Feldspars - all about the plagioclases and K-feldspars
Feldspars are alumosilicates of alcalic metals and form a significant portion of many volcanic and metamorphic rocks. As such, they are one of the most important mineral groups on the Earths surface: some estimate that they form between 50-60 % of the Earths crust. Their content in most sedimentary rocks is much less significant.