Clinoptilolite-K |(K,Na,Ca_0.5,Sr_0.5,Ba_0.5,Mg_0.5)₆(H₂O)₂₀|[Al₆ Si₃₀ O₇₂]
Clinoptilolite-Na  |(Na,K,Ca_0.5,Sr_0.5,Ba_0.5,Mg_0.5)₆(H₂O)₂₀|[Al₆ Si₃₀ O₇₂]
Clinoptilolite-Ca  |( Ca_0.5,Na,K, Sr_0.5,Ba_0.5,Mg_0.5)₆(H₂O)₂₀|[Al₆ Si₃₀ O₇₂]

Cleavage: {010} perfect.
Hardness: 3.5 - 4
D: 2.14 - 2.17 gm/cm³.
Luster: vitreous, pearly on {010}. Streak: white.

Biaxial (+ or -), 

α 1.476 - 1.478,  β 1.477 -  1.479  , γ  1.479 - 1.481  , δ 0.003,  2Vz  58 - 73°,  Y = b, Z ∧ c  38° - 58°  (or Z = b).
Dispersion: r  > v, distinct,  crossed

α 1.474 - 1.478,  β 1.475 -  1.479,  γ 1.478 - 1.481, δ 0.003 - 0.004,
2Vz 32 - 95°, X = b, Z ∧ 18° - 23° (or Z = b). 
Dispersion: r > v, moderate

α 1.481,  β 1.484,  γ 1.488, δ 0.007, 2Vz 70°, Z = b, X ∧ c  20°. 
Dispersion: r < v, distinct

a  17.688(16),  b  17.902(9),  c  7.409 (7) Å, β  116.50(7)°.
Z = 1,  Space group C2/m, C2, or Cm.
(Ogihara and Iijima 1990, off-shore borehole, Japan)

a  17.627(4),  b  17.955(4),  c  7.399(4) Å, β  116.29(2)°.
Z = 1,  Space group C2/m, C2, or Cm.
(Sheppard and Gude 1969, Barstow Formation, San Bernardino County, California, USA)

a  17.660(4),  b  17.963(5),  c  7.400(3) Å, β  116.47(3)°.
Z = 1,  Space group C2/m, C2, or Cm.
(Koyama and Takeuchi 1977, Kuruma Pass, Fukushima Prefecture, Japan)

The origin and use of the name clinoptilolite has a convoluted history. The type locality is
on the ridge trending several kilometers northeast of Hoodoo Peak just outside the eastern boundary of Yellowstone National Park, Park County, Wyoming, USA, where the mineral occurs cavities of decomposed basalt breccia. The crystals were first identified by Pirsson (1890) as mordenite, based solely on chemical analysis. The platy habit and optical properties led Schaller (1923, 1932) to conclude that it was a monoclinic dimorph of ptilolite, a finely fibrous mineral described and named by Cross and Eakins (1886) for material occurring at Table Mountain, Colorado, USA and later shown to be mordenite. Schaller, therefore, named these crystals clinoptilolite, even though the morphology was very similar to heulandite. Based on X-ray diffraction data Hey and Bannister (1934) determined that the Hoodoo Peak material and heulandite are isostructural and recommended that the term clinoptilolite not be used.

Mason and Sand (1960) proposed a new definition for clinoptilolite, based on alkali-dominant and high Si/Al compositions. Mumpton (1960) simultaneously suggested that the name be applied to those samples that remained stable following overnight heating to 350°C. This method works particularly well for the fine-grained replacements of vitric tuff. During the following years the compositional gap observed by Mason and Sand (1960) was filled by the analysis of many newly discovered samples. Even so, the subcommittee reviewing the nomenclature of the zeolite group (Coombs et al. 1997) chose to retain the two mineral names, and proposed to keep both the heulandite and clinoptilolite names and to separate them based on the framework composition at Si/Al = 4.0. For a discussion of this nomenclature problem and some guidance in distinguishing between heulandite and clinoptilolite, see Bish and Boak (2001).

Both names were also raised to series status to include several species based on the dominant cation content. The clinoptilolite series comprises three species. Clinoptilolite-K is the new name for the original material from the ridge east of Hoodoo Peak, Wyoming. Clinoptilolite-Nais a new name for Na dominant crystals with the suggested type example from the Barstow formation, San Bernardino County, California, USA, and clinoptilolite-Cafor Ca dominant samples with type examples from Kuruma Pass, Fukushima Prefecture, Japan.

