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cat's-eye
varies from pale blue and pale green to reddish-brown. A blue variety
occurring with the South African tiger-eye is known as " hawk's-eye." A
piece of either of these minerals if cut en cabochon in a
proper manner exhibits a band of light across it, changing in position
when the stone is turned. The included fibrous mineral which gives the
effect is asbestos. In the tiger-eye obtained from South Africa all
gradations are found between crocidolite, which is a fibrous form of
amphibole, and quartz, the tiger-eye being formed by a replacement of
the crocidolite by the quartz. Thus the structure of the crocidolite is retained, but the stone has the hardness and luster of quartz.
Cat's-eye
comes chiefly from Asia, the Malabar Coast of India and the Island of
Ceylon being the localities most prolific in it. In the latter locality
it accompanies the Oriental or chrysoberyl cat's-eye. It is, however,
much less valuable than the latter.
Nearly
all the tiger-eye used at the present time comes from South Africa. It
is found in a range of quartzose schists called the Asbestos Mountains,
located in Griqualand, and extending from Griquatown in a northeasterly
direction toward the Transvaal. Griquatown is about one hundred miles
west of Kimberley. Other localities northward along the Orange River
also furnish tiger-eye. The mineral as found varies in color from blue
to yellow, according to the degree of oxidation of the iron of the
mineral. As already noted, the blue is called hawk's-eye. Owing to the
quantity of the raw material available tiger-eye brings a low price,
and has dropped out of fashion to a considerable extent. Twenty-five
years ago it commanded a price of $6 a carat, being rated as high as
turquois at the present day. Owing to the competition of two dealers at
that time and the appearance of an immense supply, the price quickly
fell to less than twenty-five cents per pound, and the demand for it
almost ceased.^
The
cutting of tiger-eye is now largely carried on in Oberstein and
vicinity at the great agate-cutting establishments. Ring and brooch
stones, dishes, and vases are some of the objects made from it.
Aventurine. Quartz
known by this name contains inclusions, not in the form of fibers, but
in that of scales of some bright mineral, such as mica or hematite. The
quartz thus presents a spangled appearance. The spangles, according to
the "size of the included scales, may be coarse or fine. The choicest
aventurine is that in which each scale gives a distinct reflection. The
quartz base may be brown, red, yellow, or black, or rarely bluish or
greenish in color, and the spangles usually silvery or golden. The
aventurine most commonly used is of a reddish yellow color with a
coppery sheen. Aventurine quartz resembles the
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