PHILLIPSITE, a mineral of the zeolite group; a hydrated potassium, calcium and aluminium silicate, approximating to (K 2 , Ca) Al 2 (SiO3).r4H 2 O. It varies somewhat in composition, and a variety (" pseudophillipsite ") containing rather less silica has the formula (K 2 , Ca) 2 Al 4 Si 5 Oi 8 -9H 2 O. 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 hardness is 4%, and the specific gravity 2-2. The species was established by A. Levy 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 basic volcanic rocks: e.g. in the basalt of the Giant's 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 Plombieres and Bourbonneles-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. (L. J.S.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)