Stilbite - Desmine Composition, Crystallization & Structure

Composition. (Na₂,Ca)Al₂Si₆G0₁₆G.6H₂O.

Crystallization. Monoclinic. Uniformly in cruciform twins. Commonly tabular parallel to elinopinaeoid. Crystals usually in sheaflike aggregates.

Structure. In crystals groups, divergent or radiated.

Physical Properties. Perfect cleavage parallel to clinopinacoid. H. = 3.5--4. G. = 2.1-2.2. Vitreous luster; pearly on clinopinacoid. Color white, yellow, brown, red. Translucent.

Tests. Fuses with intumescence at 3. Decomposed by hydrochloric acid with separation of silica but without the formation of a. Water in C. T. characterized chiefly by its cleavage, pearly luster on the cleavage face and common sheaflike groups of crystals.

Occurrence. A mineral of secondary origin found in amygdaloidal cavities in basalts and related rocks. Found associated with other zeolites, calcite, etc.  notable localities for its occurrence are Poonah, India Isle of Skye; Faroe Island; Kilpatrick, Scotland; Ice land; northeastern New Jersey; Nova Scotia.

Name. derived from a Greek word meaning luster.