Chrysocolla

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Chrysocolla
Chrysocolla.jpg
Chrysocolla and malachite from Australia
General
CategorySilicate mineral
Formula
(repeating unit)
Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (x<1)[1]
Strunz classification09.ED.20
Unit cella = 5.7 Å, b = 8.9 Å, c = 6.7 Å
Identification
ColorBlue, cyan or blue-green, green
Crystal habitMassive, nodular, botryoidal
Crystal systemOrthorhombic
Cleavagenone
FractureIrregular/uneven, sub-conchoidal
TenacityBrittle to sectile
Mohs scale hardness2.5 - 3.5
LusterVitreous to dull
Streakwhite to a blue-green color
DiaphaneityTranslucent to opaque
Specific gravity1.9 - 2.4
Optical propertiesBiaxial (-)
Refractive indexnα = 1.575 - 1.585 nβ = 1.597 nγ = 1.598 - 1.635
Birefringenceδ = 0.023 - 0.050
References[2][1][3]
 
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Chrysocolla
Chrysocolla.jpg
Chrysocolla and malachite from Australia
General
CategorySilicate mineral
Formula
(repeating unit)
Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (x<1)[1]
Strunz classification09.ED.20
Unit cella = 5.7 Å, b = 8.9 Å, c = 6.7 Å
Identification
ColorBlue, cyan or blue-green, green
Crystal habitMassive, nodular, botryoidal
Crystal systemOrthorhombic
Cleavagenone
FractureIrregular/uneven, sub-conchoidal
TenacityBrittle to sectile
Mohs scale hardness2.5 - 3.5
LusterVitreous to dull
Streakwhite to a blue-green color
DiaphaneityTranslucent to opaque
Specific gravity1.9 - 2.4
Optical propertiesBiaxial (-)
Refractive indexnα = 1.575 - 1.585 nβ = 1.597 nγ = 1.598 - 1.635
Birefringenceδ = 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]