Quartz and feldspar are two of the most common minerals found in the Earth's crust. They are both silicate minerals, meaning they contain silicon and oxygen atoms. Quartz is a hard, crystalline MINERAL that is usually white or colorless, while feldspar is a softer, more granular MINERAL that can be found in a variety of colors. Both quartz and feldspar are used in a variety of industries, from construction to electronics.