Silicates: Chabazite

Composition: CaAl₂Si₄O₁₂.6H₂O; sodium and potassium may replace calcium

Crystal system: Trigonal; crystals rhombohedral but resemble cubes, also massive

5.7.1
apophyllite crystals and chabazite on basalt
Poona India

Properties:

• Vitreous lustre
• Colorless or white color; sometimes cream to pink
• White streak
• Knife barely scratches (Mohs Hardness 5)
• Below average density
• Cleavage rarely apparent
• Uneven fracture
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

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

5.7.2
apophyllite crystals and chabazite on basalt
Poona India

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