106 Elements of Mineralogy. 



The Coloured Opake Quartz are either. 



Blacky being mixed with a large proportion 

 of iron. 



Red, according to Cronfted they contain 

 copper, but Mr. Bergman could find none in 

 them. 2 Bergm. 430. 



Blue, from Uto in Sweden. 



Green> found at Adelfdorfm Sweden^ 



SERIES III. 

 Arenaceous Quartz or Sand. 



Though the powdery ftate of other ftones 

 does not defer ve any particular notice: yet that 

 of quartz or filex does, from the great ufe that 

 is made of it, and from its feeming to poflefs 

 properties which are incompatible with it in a 

 grofler ftate. It is of various colours and 

 incapable of forming a mafs or hardening 

 with water, the pureft is white, the minute 

 particles of which, when infpe&ed through a 

 lens are tranfparent. It is feldom perfectly 

 pure ; Mr. Achard fays that the fine white 

 fand of Freyenivald, which is ufed for the 

 porcelain manufactories contains % of its 

 weight of argill and calcareous Earth, but 

 this I fhould rather take to be a petro-filex 



in 



