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CHRYSOCOLLA
This
mineral in its pure state is too soft to be used as a gem, but mixed
with quartz, or constituting practically a stain, it affords blue and
green stones, resembling turquois on the one hand and chryso-prase on
the other. In fact, it is not unlikely that some of the so-called
turquois obtained in Utah and Nevada is in reality chrysocolla.
Typically chrysocolla is a hydrous silicate of copper, having the
percentages: silica, 34.3, copper oxide, 45.2, and water, 20.5. It thus
resembles dioptase in composition, but unlike that mineral it does not
crystallize. Its hardness varies from 2 to that of quartz if mixed with
that mineral. Its specific gravity is slightly greater than that of
quartz. Its blowpipe reactions do not differ from those of turquois
essentially, because of the content of copper in the latter, but
chrysocolla gives no test for phosphoric acid.
When of good color and hardness chrysocolla affords a stone resembling turquois or chrysoprase.
Chrysocolla
occurring in Nizhni-Tagilsk, in the Urals, is of a sky-blue color, and
is known as demidovite. It has been cut to some extent. In our own
country chrysocolla occurs in numerous copper mines, especially in
Michigan, Arizona, and Nevada, but not much use has yet been made of it
in jewelry.
The
name chrysocolla is from the Greek, and means gold glue. It was so
called from its resemblance to a substance used by the ancients for
soldering gold. It is mentioned by Pliny, and was probably known to the
Romans, though not used for ornamental purposes.
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