to6 A SYSTEM OF 



2. Of hexagonal horizontal plates, Brufa 

 micacea conftans fquamis hexagonis hori- 

 zontalibus. This is found in the mines 

 at Salberg, in the province of Weft- 

 manland. 



SECT. XCVI. 



Observation ontheMic^;,orGLiMMERS, 



The flones belonging to this order are by mod 

 authors con fide red as Apyri, which they really 

 are in fome degrees of heat, and when they are 

 mixed with certain bodies : but they may at the 

 fame time with equal propriety be called Vitre- 

 fcents, both, per fe or by themfelves, becaufe they 

 melt with that deoree of fire in which neither 

 quartz nor limeitone are in the leaft altered ; and 

 are ftill more readily fufed, when mixed with a 

 martial earth, either by nature or art : hence, if 

 hornberg is naturally mixed with copper ores, as 

 is frequently found in Sweden, it is no way de- 

 trimental to the fmelling of them, as they com- 

 monly contain a fufficient quantity of fulphureous 

 acid, which fcorifies the iron. But when the glim- 

 mer is mixed with quartz, it may perhaps be impof- 

 fible to melt it, becaufe it renders the quartz fo 

 compact, as to prevent it from cracking, which may 

 be feen on the rock-ftone (Seel, eclxii.) : The mica 

 does the fame, when it is interfperfed in an apyrus 

 clay •, and this is the reafon why the ollaris fo 

 ftrongly refifts the fire. 



The mica has in fome degree the fame qualities as 

 an argillaceous earth ; but, for want of fufficient 

 experiments andobfervations, we cannot yet aflert 

 it to be a product of clay. 



The 



