Silica – SiO2 (m.p. 3119oF/1715oC) is second only to clay in significance as a ceramic material, and it is the most abundant mineral in the earth»s crust. Silica is frequently referred to as “Flint and is often just ground sandstone. It is used interchangeably with Quartz. Silica or Quartz is used in clay bodies to modify shrinkage, porosity, and strength. Quartz has a phase transition at 1063o F/573o C, i.e. the Quartz Inversion. Upon firing, this inversion occurs rapidly and results in volume expansion, which can lead to firing cracks in clay bodies high in Free Quartz. In glazes, Silica is the most common glass former and decreases thermal expansion.It is also used to increase the melting temperature.