18 DOMAIN VII. COMPOSITE. 



colour of the chalcedony is a bluish grey; but it 

 also appears of a yellowish white, and often co- 

 vered with ferruginous rust. Sometimes there 

 are zones, concentric and in festoons, of a paler 

 colour. The fracture is various, sometimes uni- 

 form, sometimes scaly, sometimes a little con- 

 choidal; and its hardness is such that the file 

 cannot touch it. It is coeval with the granite, 

 for nodules of granite may be found in the chal- 

 cedony, as well as the contrary. These granitic 

 nodules contain very little mica, but abundant 

 felspar, yellow or reddish, and quartz, of which 

 the aspect sometimes approaches that of the 

 chalcedony. The pyrites is interlaced in a re- 

 markable manner, being in plates nearly regu- 

 lar, a quarter of a line in thickness, and about 

 five or six lines in length. These plates cross 

 each other in certain places, in every direction. 

 Each of the plates is included in a kind of sal- 

 band, of a breadth equal to that of the plate, of 

 a deeper coloured chalcedony than the rest of 

 the stone. The pyrites is of a pale brass co- 

 lour, and granular fracture, but decomposes in 

 the air; so that its beauty only becomes ap- 

 parent on a fresh fracture*. 



* Saussare afterwards discovered abundance of chalcedony in 

 the granites and gneiss of the plains, and particularly in the ancient 

 Bourbonnois. See tome v. p. xi. 



