Quartz is the mineral form of silica powder used in ceramic glazes and clay bodies. It is the mineral that silica “wants to be” when cooled from molten to solid (it can be other things depending on the speed of cooling) Quartz sand is often used in bodies as grog for texture and to increase thermal expansion. Powdered quartz is used in glazes and bodies also. Quartz of very fine particle size (-400 mesh) will typically enter the feldspathic melt or convert to cristobalite during firing if fluxes are lacking, coarse powdered grades help to ‘squeeze’ glazes into fit. Intermediate sizes (200-300 mesh) seem to be best however, since their greater surface area exerts more compressive squeeze per unit.