Page:Theophrastus - History of Stones - Hill (1774).djvu/89

 keep his Countenance when he ees the Diamond reduced to a Species of Allum; and the Emerald of Borax, Foils Arrang'd, p. 137, 138.

What can be acertained in general is this:

The Mas of contituent Matter in them all, is a pellucid crytalline Subtance, which is in different Kinds of different Degrees of Hardnes, from that of the Diamond to that of the meret hattery Crytal. This crytalline Matter, had it concreted in perfect Purity, had been colourles alike in all: and the various Species had been ditinguihable only by their different Degrees of Hardnes: but as this Matter, in the time of its Coalecence, aumed into it any Particles of a proper degree of Gravity and Finenes, which happened to float in its Way, it became by that Means different not only in Colour, nay, and in Degree of Colour, according to the Nature and Quantity of the Particles it took up into itelf; but from their different Nature was alo altered in what alone could have been its determinate Characteritics, its Hardnes and pecific Gravity. Many Reaons may be alledged why the Particles thus aumed into the crytalline Nodules at the Time of their Formation, mut have been principally of the metalline Kind; and: we find, in effect, that they were o. The various Colours of the Gems have their Rie from thee Admixtures; and, according to what I have before oberved as to the colouring of Spars by the ame Means, when the metalline Matter thus mixed with the crytalline was Lead, the Stone became a Topaz, or, as the Antients called it, a Chryolite: for it is very evident, that what they called the Topaz, we now call the Chryolite; and what they called the Chryolite, we now, on the contrary, call the Topaz.

Our Topaz is a very elegant and very beautiful Gem, of which the Jewellers have two Kinds, the Oriental and Occidental; the Oriental are of a fine pale yellow like the Jonquil Flower. They are of very great Splendour, and equal the Ruby in Hardnes. Thee are brought from Arabia, and many Parts of the Eat Indies. The Occidental are often very beautiful; but are ditinguihed from the Oriental by their Softnes, for they are no harder than common Crytal: and by a foxy rednes with the yellow. We have them from Sileia and Bohemia.

The Topaz of the Antients, now called the Chryolite, differs from thee in Colour, for it has always an Admixture of green with the yellow; probably from Particles of Copper diolved in an Acid, and taken up with thoe of the Lead into the Matter of the Gem, at the Time of its original Concretion.

As thee Gems have their Colours from this accidental Admixture of extraneous Particles, they may alo be diveted of them by Fire; without any Injury to their Texture: and the Oriental Topaz thus rendered colourles, is, like ome other Gems to be hereafter decribed, ometimes made to counterfeit a Diamond.