Chap. 21.] orALS. 415 



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

 chrysoprasus. 45 In the fourth rank are reckoned the hyaein- 

 tlnue 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 arc 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 

 elongated* 1 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 thorn upon the; bristles of. 

 the elephant. It is generally agreed, however, that tJio*<: 

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

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

 Htud.s of gold. Tiiey 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, 58 and that 

 when pierced they become improved in colour; the 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 thu 

 diminution in their thickness. In addition to the defects 

 already 59 mentioned, and which are pretty nearly the same as 

 those to which the smaragdus is subject, beryls are affected with 

 cloudy spots, 60 like those on the finger-nails in appearance. In 

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

 found in the countries that lie in the vicinity of Pontus. 61 The 

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

 imitating various precious stones, beryls in particular. 



CHAP. 21. (G.) OPAI.S: SKVKX VARIETIES OF THEM. 

 Opals'' 2 are at once very similar to, and very different from, 



" 4i 1,1'rk-Krocn ami pold." M ".Sky-coloiirnl." 



17 The fargest specimen of Uml known, belonged -to Don P*lro. It 

 was not cylindrical in Corn), but shaped liku the head of a calf, ami weighed 

 22 o oimcoH troy. 



* Which in the case. " In Chapter 18 of this Book. w " Pterygia." 



Cl Jn the Uralian Mountains, for example. 



6 - Opals are hydrated bilicu, the amount of water varying. 



