Also known as Flint or Quartz. This is the most common source of silica in clay bodies and glazes. Increases the thermal expansion in clays and decreases thermal expansion in glazes. Also used to raise the melting point in glaze. Silica is the most abundant mineral on the planet making up to 60% of the Earths crust. It is a hard glassy material with a melting point of over 3100°F. When blended with aluminum oxide and water, basic idealized clay is formed. When raw silica is added to clay bodies it introduces extra or ‘free’ silica that is not bound to the clay particles giving the body its strength.