44 Photos
Phillipsite
Chemical Formula	(Ca,Na2,K2)3Al6Si10O32·12H2O
Species	Silicates
Crystal System	Monoclinic
Mohs Scale	4
Specific Gravity	2.2
Color	White
Streak	White
Luster	Vitreous
Refractive Index	n = 1.483 - 1.505 n = 1.484 - 1.511 n = 1.486 - 1.514

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.

Phillipsite is a mineral of secondary origin, and occurs with other zeolites in the amygdaloidal cavities of mafic volcanic rocks: for example in the basalt of the Giants Causeway in County Antrim, and near Melbourne in Victoria; and in Lencitite near Rome. Small crystals of recent formation have been observed in the masonry of the hot baths at Plombires and Bourbonne-les-Bains, in France. Minute spherical aggregates embedded in red clay were dredged by the Challenger from the bottom of the Central Pacific, where they had been formed by the decomposition of lava.