( 71 ) 



mieu has obferved, and as I have fince found 

 by experiment, are little inferior, in that 

 quality, to rock cryftal. 



The three other fpecies do not effentially 

 differ from feveral defcribed by Wallerius, 

 Born, Bergmann, Faujas, and others, and 

 which are found in the ifland of Ferro, the 

 Vivarais, and other volcanized countries. 

 But the fixth fpecies appears to me new ; at 

 Jeaft, I have found no writer who mentions a 

 zeolite, conftantly cryftallized with eighteen 

 facets, as often as its cryftals are detached ; 

 nor do 1 know that any zeolite has hitherto 

 been difcovered which is equally clear and 

 brilliant. 



It appears that the true figure of the zeo- 

 lite is a cube ; at leaft, that it always affeds 

 that form where its cryftallizations meet 

 with no obftacles. According to circum- 

 flances it is more or lefs modified ; and the 

 tctrahedral prifms of the fourth or fifth 

 fpecies are probably one of thefe modifica- 

 tions. The firfl and fecond ^re amorphous ; 

 f 4 but 



