hydrated calcium, sodium, and potassium aluminosilicate mineral in the zeolite family 【(K,Na,Ca)_1-2(Si,Al)₈O₁₆·6H₂O】. It typically is found as brittle white crystals filling cavities and fissures in basalt and in phonolite lava, occurring near Rome; on Sicily; in Victoria, Australia; and in Germany. Phillipsite's molecular structure is a framework containing rings of four or eight linked silicate or aluminate tetrahedra (each consisting of four oxygen atoms arranged at the points of a triangular pyramid about a central silicon or aluminum atom); the openness of this structure and the presence of the aluminum atoms (each of which contributes a negatively charged site) give phillipsite cation-exchange properties (dissolved sodium, potassium, calcium, and magnesium readily replacing one another in the structure), making phillipsite useful in water softeners (water softener). For detailed physical properties, see zeolite (table). Compare harmotome.