Chap. 21.] OPALS. 415 



colour, and thought by some to constitute a separate genus, is 

 chrysoprasus.^' In the fourth rank are reckoned the hyacin- 

 thine beryls; and in the fifth, those known as *' aeroides."^ 

 Next, we have the wax-coloured beryls, and, after them, the 

 oleaginous beryls, so called from the resemblance of their colour 

 to that of oil. Last of all, there are the stones which closely 

 resemble crystal in appearance ; mostly disfigured by spots and 

 filaments, and of a poor, faint, colour as well ; all of them so 

 many imperfections in the stone. 



The people of India are marvellously fond of beryls of an 

 vlongated^^ form, and say that these are the only precious stones 

 they prefer wearing without the addition of gold : hence it is 

 that, after piercing them, they string them upon the bristles of 

 the elephant. It is generally agreed, however, that those 

 stones should not be perforated which are of the finest quality ; 

 and in this case they only enclose the extremities of them in 

 studs of gold. They prefer, too, cutting the beryls in a cylin- 

 drical form, instead of setting them as precious stones ; an elon- 

 gated shape being the one that is most highly esteemed. Some 

 are of opinion that beryls are naturally angular, ^^ and that 

 when pierced they become improved in colour ; Jhe white sub- 

 stance being thus removed that lies within, and their brilliancy 

 heightened by the reflection of the gold in which they are set ; 

 or, at all events, their transparency being increased by this 

 diminution in their thickness. In addition to the defects 

 already^^ mentioned, and which are pretty nearly the same as 

 those to which the smaragdus is subject, beryls are aff'ected with 

 cloudy spots,^° like those on the finger-nails in appearance. In 

 our own part of {he world, it is thought that they are sometimes 

 found in the countries that lie in the vicinity of Pontus.^^ The 

 people of India, by colouring crystal, have found a method of 

 imitating various precious stones, beryls in particular. 



- CHAP. 21. (6.) — opals: seven varieties of them. 

 Opals^^ are at once very similar to, and very difi'erent from, 



65 " Leek-green and gold." ^6 « Sky-coloured." 



" The largest specimen of Beryl known, belonged to Don Pedro. It 

 was not cylindrical in form, but shaped like the head of a calf, and weighed 

 225 ounces troy. 



58 Which is the case. 59 i„ Chapter 18 of this Book. ^^ " Pterygia." 



«^ In the Uralian Mountains, for example. 



62 Opais are bydrated silica, the amount of water varying. 



