THE DIAMOND AND OTHER PRECIOUS STONES. 359 



the yellow variety, wliicli, strictly speakiug, onlj' ouglit to bear the name 

 oitojxxz, lias wonderfully declined during the last quarter of a century. 

 The Brazilian topaz cannot be confounded with the oriental, which is a 

 beautiful coriudon of a j'ellow color, deepening almost to orange. 



Although the topaz is not considered a very brittle mineral, it is said 

 that the Emperor Maximinius, who broke the teeth of his horse with a 

 blow of his fist, and the leg of a beast by one of his royal kicks, was so 

 strong in the hands that he could crush topazes as we crush a lump of 

 sugar. The topaz hris been for a long time a great favorite, esi)ecially 

 with the Spaniards, but with the caprice of fashion it has of late years 

 greatly declined in the estimation of the x)ublic. 



It was on the white topaz of Brazil that Fresnel made the important 

 discoveries of double refractiou with two axes. It is, also, the topaz 

 which bears the name of water-drop, which is made so often to pass for 

 the diamond. In mineralogy this stone serves as one of the types of 

 comparative hardness. Thus, we say a stone scratches glass, scratches 

 rock-crystal, scratches topaz and sapphire, according to the various 

 degrees of hardness. For example, the Brazilian topaz cannot scratch 

 sapphire, which is one test of a diamond. The black diamond of Borneo 

 scratches every stone, even diamond itself. As to the peridot and oj;o/, 

 they scratcli nothijig, not even ordinary bottle-glass, which I use in ex- 

 l>eriments of this kind ; as to window-glass it has become too soft of late 

 to be used as a test, since for economy it is now made with too large a 

 proportion of alkali. 



The blue topaz of Brazil has never as deep a tint as that of the 

 sapphire; it is only an aqua-marine of superior quality. Of all topazes, 

 the only one highly esteemed is that artificially colored, of a pale rose 

 hue, by means of fire. For the specimens that we wish to experiment 

 with we must choose those of a deep yellow or rich orange color. After- 

 ward they are placed in ashes or sand and submitted to a red, or even 

 a white heat, more or less i>rolonged. When they are taken out we 

 find the tint changed to the light red of w^hat is called ruhy halais or 

 ruby brulee, (burnt ruby.) The gay color of this ruby is very pleasing 

 to the eye. A dilettante once remarked to me, "This stone has an 

 amiable character." I w^as entirely of his opinion as to the moral of 

 this gem, although there is certainly nothing very sincere in the means by 

 which it acquires its beautiful tint. If, like the olivine, the topaz had 

 been enveloped in volcanic fires, it would naturally have become a ruhy 

 halais, and no cloud would have rested on the truthfulness of its 

 character. 



The mineral species which the topaz forms is characterized bj- a cer- 

 tain quantity of fluoric acid, which it contains exclusively of all other 

 gems. This stone, moderately heated, becomes electric and will attract 

 light movable bodies. A delicate linen thread, suspended vertically from 

 one end, is attracted by the warmed topaz as it would be by a stick of 

 sealing-wax after being rubbed on cloth. The topaz shares this curious 



