This raw material lies between approximately negative 1 and 4 on the phi scale of particle size, and is often mixed with sodium carbonate and calcium carbonate to lower its melting point.
Localized overheating of this material leads to burn-on, which can proceed by vapor penetration. Coal dust is added to this material to provide a reducing environment and improve the collapsibility. It is mixed with a resin and forced into position by a pneumatic rammer before the resin is allowed to cure in the "air set" process, which allows for an improved surface finish. This material can be mixed with bentonite to improve its refractory properties, and that (*) "green" type of it is used to make holding flasks, whose two halves are called the cope and drag. This raw material lies between approximately negative 1 and 4 on the phi scale of particle size, and is often mixed with sodium carbonate and calcium carbonate to lower its melting point. For 10 points, name this most common material for casting molds, which is also the main precursor of glass.
Localized overheating of this material leads to burn-on, which can proceed by vapor penetration.
sand [prompt on quartz or silicon dioxide or SiO2 or silica, accept green sand before "sodium"]