natrolite Member of the zeolite group of minerals, with the formula Na₂Al₂Si₃O_10.2H₂O; sp. gr. 2.2; hardness 5.0; white; massive, fibrous, or crystalline; occurs as a secondary mineral infilling cavities in basic volcanic rocks and as an alteration product of nepheline.

natrolite (Na₂Al₂Si₃O₁₀.2H₂O) Hydrated silicate mineral, hydrous sodium aluminium silicate. It has orthorhombic system, needle-like crystals, with radiating nodules or compact fibrous masses. It is colourless or white, glassy and brittle. Hardness 5–5.5; r.d. 2.2. See also zeolite