Before
the blowpipe it becomes darker, but is infusible, except in the case of
the variety called hyalosiderite, which melts into a black magnetic
globule. This stone, as its name implies, contains a large quantity of
iron. All the varieties give the iron and silica reactions, and are
easily and completely dissolved by sulphuric acid into a jelly.
This
stone is called peridot when of a deep olive-green, olivine when of a
yellowish-green, and chrysolite when of a lighter, or of a
greenish-yellow, colour. Mineralogists enumerate many other varieties,
but they are of little interest, except to the mineralogical student.
Peridots are found in Ceylon, Pegu, Brazil, and also near
Constantinople, in angular or worn pieces, very rarely crystallized ;
they are not, however, very plentiful. The olivine and chrysolite
occur in Egypt, Mexico, in Auvergne, the Tyrol, Scotland, etc., usually
in substances of volcanic origin. Specimens have been met with in the
lava of Vesuvius.
None
of the varieties of this gem are much used in jewellery, although some
of them possess a very beautiful deep colour ; perhaps the fact of its
being scratched very easily may be the cause. They are usually cut in
steps, or en cabochon. On the Continent the chrysolite is often cut like a rose diamond, and set with a gold foil :
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