Hidrous Silicates - Zeolite Division, Subdivision, Apophyllite Composition

Composition. H7 Kca4 (SIO3)8. 41/2 H2O. Usually contains small amount of fluorine.

Crystallization. Tetragonal. Usually shows a combination of prism of second order, pyramid of firs and basal plane. Small faces of a ditetragonal prism sometimes observed. Prism faces show vertical striations and have a vitreous luster, while base shows pearly luster. Crystals may resemble an isometric combination of cube and octahedron, but are shown to be tetragonal by difference in luster between faces of prism and base.

Structure. In crystals; also massive and lamellar.

Physical Properties. Perfect basal cleavage. H. = 4.5-5. G. = 2.3-3.4. Luster of base pearly, other faces vitreous. Color usually colorless, white or grayinsh; may show pale shades of green, yellow, rose. Usually transparent, rarely nearly opaque.

Tests. Fuses easily with swelling to a white vesicular enamel. Colors the flame pale violet (potassium). Yields 16 per cent of water in C. T. Decomposed by hydrochloric acid with separation of silica but without the formation of a jelly. Solution gives little or no precipitate with ammonia, but gives an abundant white precipitate with ammonium carbonate (calcium carbonate). Recognized usually by its crystals, color luster and basal cleavage.

Occurrence. Occurs commonly as a secondary mineral lining cavities in basalt and related rocks. Associated with various zeolites, with calcite, datolite, pectolite, etc. Found in fine crystals at Bergen Hill, Paterson, ete., New Jersey; Lake Superior copper district; Nova Scotia; Guanjuato, Mexico; near Bombay, India; Andreasberg, Harz Mountains; Aussig, Bohemia; on the Seizer Alpe in Trentino, Italy; Faroe Islands; Iceland¡ Greenland, ete.

Name. Apophllite, named from two Greek words meaning get leaves, because of its tendency to exfoliate when ignited.