Those minerals may contain hydrated or anhydrous arsenates. The system uses the reaction energy created when salts are hydrated or dehydrated. Talc is a clay mineral composed of hydrated magnesium silicate with the chemical formula MgSiO(OH). Increasing water concentration results in the formation of hydrated silica gels and colloidal silica dispersions. The 40-km thick solid outer crust is a mixture of ice, salts, and hydrated minerals. All phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached. It combines with water forming hydrated salts of various compositions. Hydrogen is present as water (HO) ice and in hydrated minerals. It hydrolyzes to a gel of hydrated titanium dioxide. Opals are composed of complicated crystalline aggregates of partially hydrated silicon dioxide. All the tetrahalides are readily hydrolyzed to hydrated germanium dioxide. Aluminium chromate conversion coatings are amorphous in structure with a gel-like composition hydrated with water. These halides exist in anhydrous and hydrated forms. An alternative indicator is methyl violet which is orange when dry and green when hydrated. This is ground to make hydrated lime powder.