A Hand-book of Precious StonesRothschild, Meyer D.
Science
A Hand-book of Precious Stones
Rothschild, Meyer D.
Precious stones
These three kinds are usually very brilliant, and especially so by
artificial light, in which respect the beryl is superior to many of the
more valuable gem stones. Beryls of very large size have been found
in New Hampshire, one of which has been estimated to weigh over two
tons. While the large specimens are worthless for gem stones, some very
handsome aquamarines and golden-yellow beryls have been found during
the past few years in New Hampshire and Connecticut. These stones, when
cut, compare favorably with the best of their kind.
CHRYSOBERYL.
The name chrysoberyl is derived from two Greek words signifying
golden-beryl. This name is well suited to the golden-yellow variety,
but the chrysoberyl also includes many other colors: such as green,
greenish-yellow, brownish-yellow, white, and dark-brown to black.
Three varieties of chrysoberyls are known as cat’s-eyes, cymophanes,
and alexandrites.
The chrysoberyl crystallizes in the trimetric or rhombic system; the
cleavage is imperfect; fracture conchoidal; hardness, 8.5, being the
third hardest stone; specific gravity, 3.65 to 3.8; and lustre vitreous
to greasy.
The composition of the chrysoberyl is: alumina, 80.2; glucina, 19.8;
with traces of protoxide of iron and oxides of lead and copper. The
chrysoberyl is doubly refractive to a high degree, acquires positive
electricity lasting several hours, is infusible alone, but melts with
borax or salts of phosphorus to a clear glass, though with difficulty.
The chrysoberyl is unaffected by acids, but with a solution of cobalt
nitrate the powdered mineral becomes blue.
Transparent greenish-yellow chrysoberyls are sometimes called Oriental
chrysolites. These, and the brownish-yellow stones are the gems most
used in jewelry.
The chrysoberyl cat’s-eye, or Ceylon cat’s-eye, is found in various
shadings of yellow, brown, and green, and sometimes nearly black. These
stones are translucent to opaque, and have a bright band of light
running through the centre. This band is nearly always white, and in
fine specimens is sharply defined, not too wide, and is in the centre
of the stone.
The cat’s-eye chrysoberyls are always cut convex or cabochon shape, and
as the stone is moved from side to side the band of light moves over
its surface.
CYMOPHANE.
The cymophane, or floating light, as the name denotes, is a chrysoberyl
with a bright spot of light which seems to float over the surface as
the stone is moved. The cymophane is also cut cabochon.
ALEXANDRITE.
On the day that the Emperor Alexander of Russia attained his majority
the Ural chrysoberyl, of a dark-green color, was found in the emerald
mines of Takowaja in the Catherine Mountains.
This wonderful stone is emerald-green to dark-green in color, with
often a slight red tint, but by artificial light the green of good
specimens changes to a beautiful columbine-red.
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