Feldspar comprises by far the largest group of minerals found in the earth’s crust. Feldspar minerals are the primary components of volcanic, metamorphous and sedimentary rock, which means some 60% of the earth’s rock is made of feldspar. Most European deposits contain potassium feldspar as well as sodium feldspar and feldspar composites. Various types of feldspar are widely used in industrial applications thanks to their aluminium oxide content. Chemically speaking, feldspar minerals are aluminium silicates with traces of sodium, potassium, iron, calcium, barium or combinations of these elements. In particular, the potash feldspar minerals supplied by the Quarzwerke Group are low in iron content and widely used in a variety of applications.