Clinoptilolite-Ca: Ca3(Si30Al6)O72.20H2O
Clinoptilolite-K: K6(Si30Al6)O72.20H2O
Clinoptilolite-Na: Na6(Si30Al6)O72.20H2O

All are tectosilicates (framework silicates), zeolite group
Specific gravity: 2.1 to 2.2
Hardness: 3½ to 4
Streak: White
Colour: White, Reddish white, red

Volcanic igneous environments
Basaltic cavities

Clinoptilolite is most commonly formed as a devitrification product of silicic volcanic glass from tuff. It also occurs in cavities in rhyolite, andesite, and basalt. Associated minerals include other zeolites, montmorillonite, hectorite, thénardite, halite, gaylussite, celadonite, quartz, opal and calcite (Dana, HOM).
Clinoptilolite is very similar to heulandite, but the response to temperature is different for the two minerals; clinoptilolite has a high heat resistance such that heating at 750oC does not normally destroy the lattice, whereas the heulandite lattice is destroyed at a much lower temperature of about 550oC (AM 57.1448-1462).


At the Cañadón Hondo, Neuquén Province, Argentina, clinoptilolite occurs as a layer 6-8 cm thick interbedded with bentonitic clay. A specimen has been found with one surface coated with a 1 mm layer of baryte. The clinoptilolite apparently was formed by the alteration of fine-grained volcanic glass; it has rare thin veinlets of opal and montmorillonite. The bentonitic clay consists essentially of montmorillonite (AM 45.341-345).

At the Hector Bentonite Mine No. 1, Hector, Cady Mountains, San Bernardino county, California, USA, clinoptiloloite has been found in beds of altered pyroclastic material, closely associated with montmorillonite and hectorite (AM 45.351-369).

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