Silicates: Heulandite

Composition: CaAl₂Si₇O₁₈.6H₂O; sodium and potassium may replace calcium

Crystal system: Monoclinic; tabular crystals, also massive

5.12.1
heulandite crystals

Properties:

• Vitreous to silky lustre
• White color; sometimes reddish
• White streak
• Knife scratches very easily; fingernail does not scratch (Mohs Hardness 3-4)
• Below average density
• One cleavage apparent if not finegrained
• Cleaves rather than fractures
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

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

5.12.2 heulandite crystals	5.12.3 heulandite crystals

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

5.12.4
heulandite crystals