Chrysocolla

Chrysocolla
Chrysocolla from Australia
General
Category	Silicate mineral
Chemical formula	(Cu,Al)2H2Si2O5(OH)4·nH2O
Strunz classification	9.ED.20
Unit cell	a = 5.7 Å, b = 8.9 Å, c = 6.7 Å
Identification
Color	Blue, blue-green, green
Crystal habit	Massive, nodular, botryoidal
Crystal system	Orthorhombic
Cleavage	none
Fracture	Irregular/uneven, sub-conchoidal
Tenacity	Brittle to sectile
Mohs scale hardness	2.5 - 3.5
Luster	Vitreous to dull
Streak	white to a blue-green color
Diaphaneity	Translucent to opaque
Specific gravity	1.9 - 2.4
Optical properties	Biaxial (-)
Refractive index	nα = 1.575 - 1.585 nβ = 1.597 nγ = 1.598 - 1.635
Birefringence	δ = 0.023 - 0.050
References

Chrysocolla is a hydrated copper silicate mineral with formula (Cu,Al)₂H₂Si₂O₅(OH)₄·nH₂O.

Properties

Chrysocolla has a blue-green color and is a minor ore of copper, having a hardness of 2.5 to 3.5.

Name and discovery

Banded green chrysocolla from Bisbee, Arizona (size: 12.2 x 5.5 x 5.2 cm)

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.

Formation and occurrence

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.

It is typically found as botryoidal or rounded masses and crusts, or vein fillings. Because of its light color, it is sometimes confused with turquoise.

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

Powder-blue chrysocolla as stalactitic growths and as a thin carpet in vugs inside a boulder of nearly solid tyrolite. Size: 14.1 x 8.0 x 7.8 cm. Locality: San Simon Mine, Santa Rosa-Huantajaya District, Iquique Province, Chile