What is Natrolite?
Natrolite is a white fibrous zeolite famous for needle sprays in volcanic cavities and for its open framework that exchanges water and ions.
Mineralogy and crystal structure
Reference formula: Na2Al2Si3O10·2H2O. Natrolite is an orthorhombic zeolite with a channelled framework. It commonly grows with mesolite, scolecite and analcime, and the fine radiating habit is more diagnostic than colour alone. Natrolite is classified with silicates and has a orthorhombic crystal system. Typical hardness is 5–5.5 on the Mohs scale and specific gravity is approximately 2.2–2.3.
Colour, lustre and habit
Typical colours include white, colourless, pink, yellow. The usual needle-like, fibrous, radiating habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Natrolite forms in or is associated with basalt cavities, alkaline volcanic rocks and low-temperature hydrothermal veins. Important documented localities include India, Germany, Scotland, Iceland, Canada, Russia and the United States.
A white zeolite spray on dark basalt
Natrolite makes a volcanic cavity look architectural: fine needles radiate into open space while the framework records water movement through cooling lava.
Collecting and care
Protect fine needles from vibration and cleaning; keep dry and supported.
