PHILLIPSITE  , a

mineral of the zeolite group; a hydrated potassium, calcium and aluminium silicate, approximating to (K2, Ca)AI2(SiOa)4.4H2O . It varies somewhat in composition, and a variety (" pseudophillipsite ") containing rather less silica has the formula (K.2, Ca)2Al4Si5018.9H20 . Crystals are monoclinic, but only complex cruciform twins are known, these being exactly like twins of harmotome (q.v.) . 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 42, 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 .