356 THE DIAMOND AND OTHER PRECIOUS STONES. 



ing to its width, gives a peculiar tint similar to the eifect produced by 

 j)ressing two i)lates of glass together : we may recognize violet, blue, 

 indigo, red, yellow, and green, the last two being exhibited more rarely 

 than the others. 



As a proof that the brilliant colors of the opal are due, as we have 

 said, to narrow fissures, similar colors may be produced by partially 

 fracturing, with the blow of a hammer or a wooden mallet, a cube of glass 

 or even a rock-crystal. Colors obtained in this way are known in optics 

 by the name of colors of thin plates, and are of the same character as 

 those of flowers, which result from the overlaying of the transparent 

 tissues of which the petals are composed. Herein lies the secret of all 

 their varied hues from their first opening until their final decay. 



Sometimes the opal is colored only in its substance, has not so great 

 a play of light as when it is variously traversed by fissures, and then it 

 is not so much esteemed. Again, it may have extended fissures exhibit- 

 ing a somewhat changeable single color — red, blue, yellow, or green. 

 The Empress Josephine once paid a very high price for a pair of these 

 stones, it being then the fashion to wear two bracelets exactly alike, 

 and it was quite diificult to get two stones perfectly- matched, since the 

 interior disposition of the fissures of the opal, which gives its peculiar 

 plaj of color, depends entirely upon accident. At present it is only the 

 harlequin opals that are much valued, and those of Josephine would 

 not now bring a tenth of their former cost. 



Except for ear-rings, the opal should be set singly, with or without a 

 surrounding of small brilliants, whose vivid lusters and scintillations 

 contrast favorably with the tints of the opal. 



The opal is not a very hard stone. In its chemical composition it is 

 only hydrated quartz — that is, white pebble, combined with water. 

 Heat, expanding its fissures, varies its colors, and pressure obviously 

 produces the same effect. I have thus often changed, without perma- 

 nent alteration, the colors of a beautiful Hungarian harlequin opal. 



Before the revolutionary tempest, in the closing years of the past cen- 

 tury, the financier d'Auguy possessed a harlequin opal of great beauty. 

 It was a perfect oval, 121 millimeters long, and from 15 to IG millimeters 

 in breadth. Esteemed as entirelj^ perfect, the stone had a great celeb- 

 rity. I do not know if d'Augny ran, like the senator iSTonius, any risk 

 of proscription during the years of terror; but certainly if he did, it was 

 not on account of his possession of this unparalleled opal, since the 

 wretched tyrants of '93, who sold to foreigners the treasures of St. 

 Denis, and of many other churches, for 80,000 francs, did not dream of 

 opals exhibiting all the colors of the rainbow. 



The opal of d'Augny, the value of which I have nowhere seen esti- 

 mated, passed some time ago into the hands of Count Waliski. The opal 

 of Nonius, of the size of a hazel-nut, which he selected from among all 

 his treasures as the companion of his exile, was estimated at 20,000,000 

 sesterces, which, according to the exact table of M. Dureau de la Malle, 



