Natrolite

Larger crystals most commonly have the form of a square prism terminated by a low pyramid, the prism angle being nearly a right angle. The crystals are tetragonal in appearance, though actually orthorhombic. There are perfect cleavages parallel to the faces of the prism. The mineral also often occurs in compact fibrous aggregates, the fibers having a divergent or radial arrangement. Natrolite is readily distinguished from other fibrous zeolites by its optical characteristics. Between crossed nicols the fibers extinguish parallel to their length, and they do not show an optic figure in convergent polarized light. Natrolite is usually white or colorless, but sometimes reddish or yellowish. The luster is vitreous, or, in finely fibrous specimens, silky. The specific gravity of natrolite is 2.2, and its hardness is 5.5. The mineral is readily fusible, melting in a candle-flame to which it imparts a yellow color owing to the presence of sodium. It is decomposed by hydrochloric acid with separation of gelatinous silica. == Environment ==

Natrolite occurs with other zeolites in the amygdaloidal cavities of basaltic igneous rocks. It is also common in nepheline syenites. == Notable localities ==

Excellent specimens of diverging groups of white prismatic crystals are found in compact basalt at the Puy-deMarman, Puy-de-Dôme, France. Huge crystals have been found on the Kola Peninsula, Russia (30 cm by 13 cm). The Bay of Fundy in Nova Scotia, New Jersey, Oregon, and British Columbia have also produced excellent specimens. Several varieties of natrolite have been distinguished: fargite is a red natrolite from Glenfarg in Perthshire; bergmannite or spreustein is an impure variety which has resulted by the alteration of other minerals, chiefly sodalite, in the augite syenite of southern Norway. Natrolite is one of the closely associated minerals with benitoite, a rare mineral with its type locality in San Benito County, California. Natrolite forms opaque white spherical inclusions within nodules of translucent green prehnite from Wave Hill, Northern Territory, Australia. ==Images==

File:Phonolith.JPG|Natrolite from Hohentwiel (Hegau) File:Natrolith Aussig.JPG|Natrolite from Aussig. File:Zeolite-greenland hg.jpg|Natrolite from the plateau basalts in east Greenland File:Natrolite-61051.jpg|Colorless, radiating natrolite in zeolite pod File:Catapleiite, Natrolite-168971.jpg|Catapleiite and natrolite from Poudrette quarry, Québec, Canada File:Natrolite-Inesite-21148.jpg|Slender needles of natrolite are accented by deep pink inesites File:Natrolite-223955.jpg|Natrolite in spherical clusters inside protective pocket of volcanic rock File:Natrolite-Inesite-37029.jpg|Natrolite sprays of stark white crystals are shooting out from a vug of inesite == See also ==