Original: Feldspars ( KAlSi3O8 - NaAlSi3O8 - CaAl2Si2O8 ) are a group of rock-forming tectosilicate minerals which make up as much as 60 % of the Earth 's crust .
Simplified: Feldspar is the name of a group of rock-forming minerals that make up as much as 60 % of the Earth 's crust .