Everything about Natrolite totally explained
Natrolite is a
tectosilicate mineral species belonging to the
zeolite group. It is a hydrated
sodium and
aluminium silicate with the formula .
It was named natrolite by
Martin Heinrich Klaproth in 1803. Needle stone or needle-zeolite are other names, alluding to the common acicular habit of the
crystals, which are often very slender and are aggregated in divergent tufts. Larger crystals 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 don't 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 is 2.2, and the
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.
Natrolite occurs with other zeolites in the amygdaloidal cavities of
basaltic
igneous rocks. The best specimens are the diverging groups of white prismatic crystals found in compact
basalt at the Puy-deMarman, Puy-de Dome,
France. The largest crystals are those from Brevig in
Norway. The walls of cavities in the basalt of the
Giants Causeway, in Co. Antrim, are frequently encrusted with slender needles of natrolite, and similar material is found abundantly in the volcanic rocks (basalt and
phonolite) of Salesel, Aussig and several other places in the north of
Bohemia.
Several varieties of natrolite have been distinguished by special names.
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.
Further Information
Get more info on 'Natrolite'.
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