Silicates: Laumontite

Composition: CaAl₂Si₄O₁₂.4H₂O; sodium and potassium may replace calcium

Crystal system: Monoclinic; stout prismatic crystals, also massive

5.16.1
zeolites with basalt

Properties:

• Vitreous lustre
• White color
• White streak
• Knife scratches easily (Mohs Hardness 4)
• Below average density
• Two cleavages apparent if not finegrained
• Cleaves rather than fractures
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Zeolites including laumontite occur most commonly in veins and cavities in basalts and also form by the alteration of tuffaceous sediments. The crystal form and good cleavage are diagnostic for laumontite; however, specialised characterisation may be required to distinguish the zeolite varieties.

5.16.2 zeolites with basalt	5.16.3 zeolites with basalt

5.16.4 zeolites with basalt	5.16.5 zeolites with basalt

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