Arglllactoue Genus. 87 



brittle, and of a lamellar texture : its fpecific 

 gravity is 2,876: when in pieces of J of an 

 inch thick, or lefs, it gives a clear found if 

 ftruck : its grain is moderately fine : it is 

 never tranfparent: it flightly effervefces with 

 acids when reduced to powder, otherwife not : 

 when heated red, it lofes fomSthing more 

 than 2 per cent, of its weight, flightly 

 detonnates with nitre, and then affumes a 

 brownifh red colour, but calcination does not 

 render it magnetic : in a ftronger heat it is 

 fufible perje^ and forms a black fcoria : it is 

 difficultly diffolved by mineral alkali in the dry 

 way, more eatily by borax, though with lit- 

 l effervefcence, and alfo by microcofmic fait 

 with fome effervefcence, Mr Gerhard re- 

 marks, that it melts with equal eafe in chalk 

 or clay veflels. 



Dephlogifticated fpirit of nitre, after Hand- 

 ing on it two months in cold, affumes a greea 

 colour. 



I found 100 gr. of it to contain about 46 

 of filex, 26 of argill, 8 of magnefia, 4 of 

 calcareous Earth, and 14 of iron. Part of 

 the iron feems to be in a phlogifticated ftate, 

 from its union with the oil, and part in a 

 dephlogifticated ftate, or that of a red calx* 

 This is united to the argillaceous part and 

 filex, and is very difficultly feparated. 



64 



