Phillipsite is a mineral of the zeolite group; a hydrated potassium, calcium and aluminium silicate, approximating to (Ca,Na₂,K₂)₃Al₆Si₁₀O₃₂·12H₂O. (Also with sodium replaced by calcium: KCaAl₃Si₅O₁₆·6H₂O ). The crystals are monoclinic, but only complex cruciform twins are known, these being exactly like twins of harmotome. Crystals of phillipsite are, however, usually smaller and more transparent and glassy than those of harmotome. Spherical groups with a radially fibrous structure and bristled with crystals on the surface are not uncommon. The Mohs hardness is 4.5, and the specific gravity is 2.2. The species was established by A. Lévy in 1825 and named after William Phillips. French authors use the name Christianite (after Christian VIII of Denmark), given by A. Des Cloizeaux in 1847.