and was first used by Theophrastus in 315 BCE.

Notable occurrences include Israel, Democratic Republic of Congo, Chile, Cornwall in England, and Arizona, Utah, New Mexico and Pennsylvania in the United States.