What mineral is in porcelain sinks?

Aluminous porcelain. Porcelain is a glass product with a crystalline internal structure. In the case of porcelain used in sinks and toilets, the crystalline inclusions are mostly aluminum oxide which makes the glass tough and difficult to break. It also makes the porcelain opaque. Aluminum oxide is also used in the formulation of the glass matrix as a stabilizer. In this form, the aluminum oxide does not affect the translucency of the glass, but, rather makes it stronger and reduces the solubility of the glass.