84:4 NEW YOKK STATE MUSEUM 



quartz i3 sold for about $3 a ton. The percentage of ferric oxid 

 in the material influences its commercial value to a large degree, 

 as, in the manufacture of white earthenware or porcelain, it is 

 highly essential that the iron percentage in the mixture shall be 

 extremely low. For this reason many deposits of feldspar, which 

 would otherwise be of commercial value, are left untouched. 



