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.