Silicate minerals are rock-forming minerals made up of silicate groups. Equivalent reagents include sodium aluminate and sodium silicate. Hydrolysis is a chemical weathering process affecting silicate and carbonate minerals. Precipitated silica or amorphous silica is produced by the acidification of solutions of sodium silicate. Silica is also added, resulting in the production of calcium silicate slag. Talc is a clay mineral composed of hydrated magnesium silicate with the chemical formula MgSiO(OH). This is a soft clay-like material occurring naturally as an impure hydrous aluminium silicate. These generally occur in association with larger intrusions of alkali-rich silicate igneous rocks. It is composed of clay colored by iron oxide, magnesium, aluminum silicate, or potassium. The two major types are silicate based and carbonate based. Zircon is actually the mineral name for naturally occurring zirconium silicate (ZrSiO). Glass disease is the corrosion of silicate glasses in aqueous solutions. Clastic sedimentary rocks are composed of other rock fragments that were cemented by silicate minerals. The alite found in Portland cement differs in composition from simple tricalcium silicate. An example is porcelain, which is based on the silicate mineral kaolinite.