Prehnite Composition, Crystallization & Structure
Composition. H2Ca2Al.2Si3O12 = Silica 43.7, alumina 24.8, lime 27.1, water 4.4.
Crystallization. Orthorhombic. Distinct crystals rare.
Structure. Reniform, stalactites. In rounded groups of tabular crystals.
Physical Properties. H. = 6-6.5. G. = 2.8-2.95. Vitreous luster. Color usually light green, passing into white. Translucent.
Tests. Fuses at 2.5 with intumescence to an enamel. Heated in C. T. yields water. Slowly acted upon by, hydrochloric acid but gelatinizes after simple fusion.
Occurrence. As a mineral of secondary origin lining amygdaloidal cavities in basalt, etc. Associated with zeolites, datolite, pectolite, calcite, ete. Occurs in the United States at Farrmington, Connecticut; Paterson and Bergen Hill, New Jersey; Somerville, Massachusetts; Lake Superior copper district. Found also in various European localities.
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