the last quarter of a century a great deal of this mineral has been
brought from South Africa, and introduced into commerce as Cat's Eye ;
but whilst the true Oriental Cat's Eye is a valuable and beautiful gem,
this stone is comparatively worthless for jewellery. It is, in fact,
mainly a ferruginous Quartz, or Chalcedony, associated with a fibrous
mineral known as true Crocidolite, or a pseudomorph after it.
is a mineral belonging to the group of Hornblendes, and consists of
thin delicate silken fibres compacted together in masses, and often
associated with magnetite or magnetic oxide of iron.
When Crocidolite is cut en cabochon, it
exhibits, in some degree, the Cat's Eye effect ; it being an optical
property of all acicular or fibrous minerals, when cut with a curved
surface, to show more or less chatoyancy on a line at right angles to
the fibres of the substance.
colours of the Crocidolite are usually some shade of yellow, with a ray
of a lighter colour ; or rich brown deepening to almost black ; or a
dark indigo with a zone of lighter blue. The brown variety is known as Tiger's Eye and the blue as Hawk's Eye.
The so-called Crocidolite Cat's Eye comes principally from a locality on the Orange River in Griqualand West,