u/4 Elements of Mineralogy. 



Pfeudopal is opake, and reflects green and 

 yellow rays, and hence called cat's eye. 



Avantunne refembles an opal with gold 

 fpecks, but is a product of art. 



III. VARIETY. 

 Chakedonian. 



Its colour is a bluifh cloudy white, or grey, 

 with {hades of other colours, and tranfverfely 

 infpecled prefents an iris ; when white and 

 opake it is called chachelong : its fpecific gra- 

 vity, according to Mr. Bergman, is from 2,5 

 to 4,36. Stones of this latter weight muft 

 be very different from thofe of the former. 

 Thefe ftones fometimes contain water. It is 

 affe&ed by the ufual fluxes, as flint. 



, According to the experiments of Mr. 

 Bergman^ the chalcedony of Fero contains 

 84 per cent, of lilex and 1 6 of argill. Mr. 

 Bindheini found another fort to contain 83,3 

 of filex, ii of calcareous Earth, and 1,6 of 

 argill, befides a minute portion of iron. 3 

 .Schrift. Nuturfor. Freunde y p. 429. 



Opals and chalcedonies, which by admit- 

 ting water within their pores become tranf- 

 parent, are called hydrof banes. This phoe- 



nomenon 



