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The Precious Stone Usually Found In The Primitive Rocks, The Topaz

The name topaz is derived from the Greek topazos, which is the name of a small island situated in the Gulf of Arabia, from whence the Romans obtained a mineral which they called topazos and topazion, which mineral to-day is termed chrysolite.


The mineral topaz is found in Cornwall and in the British Isles generally; also in Siberia, India, South America and many other localities, some of the finest stones coming from Saxony, Bohemia, and Brazil, especially the last-named.

The cleavage is perfect and parallel to the basal plane.
It crystallises in the 4th (rhombic) system; in lustre it is vitreous; it is transparent, or ranging from that to translucent; the streak is white or colourless.
Its colour varies very much—some stones are straw-colour, some are grey, white, blue, green, and orange.

A very favourite colour is the pink, but in most cases this colour is not natural to the stone, but is the result of "burning," or "pinking" as the process is called technically, which process is to raise the temperature of a yellow stone till the yellow tint turns to a pink of the colour desired.


The topaz is harder than quartz, as will be seen on reference to the "Hardness" table, and is composed of a silicate of aluminium, fluorine taking the place of some of the oxygen.

Its composition averages 16.25 per cent. of silica, 55.75 per cent. of alumina, or oxide of aluminium, and fluoride of silicium, 28 per cent. Its formula is [Al(F,OH)]2 SiO4, or (AlF)2SiO4. From this it will be understood that the fluorine will be evolved when the stone is fused.

It is, however, very difficult to fuse, and alone it is infusible under the blowpipe, but with microcosmic salt it fuses and evolves fluorine, and the glass of the tube in the open end of which the stone is fixed is bitten with the gas.

Such experiments with the topaz are highly interesting, and if we take a little of the powdered stone and mix with it a small portion of the microcosmic salt, we may apply the usual test for analysing and proving aluminium, thus: a strongly brilliant mass is seen when hot, and if we moisten the powder with nitrate of cobalt and heat again, this time in the inner flame, the mass becomes blue.

Other phenomena are seen during the influence of heat.
Some stones, as stated, become pink on heating, but if the heating is continued too long, or too strongly, the stone is decoloured.
Others, again, suffer no change, and this has led to a slight difference of opinion amongst chemists as to whether the colour is due to inorganic or organic matter.

Heating also produces electricity, and the stone, and even splinters of it, will give out a curious phosphorescent light, which is sometimes yellow, sometimes blue, or green.
Friction or pressure produces strong electrification; thus the stones may be electrified by shaking a few together in a bag, or by the tumbling of the powdered stone-grains over each other as they roll down a short inclined plane.

The stones are usually found in the primitive rocks, varying somewhat in different localities in their colour; many of the Brazilian stones, when cut as diamonds, are not unlike them.

In testing, besides those qualities already enumerated, the crystalline structure is specially perfect and unmistakable.
It is doubly refractive, whereas spinel and the diamond, which two it closely resembles, are singly refractive.

Topaz is readily electrified, and, if perfect at terminals, becomes polarised; also the commercial solution of violets, of which a drop only need be taken for test, is turned green by adding to it a few grains of topaz dust, or of a little splinter crushed to fine powder.


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