Siliceous Genus. 125 



It never conftitutes veins or ftrata, but is 



either found in loofe mafies at moft 2 inches 



long, or mixed with fand or clay, or imbo- 



died in other ftones, as granites, &c. 



100 parts of the white contain about 67 

 of filiceous Earth, 14 of argillaceous, if of 

 ponderous, and 8 of magnifia. 



The fpecific gravity of the fpecimen I tried 

 was 2,542, 



Labrador Jlone is of this fpecies ; it reflects 

 the colours of the rainbow, is fomewhat 

 fofter than common felt-fpar, and is found 

 in pretty large pieces, generally of a dark 

 grey colour : its fpecific gravity is 2,755. 



Felt-fpar is undoubtedly the ftone which 

 the Saxons ufe as petunfe in their porcelain 

 manufactories. 3 Berlin Befchaftig. p. 471;. 



SPECIES XII. 



Siliceous Zeolyte. 



This differs from that defcribed under the 

 argillaceous genus only in this, that it gives 

 fire with fteel. It is white, and found at 

 3 Bergm. 224. It is very rare. 



SPECIES XIII. 



