Sep 30, 2016· Feldspar containing a certain proportion of quartz is saleable; No. 1 contains less than 5% of quartz, No. 2 up to 15% or 20%, and No. 3, still higher, but not over 30%. Microcline and orthoclase are the varieties of feldspar commonly mined. Users prefer a potash feldspar, but the soda feldspar, albite, is used to some extent.