transparent
and of any colour or colours. Perhaps the commonest of these minerals
is the quartz cat's-eye, which falls far short of rivalling the
brilliancy and soft colouring of cymophane. The shades of this variety
of quartz are greenish, yellowish-grey, and brown. Simple tests will
distinguish this mineral from cymophane, as its hardness is but 6 to 7
and its specific gravity, 2.6. This quartz melts with soda to a clear
glass, is soluble in hydrofluoric acid, and is not dichroic; its chief
components are silicon and oxygen. Cut en caboclwn, a band of light appears across the parallel fibres of asbestos which the quartz contains.
Tiger-eye,
in the trade, is considered separately from cat's-eye, but as
chatoyancy is its chief characteristic, it may as well be included here
and, as its present commercial value is low and the demand for it is
small, it can be summarily described and dismissed. The proper term for
the mineral known as " tiger-eye " is crocidolite, a name derived from
the Greek and meaning " woof," in allusion to its fibrous structure.
Crocidolite is a fibrous asbestoslike mineral. Its colours are
gold-yellow, ranging to yellowish-brown, indigo to greenish-blue,
leek-green and a dull red. The blue is
