The Guide to Rocks and Minerals

In focus: Chrysocolla

Chemical Composition: (Cu,Al)2H2Si2O5(OH)4
Group: Silicate
Colour: Green, Bluish green, Blue, Blackish blue, Brown
Streak: light green
Hardness: 2.5-3.5
Density: 2 - 2.4
Luster: Vitreous
Cleavage: None
Acid sensitive: yes

Chrysocolla is a basic copper silicate made up of approximately 45% copper oxide (CuO) and 34% silica (SiO₂). Chrycolla has a secondary origin, which means it is a metamorphic rock one of those rocks which has changed its composition as a gesult of geological activity. Chrysocolla is typically found as glassy botryoidal (a shape which resembles a bunch of grapes) or as rounded masses. The name is very old, being first used in 315 B.C. by Theophrastus, a student of Aristotle. It is derived from the Greek chrysos, meaning "gold," and kolla, meaning "glue," in allusion to the name of the material used to solder gold.

Chrysocolla has a distinctive light blue-green colour which resembles turquoise, although turquoise is a much harder mineral (hardness 6). True chrysocolla, free of quartz, is fragile and likely to crack as it loses water in dry cabinet environments. Chrysocolla-impregnated chalcedony, which has the quartz hardness of 7, is used in jewelry and as ornamental stones.

Chrysocolla can be found in association with other copper minerals. The main sources are Israel, the Democratic Republic of Congo, Chile, Cornwall in England, and Arizona, Utah, New Mexico and Pennsylvania in the United States.

Mineral uses

jewelry
ornamental stones
collector's items
minor copper ore

Identification

characteristic indicators of chrysocolla are the lack of a crystalline structure, blue-green colour, low density and softness
It is soluble in hydrochloric acid (HCl) with characteristic separation of silica.
Breaks violently if held in flame.
When immersed in water, it takes up a lot of it and crumbles. Never try washing your specimen.
For less scientific identification, when touched by tongue, the tongue clings to the specimen.

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