MINERALOGY. 



SECT, ccxcv; 



A* Iceland agat, Achates ijlandicus nigerl 



It is black, (olid, and of a glaffy texture j 

 but in thin pieces, it is greenifh and femi- 

 tranfparent like glafs bottles, which con- 

 tain much iron. The molt remarkable is, 

 that fuch large folid malTes are found of it, 

 that there is no pcffibility of producing the 

 like in any glafshoufe. 



It is found in Iceland, and in the Ifland 

 of Aicenfion : The jewellers employ it as 

 an agat, though it is too foft to refill wear. 



SECT. CCXCVI. 



B. Rhenifh millftone, Lapis molaris Rhenanus2 

 Is blackifh grey, porous, and perfectly re- 

 fembles a lbrt of flag produced by Mount 

 Vefuvius. If I am miilaken in this', I hope 

 that fomebody elie will defcribe the con* 

 ftituent parts of this millftone. 



SECT. CCXCVII. 



C. Pnmice-ftone, Pvmex. 



h very porous and bliftered, in confe- 



quence of which it is ipecifically very li ,-ht. 



It refembles that froathy flag which is pro* 



duced in our iron furnaces. 



i. White. 



2. Black. 



The colour of the firfl is perhaps 

 faded or bleached, becaufe the fecond 

 kind comes in that ftate from the labora- 

 tory itfelf, viz. the volcanos. 



SECT, 



