All are tectosilicates (framework silicates), zeolite group
Specific gravity: 2.1 to 2.2
Hardness: 3½ to 4
Colour: White, Reddish white, red
Volcanic igneous environments
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,
quartz, opal and
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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