| Chrysocolla | |
|---|---|
 Chrysocolla specimen fromRay mine, in theScott Mountain area of Mineral Creek District,Pinal County, Arizona, US | |
| General | |
| Category | Phyllosilicateminerals |
| Formula | Cu2 −xAlx(H2Si2O5)(OH)4·nH2O (x < 1)[1] |
| IMA symbol | Ccl[2] |
| Strunz classification | 9.ED.20 |
| Crystal system | Orthorhombic Unknown space group |
| Unit cell | a = 5.7 Å, b = 8.9 Å, c = 6.7 Å; Z = 1 |
| Identification | |
| Color | Blue,cyan (blue-green), green, dark blue to black, brown, rarely yellow |
| Crystal habit | Massive, nodular,botryoidal |
| Cleavage | none |
| Fracture | Irregular/uneven, sub-conchoidal |
| Tenacity | Brittle tosectile |
| Mohs scale hardness | 2.5–3.5 (7 for chrysocolla chalcedony, high-silica content) |
| 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 | [3][4][1][5] |
Chrysocolla (/ˌkrɪsəˈkɒlə/KRIS-ə-KOL-ə) is ahydrouscopperphyllosilicatemineral andmineraloid with theformulaCu
2 –xAl
x(H
2Si
2O
5)(OH)
4⋅nH
2O (x < 1)[1] or(Cu, Al)
2H
2Si
2O
5(OH)
4⋅nH
2O).[4]
The structure of the mineral has been questioned, as a 2006 spectrographic study suggest material identified as chrysocolla may be a mixture of the copper hydroxidespertiniite andchalcedony.[6]
Chrysocolla typically forms amorphously.[7]
The namechrysocolla comes from theAncient Greekχρυσός (khrusós) andκολλα (kolla), meaning "gold" and "glue" respectively,[8] in allusion to the name of the material used tosoldergold. The word was first used byTheophrastus in 315 BC.
Chrysocolla has acyan (blue-green) color and is a minor ore of copper, having ahardness of 2.5 to 7.0. It is of secondary origin and forms in theoxidation zones of copperore bodies. Associated minerals arequartz,limonite,azurite,malachite,cuprite, and other secondary copper minerals. It is typically found asbotryoidal or rounded masses and crusts, or vein fillings.
A 2006 study has produced evidence that chrysocolla may be a microscopic mixture of the copper hydroxide mineralspertiniite, amorphous silica and water.[6][1]
Due to being somewhat more common thanturquoise, its wide availability, and vivid, beautiful blue and blue-green colors, chrysocolla has been popular for use as a gemstone for carvings and ornamental use since antiquity. It is often used insilversmithing andgoldsmithing in place of turquoise and is relatively easy to work and shape. Chrysocolla exhibits a wide range ofMohs hardness ranging from 2 through 7, which is dependent on the amount of silica incorporated into the stone when it is forming. Generally, dark navy blue chrysocolla is too soft to be used in jewelry, while cyan, green, and blue-green chrysocolla can have a hardness approaching 6, similar to turquoise. Chrysocolla chalcedony is a heavily silicified form of chrysocolla that forms in quartz deposits and can be very hard and approach a hardness of 7.[9][10][11]
