84 Elements of Mineralogy. 



cultly foluble compound^ and as many clays 

 are found to contain the marine acid, it is 

 probable that this fpecies exifts in them, 

 though it hath not yet been noticed. 



In ajlony Form. 



'Under this head I comprehend all thofe 

 ftones which, although the filiceous genus pre- 

 dominates in their competition, and the argil- 

 laceous, with refpect to quantity, obtains only 

 the fecond place, yet do not poffefs the cha- 

 racter of filiceous ftones, as they do not ftrike 

 fire with fteel ; and on the contrary, I exclude 

 thofe which poflefs the characters of filiceous 

 Earths, though they contain the argillaceous 

 in greater quantity 



SPECIES V. 



Arglll combined 'with 1,36 its weight of Silex> 

 >7 2/ *t s ^ tight of pure Mngnefia^ and 0,5 

 of its 'weight of highly dephlogijlicated Iron. 



Pure Mica. 



This ftone, in its pureft ftate, is colourlefs ; 

 but either from a leis intimate combination, 

 or from a mixture of fome fuperfluous ingre- 

 dient, principally iron, it is found of diffe- 

 rent colours, white, red, yellow, green, 

 brown, or black, ^the white and yellow fort 



havs 



