Quartz Variations: Occidental Amethyst, Water Sapphire, Iris, Adventurine

OCCIDENTAL AMETHYST

The amethyst, whose violet colour varies according to the quantity of oxide of manganese combined with the silica, has all the properties of quartz.

This substance is found in France, Prussia, Hungary, Arabia, Ceylon, Kamtschatka, &c. The environs of Carthagena in Spain furnish the most beautiful specimens of amethyst; and they are the more remarkable that they show a purple reflection vying with that of the oriental amethyst.

Brazil furnishes to commerce at the present day the greater number of amethysts. In that part of the world amethysts attain an enormous size. A block of amethyst, sent from the Brazils to Calcutta, is said to have weighed 98 pounds. Some of the Brazilian specimens are of two colours. The Count de Bournon possessed a cut and polished stone of this kind half violet and half yellow.

The ancients believed that wine, when drunk from an amethyst cup, lost the power of causing intoxication. Accordingly the attributes of Bacchus and Silenus are frequently found engraved upon ancient cups of amethyst.

THE WATER SAPPHIRE.

The water sapphire has nothing in common but the colour with the oriental sapphire; and even its colour--a clear white mixed with sky-blue--exhibits to the most inexperienced eyes a shade completely different from the magnificent velvety blue of the oriental sapphire.

There are water sapphires composed of nearly pure quartz; but those brought from Ceylon are of a much more complex composition. Somewhat more than half their weight is silica; the rest is a combination of alumina, magnesia, oxide of iron, and oxide of manganese. This variety is called dichroite, on account of its curious property of showing two very dissimilar colours when viewed from different sides--a beautiful blue in the direction of the axis, and a yellow gray in a direction perpendicular to this line.

IRIS.

Although this stone is no longer mounted by jewellers, and is only seen in antique jewels, it must not be passed over in silence; both because it was held at one time in high repute, and because it is liable to be confounded with several precious stones, particularly the opal.

The iris is a very limpid and very transparent quartz. It is crystallized, a fact which immediately distinguishes it from the opal.

Under the influence of the light the iris is illumined with all the tints of the rainbow. This effect is produced by a great number of flaws and natural crevices contained in its interior; but its fires are always much less close than those of the opal.

Notwithstanding the neglect into which it has fallen, the iris was once very highly thought of. Much was said in the time of the First Empire of a certain parure of iris sometimes worn by the Empress Josephine. It is described among regal jewels in the Lapidarium of Marbodus:

"By the Red Sea the swarthy Arabs glean

The iris, splendent with the crystal's sheen;

Its form six-sided, full of heaven's own light,

Has justly gained the name of rainbow bright."

THE AVENTURINE.

The aventurine is a quartz of a clear brown or reddish-white colour, sprinkled with little spangles of yellow mica, that glitter like gold. It has been found also with a ground colour of yellow, of light gray, and of greenish-white.

The yellow variety has been called sunstone. It is very scarce, and exceedingly beautiful.

All aventurines do not owe their reflections and glitter to particles of mica. There is a kind--and that too pre-eminently esteemed--in which effects of this kind are produced by the presence of little crystals of quartz scattered through the mass, and reflecting the light on all sides. This last variety has generally a very clear tint of greenish-white, or sometimes of a reddish-brown.

The aventurine with mica was formerly brought from the borders of the White Sea; but at present it is furnished by Silesia, Bohemia, Siberia, and France. The species with crystals comes from Spain, and has for some years been produced by Scotland also.