Laumontite and Chabazite Composition, Crystallization & Structure
Laumontite
A zeolite with composition H4CaAl2Si4O14.2H2O. Monoclinic In prismatic crystals with oblique terminations; columnar. Cleavage parallel to prism and clinopinacoid. H. = 3.5-4. G. = 2.25-2.35. vitreous to pearly luster. Colour white or Gray. Alters on exposure, becoming opaque and pulverulent. Fusible (25). Gelatinizes in acids. Water in C. T. found as a mineral of secondary origin in cavities of basic igneous rocks, associated with other zeolites, etc.
Chabazite
Composition. Usually corresponds to (Ca,Na2)Al2Si4O12.6H2O but different analyses show considerable variation from this formula, so that the composition is still uncertain.
Crystallization. Hexagonal rhombohedral. Common form is the simple rhombohedral r, having nearly cubic angles. May show several different rhombohedrons (Fig. 342). Often in penetration twins.
Structure. Usually in crystals.
Physical Properties. H. = 4-5. G. = 2.05-2.15. vitreous luster. Colour white, yellow, fleshed. Transparent to translucent.
Test. Fuses with swelling at 3. decomposed by hydrochloric acid whit the separation of silica but without the formation.
Of a jelly. Solution after filtering off silica gives precipate of aluminium hydroxide with ammonia, and in filtrate ammonium carbonate gives white precipate of calcium carbonate. Gives much water in C. T. recognized usually by its crystals.
Occurrence. A mineral of secondary origin found usually with other zeolites, lining amygdaloidal cavities in basal. Notable way, Ireland; at Assign, bohemia; Seicer Alpo, trending, Italy; Obersetein, Germany; West Paterson, etc., jersey; gobble station, Oregon; in Nova Scotia, etc.
Name. Chabazite is derived from a Gleek Word which was an ancitied name for a stone.
Gmelinit, (Na2,Ca)Al2Si4O126H2O, is closey related to chabazite but rarer in occurrence.
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