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An example of the mineral formula of a zeolite is: Na 2 Al 2 Si 3 O 10 ·2H 2 O, the formula for natrolite. Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater. Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins.
Clinoptilolite is a natural zeolite composed of a microporous arrangement of silica and alumina tetrahedra. It has the complex formula (Na,K,Ca) 2–3 Al 3 (Al,Si) 2 Si 13 O 36 •12H 2 O. It forms as white, green to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5 to 4 and a specific gravity of 2.1 to 2.2.
Faujasite (FAU-type zeolite) is a mineral group in the zeolite family of silicate minerals.The group consists of faujasite-Na, faujasite-Mg and faujasite-Ca. They all share the same basic formula (Na 2,Ca,Mg) 3.5 [Al 7 Si 17 O 48]·32(H 2 O) by varying the amounts of sodium, magnesium and calcium. [1]
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula Na 2 Al 2 Si 3 O 10 ·2H 2 O. [4] The type locality is Hohentwiel, Hegau, Germany. [3] It was named natrolite by Martin Heinrich Klaproth in 1803. [3]
The ferrierite group of zeolite minerals (the FER structure) consists of four very similar species: ferrierite-Mg, ferrierite-Na, ferrierite-NH4 and ferrierite-K, based on the dominant cation in the A location. ferrierite-Mg and ferrierite-K are orthorhombic minerals and ferrierite-Na is monoclinic with highly variable cationic composition (Na,K) 2 Mg(Si,Al) 18 O 36 (OH)·9H 2 O.
Isomorphous with heulandite is the strontium and barium zeolite brewsterite. The Mohs hardness is 3–4, and the specific gravity 2.2. Heulandite is similar to stilbite. The two minerals may, however, be readily distinguished by the fact that in heulandite the acute positive bisectrix of the optic axes emerges perpendicular to the cleavage. [6]
Phillipsite is a mineral of secondary origin, and occurs with other zeolites in the amygdaloidal cavities of mafic volcanic rocks: for example in the basalt of the Giants Causeway in County Antrim, and near Melbourne in Victoria; and in Lencitite near Rome.
Wairakite is a zeolite mineral with an analcime structure but containing a calcium ion. The chemical composition is Ca 8 (Al 16 Si 32 O 96)•16H 2 O. It is named for the location of its discovery in Wairakei, North Island, New Zealand, by Czechoslovakian mineralogist Alfred Steiner in 1955.