Natrolite is a hydrated silicate mineral, hydrous sodium aluminium silicate (Na₂A1₂Si₃O₁₀.2H₂O). It has orthorhombic system, needle-like crystals, with radiating nodules or compact fibrous masses. Natrolite is colorless or white, glassy and brittle. Hardness 5–5.5; relative density 2.2.