Part 10

The second and less valuable division of the beryl family comprises the following colors:

Clear light sky-blue, called by lapidaries aquamarine; very light greenish-blue, known as Siberian aquamarine; and a greenish-yellow variety, called aquamarine chrysolite.

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.

As the colors green and red are the national colors of Russia, and the date of discovery of this stone in Russia occurred on the Emperor’s birthday, the name alexandrite was given to this species of chrysoberyl.

The alexandrite is found in large pieces, but is nearly always flawed and cracked. This is a much-sought-after gem stone, and specimens of from one to five carats command good prices. Up to the present time, however, good alexandrites have been rare, and the demand has always exceeded the supply.

Cat’s-eyes and cymophanes are found in Brazil in alluvial deposits of rivers, and consequently in rolled and rubbed masses.

Chrysoberyls are also found in Russia, Germany, America, Borneo, Pegu, and Moravia.

Chrysolites and topazes are sometimes passed off for chrysoberyls. The chrysolite is, however, lighter and softer, while the topaz becomes electric from heating, and is softer.

Quartz cat’s-eyes, which are mistaken for chrysoberyl or Oriental cat’s-eyes, have a specific gravity of about 2.65, hardness of 6 to 6.5, and are soluble in fluoric acid, besides melting with soda into a clear glass.

They lack the bright, hard polish of the chrysoberyl cat’s-eye, and there should be no difficulty in discovering the difference between the gem and the inferior stone.

ZIRCON.

The zircon, hyacinth, jacinth, or jargoon belong to the tetragonal system of crystallization. The cleavage is imperfect, fracture conchoidal, and specific gravity 4.4 to 4.7, the stone being much heavier than any other gems. Its hardness is 7.5 and lustre vitreous to adamantine, and refraction double to a high degree.

The zircon is phosphorescent when heated; before the blow-pipe it is infusible, but loses its color; and with borax it melts into a transparent glass. Sulphuric acid affects this gem after long maceration.

The composition of the zircon is: zirconia, 66.3; silica, 33.7; with a trace of peroxide of iron.