Cordierite is a mineral that occurs naturally but also a manufactured ceramic. The first contact that most potters and technicians have with it is cordierite kiln shelves, but cordierite parts can be found in heaters and appliances at your home and work. These are made from magnesia, alumina and silica sourcing materials (e.g. talc or magnesite, kaolin, silica, alumina). You can calculate the mix of materials needed to achieve the formula 2MgO.2Al2O3.5SiO2. The mix is formed and fired in oxidation to high temperatures (around cone 14) to form the desired crystalline phase.
Cordierite has an extremely low thermal expansion and low thermal conductivity (1 x 10-6), it is thus very resistant to thermal shock (so resistant that it can survive quenching in water from red heat). It is moderately refractory, sufficient to handle duty as kiln shelves at cone 10, but no higher than about 1350C.
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Refractory, as a noun, refers to a material that does not melt at normal kiln temperatures (of the industry being referenced). The term also refers to the capacity a material to withstand heat without deforming or melting. Kiln shelves and firebricks are refractory. Many natural clays and minerals a...