Clinoptilolite is a natural zeolite composed of a microporous arrangement of silica and alumina tetrahedra. It has the complex formula: (Na 3(Al,Si 2O. It forms as white, green to reddish tabular monoclinic crystals with a Mohs hardness of 3.5 to 4 and a specific gravity of 2.1 to 2.2. It commonly occurs as a devitrification glass shards in tuff , andesites. It was described in 1969 from an occurrence in the Barstow Formation, San Bernardino County. Sodium levels in clinoptilolite are generally higher than potassium levels, as is the case with the San Bernardino Barstow Formation, but there are sources that are potassium-rich and have minimal sodium.
It forms a series with heulandite : * Clinoptilolite-Ca – heulandite-Ca solid solution series * Clinoptilolite-K – heulandite-K solid solution series * Clinoptilolite-Na – heulandite-Na solid solution series
Use of clinoptilolite in industry and academia focuses on its ion exchange properties having a strong exchange affinity for ammonium H4+). A typical example of this is in its use as an enzyme
Research is generally focused around the shores of the Aegean Sea due to the abundance of natural clinoptilolite in easily accessible surface deposits.
The name is derived from the Greek words klino (κλίνω; "oblique"), ptylon (φτερών; "feather"), and lithos (λίθος; "stone").
United States sources of clinoptilolite are found in California, Idaho, New Mexico, Oregon, and Texas deposits.