Chrysocolla

Chrysocolla
Chrysocolla and malachite from Australia
General
Category	Silicate mineral
Formula (repeating unit)	Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (x<1)
Strunz classification	09.ED.20
Unit cell	a = 5.7 Å, b = 8.9 Å, c = 6.7 Å
Identification
Color	Blue, cyan or 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 phyllosilicate mineral with formula: Cu_2-xAl_x(H_2-xSi₂O₅)(OH)₄·nH₂O (x<1) or (Cu,Al)₂H₂Si₂O₅(OH)₄·nH₂O. The structure of the mineral has been questioned, as spectrographic studies suggest material identified as chrysocolla may be a mixture of the copper hydroxide spertiniite and chalcedony.

Properties

Powder-blue chrysocolla as stalactitic growths and as a thin carpet in vugs inside a boulder of nearly solid tyrolite from the San Simon Mine, Iquique Province, Chile (size: 14.1 x 8.0 x 7.8 cm)

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

Name and discovery

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

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

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 Bacan Island Indonesia, Israel, Democratic Republic of Congo, Chile, Cornwall in England, and Arizona, Utah, Idaho, New Mexico, Michigan, and Pennsylvania in the United States.

Questions regarding mineral status

A 2006 study has produced evidence that chrysocolla may be a microscopic mixture of the copper hydroxide mineral spertiniite, amorphous silica and water.

See also

• Chrysocolla (gold-solder)