The Topaz- Occidental and Oriental

The topaz, like its kindred precious stones, is divided into the occidental and the oriental.

The oriental topaz should be in every respect carefully distinguished, because it is the only variety which is composed of alumina nearly pure. The others contain no more than 57 or 58 parts to 100 of this substance.

The topaz of the moderns is the chrysolite of the ancients. It is a corundum coloured by a slight quantity of the oxide of iron to a beautiful golden yellow. The topaz was originally found, as Pliny informs us, upon an island in the Red Sea, which, being often surrounded by fog, was so difficult to find that the mariners named it Topaza (Gr. topazein, to guess).

This stone is now very rare; and when to the fineness of its quality it joins a soft clear colour with a satin-like lustre, it acquires a considerable value. But the topaz, however perfect, never reaches the price of a ruby or a sapphire, or even a fine emerald of equal dimensions.

Occidental Topaz.--Stones thus designated are not corundums. They are of a more complex composition; and the analysis of specimens brought from different localities proves that occidental topazes are not identical. They have for a long time been divided into four varieties:--

Brazilian Topaz. Mexican Topaz.

Saxon Topaz. Siberian Topaz.

It should be remarked, however, that while the proportions of the elements differ in each of these varieties, their nature is the same. The occidental topaz is in all cases formed of alumina, silica, and fluoric acid. The presence of this last substance, found in no other precious stone, characterizes perfectly the genus topaz in respect to chemical composition.

The primitive type of crystals of topaz is the right rhomboidal prism (Fig. 58).

Certain modifications occur in the form of these crystals, which, joined to their colour, enable a person to decide as to which of the varieties any topaz in question belongs.

The Saxon topaz generally occurs in the form of a rhomboidal prism with a base; and its colour varies from an orange yellow to a straw yellow.

The Brazilian topaz exhibits most frequently a rhomboidal prism surmounted by a four-faced pyramid, and its colour includes all the shades from orange yellow to wine yellow.

The Siberian topaz is nearly always found in rhomboidal prisms, terminated by a ditetragonal pyramid; it is of a pale blue or green cast of colour, and sometimes occurs colourless, when it is much prized. Although in form of crystallization these Siberian minerals are really topazes, they approach very nearly by their tint and transparency to the aquamarine.