Silicates: Natrolite

Composition: Na₂Al₂Si₃O₁₀.2H₂O

Crystal system: Orthorhombic; needle-like crystals, also in radiating and compact masses

5.17.1
natrolite needles
Milbong Qld Australia

Properties:

• Vitreous lustre
• Colorless or white color
• White streak
• Knife barely scratches (Mohs Hardness 5)
• Below average density
• Cleavage sometimes apparent
• May cleave rather than fracture if coarsegrained
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Zeolites including natrolite occur most commonly in veins and cavities in basalts and also form by the alteration of tuffaceous sediments. The needle-like form of natrolite is diagnostic; however, specialised characterisation may be required to distinguish the zeolite varieties.

5.17.2
natrolite needles
Milbong Qld Australia

Zeolites are important industrial minerals used mainly in the separation or purification of gases and liquids.