Natrolite

Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate.

It named natrolite by Martin Heinrich Klaproth in 1803. The name derived from natron, the Greek word for soda, in reference to the sodium content, and lithos, meaning stone. Needle stone or needle-zeolite are other informal names, alluding to the common acicular habit of the crystals, which often very slender and aggregated in divergent tufts. The crystals are frequently epitaxial overgrowths of natrolite, mesolite, and gonnardite in various orders.

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 decomposed by hydrochloric acid with separation of gelatinous silica.