NATROLITE
Natrolite is a sodium zeolite with the formula Na2Al2Si3O10·2H2O
- hydrous sodium aluminosilicate. It has the same general physical
properties as scolecite (calcium zeolite): glassy, nonmetallic luster, variably
colored, white streak, moderately hard (H = 5 to 5.5), and tends to form
radiating masses of long, needle-like crystals (see 2nd photo below).
The first natrolite sample shown below has been
acid-etched. It forms part of a multimineralic vein intruding
blueschist. The natrolite has been mostly dissolved away to expose the
other, non-acid soluble minerals of the vein.
Natrolite (white) on blueschist (glaucophane metamorphite), associated with
neptunite (black) and joaquinite (orangish-brown).
Field of view 15 mm across.
Natrolite from San Juan, Argentina. (Dwyer Mercer County District Library
collection, Celina, Ohio, USA)