Summary: Specimens of chlorophaeite and palagonite obtained from eight countries were examined using a variety of techniques. Investigations showed the materials to be not simple substances but multiphase composites. The confusion that existed in the literature necessitated a revision of the nomenclature and construction of criteria for identifying the two materials. Their nomenclature has been expanded: chlorophaeite to include the following phases; phase I, green and isotropic; phase II, golden yellow and isotropic; phase III, darker than phase II and anisotropic; a fourth phase, named associated material (A), microcrystalline, pale green and sometimes pleochroic. Similarly for palagonite, a golden yellow glassy phase, essentially basaltic glass (no new name needed); phase X, a hydrated phase slightly darker in colour than the glassy phase, also isotropic; phase Y, dark brown to orange, microcrystalline, anisotropic, found adjacent to phase X; associated material (M) green, anisotropic, often chlorite or chloritic. Both of the above descriptions were based on neotypes, established during the work. X-ray diffraction data for the two materials are given together with microprobe analyses of some of the phases of the two materials.