ANALCIME, a common mineral of the zeolite group. It crystallizes in the cubic system, the common form being the icositetrahedron (2 I I ), either alone or in combination with the cube (Foo) . The crystals are often perfectly colourless and trans parent with a brilliant glassy lustre, but some are opaque and white or pinkish-white. The hardness is 5 to 51, and the specific gravity 2.25. Chemically, analcime is a hydrated sodium and aluminium silicate, Before the blowpipe the mineral readily fuses with intumescence to a colourless glass. It is decomposed by acids with separation of gelatinous silica. Analcime usually occurs, associated with other zeolitic minerals, lining amygdaloidal cavities in basic volcanic rocks such as basalt and melaphyre. The Tertiary basalts of the north of Ireland frequently contain cavities lined with small brilliant crystals of analcime. Larger crystals of the same kind are found in the basalt of the Cyclopean islands, Sicily. Large opaque crystals of the pinkish-white colour are found in cavities in melaphyre at the Seisser Alpe in southern Tirol.