PRECIOUS STONES. 227
known
as Tiger's Eye is produced ; it may also be regarded as a form of
Quartz containing pseudomorphs of Crocidolite in Limonite. The Hawk's
Eye may thus show a transition to Tiger's Eye; hence the only definite
starting point we have in tracing the origin of these two precious
stones is the original Crocidolite, and for this reason they are
described under this species. It follows, from what has been said, that
when the infiltration by Quartz is complete the specific gravity is
that of Quartz with a slight excess due to the inclusions, and further
the hardness is 7.
Tiger's
Eye and Hawk's Eye both occur in veins in schists in the Asbestos
Mountains in Griqualand West, and in other parts of South Africa.
At
one time the material was scarce and was only used for smaller articles
of ornament, but now there is a plentiful supply and the price has
fallen so much that it is commonly used for paper weights, umbrella
handles, and other similar articles. The variety Tiger's Eye when
polished with the exposed surface parallel to the fibres had a
particularly brilliant golden brown colour and shows a highly silky
lustre.
