19(5 A SYStEM OE 
2, Of hexagonal horizontal plates, BrUfd 
micacea confians fguamk hexagonis hork 
.zontalihus. This is found in the mines 
at Salberg, in the province of Weft*^ 
manland. 
SECT. XCVL 
Obs ER VAT ION on the Mic^, OrGLIMMERS^ 
The ftones belonging to this order are by mod 
authors confidered 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 deg-ree of fire in which neither 
quartz nor limeftone are in the lead: altered ; and 
are. ftill more readily fufed, when mixed with a 
martial earth, either by nature or art : hence, if 
hornherg 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 v/ith quartz, it may perhaps be impof- 
fible to melt it, becaufe it renders the quartz fo 
compa(d, as to prevent it from cracking, which may 
be feen on the rock-done (Se6l. cclxii.) ; The mica 
does the fame, when it is interfperfed in an apyrus 
clay ; and this is the reafon why the ollaris fo 
ftrongly refids the fire. 
The mica has in fome degree the fame qualities as 
an argillaceous earth ^ but, for want of fufficient 
experirnents andobfervations, we cannot yet afiert 
it to be aproduft of clay. 
The 
