Zeolites, Heulandite Phillipsite and Harmotone Composition & Structure

Zeolites
The zeolites from a large family of hydrous silicates which show close similarities in composition and in their associations and mode of occurrence. They are silicates of aluminum with sodium and calcium as the important base. They average from 3.5 to 5.5. in hardness and from 2 to 2.4 in specific gravity. Many of them fuse readily with marked intumescence, hence the name zeolite, from two Greek words meaning to bail and stone. They are secondary minerals found characteristically in cavities and veins in basic igneous rocks.

Heulandite
Composition. H₄CaAl₂(SiO₃)₆.₃H₂O. Monoclinic, but crystals often simulate orthorhombic symmetry. Clinopinacoid prominent, having often a diamond shape. Perfect cleavage parallel to clinopinacoid. H. = 3,5-4. G. = 2.15-2.2. Vitreous luster, except on clinopinacoid, which is pearly. Color white, yellow, red. Transparent to almost opaque. Fusible (3) with inturnescence. Decomposed by hydrochloric acid with separation of silica. Water in C. T. A mineral of secondary origin found usually in cavities of basic igneous rocks associated with other zeolites, calcite, ete. Found in innotable quality in Iceland; the Faroe Islands; Andreasberg, Harz Mts.; Tyrol, Austria; British India, near Bombay¡ West Paterson, ete., New Jersey; Nova Scotia.

Phillipsite
Composition, (K₂,Ca)Al₂Si₄O₁₂.41/2H₂O. Monoclinic. Crystals are uniformly penetration twins but often appearing to be tetragonal or orthorhombic in form. Cleavage parallel to base and clinopinacoid. H. = 4-4.5. G. = 2.2. Vitreous luster. White or reddish in color. Translucent to opaque. Fuses at 3 to a white enamel. Gelatinizes with hydrochloric acid. Water in C. T. A secondary mineral found in cavities of igneous rocks associated with other zeolites, ete.

Harmotone
A barium zeolite having the composition (K2,Ba)AI2Si4012.3H2O. Monoclinic. Crystals are uniformly cruciform penetration twins. Perfect cleavage parallel to clinopinacoid. H. = 4.5. G. = 2.42.5. Vitreous luster. Colorless or white. Translucent. Fuses at 3. Decomposed by hydrochloric acid with separation of silica. Addition of sulfurie acid to hydrochloric acid solution gives a white precipitate o barium sulphate. Water in C. T.

A mineral of secondary origin, occurring in cavities of basic igneous roeks, associated with other zeolites, calcite, ete.