Feldspars -LRB- KAlSi3O8 - NaAlSi3O8 - CaAl2Si2O8 -RRB- are a group of rock-forming tectosilicate minerals which make up as much as NUMBER@1 % of the LOCATION@1 's crust .

Feldspar is the name of a group of rock-forming minerals that make up as much as NUMBER@1 % of the LOCATION@1 's crust .
