The protons in crystal structures can be related to the oxygen lattice through several spatial arrangements. In orthosilicates (for example, hydrogarnets), so-called tetrahedral hydroxyls have been demonstrated by indirect methods. Similar methods, when applied to kehoeite and viséite, lead to the conclusion that (H 3 O 2 ) - units can occur in the framework of analcime, a structure in which all apexes of oxygen tetrahedra are shared.