Chrysocolla

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Chrysocolla
Chrysocolla.jpg
Chrysocolla and malachite from Australia
General
Category Silicate mineral
Formula
(repeating unit)
Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (x<1)[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 [2][1][3]

Chrysocolla is a hydrated copper cyclosilicate mineral with formula: Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (x<1)[1] or (Cu,Al)2H2Si2O5(OH)4·nH2O.[2] 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[edit]

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[edit]

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[edit]

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 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[edit]

A 2006 study has produced evidence that chrysocolla may be a microscopic mixture of the copper hydroxide mineral spertiniite, amorphous silica and water.[4][1]

References[edit]