Both clinoptilolite and heulandite possess the same tetrahedral framework (labeled HEU) and form a continuous compositional series sometimes referred to as the heulandite group zeolites. The crystal structures of clinoptilolite and heulandite are mostly described to be monoclinic, space group C2/m (e.g. Alberti 1975, Koyama and Takeuchi 1977, Bresciani-Pahor et al. 1980, Alberti and Vezzalini 1983, Hambley and Taylor 1984, Smyth et al. 1990, Armbruster and Gunter 1991, Armbruster 1993, Gunter et al. 1994, Cappelletti et al. 1999). However, lower symmetries such as Cm and C1 have also been reported (Alberti 1972, Merkle and Slaughter 1968, Gunter et al. 1994, Yang and Armbruster 1996, Sani et al. 1999, Stolz et al. 2000a). The HEU framework contains three sets of intersecting channels all located in the (010) plane. Two of the channels are parallel to the c-axis: the A channels are formed by strongly compressed ten-membered rings (aperture 3.0 x 7.6 Å ) and B channels are confined by eight-membered rings (aperture 3.3 x 4.6 Å). C channels are parallel to the a-axis, or [102] and are also formed by eight-membered rings (aperture 2.6 x 4.7 Å).

Alberti (1972) concluded that the true probable lower symmetry of heulandite cannot reliably be extracted from X-ray single crystal data because of strong correlations of C2/m pseudo-symmetry related sites during the least-squares procedure. Thus C1, C1, Cm, C2, C2/m are possible space groups for clinoptilolite and heulandite. Akizuki et al. (1999) determined by optical methods and X-ray diffraction that a macroscopic heulandite crystal is composed of growth sectors displaying triclinic and monoclinic symmetry where the triclinic sectors are explained by (Si,Al) ordering on the crystal faces. Yang and Armbruster (1996) and Stolz et al. (2000a,b) stated that, owing to correlation problems, symmetry lowering in heulandite can only be resolved from X-ray data when investigated in cation-exchanged samples where the distribution of non-framework cations also reflects the lower symmetry.

Differing degrees of (Si,Al) ordering over the five distinct tetrahedral sites (assuming C2/m space group) have been reported for both heulandite and clinoptilolite. In all refinements, the tetrahedron with the highest Al content, T2, joins the "sheets" of T₁₀O₂₀ groups by sharing their apical oxygens. A neutron diffraction study by Hambley and Taylor (1984) located the majority of the H atoms and found (Si,Al) ordering values similar to other C2/m refinements. Additional (Si,Al) ordering, due to lower symmetry (C1  or Cm), was resolved by Yang and Armbruster (1996), Sani et al. 1999, and Stolz et al. (2000a,b).
Two main channel cation sites have been reported by all researchers and at least two more sites of lower occupancy have been reported by others (e.g. Sugiyama and Takeuchi 1986, Armbruster and Gunter 1991, Armbruster 1993). These sites commonly contain Na, Ca, K, and Mg, with Na and K predominantly close to the intersection of the A and C channels and Ca located in the B channel. The Na site in the A channel generally also contains Ca, whereas the Ca site in the B channel is mostly Na free. K and Na occur in nearby sites, but K is more centered in the C channel. Both can be distinguished by their different distances from the framework. Na, K, and Ca ions are on the (010) mirror plane, present in the C2/m or Cm symmetry, and they coordinate to framework oxygens and channel H₂O molecules. In one refinement, Na was nine-coordinated to four framework oxygens and five strongly disordered and partially occupied H₂O molecules, whereas both Ca and K were eight-coordinated to four framework oxygens and four channel H₂O molecules (Gunter et al. 1994). Mg commonly resides in the center of the A channel, coordinated only to six disordered H₂O
molecules (Koyama and Takeuchi 1977, Sugiyama and Takeuchi 1986, Armbruster 1993).

Clinoptilolite and heulandite contain differing amounts of H₂O as a function of their non-framework cation chemistry (Bish 1988, Yang and Armbruster 1996) and hydration state. The H₂O molecules occurring in the B channel (coordinated to Ca) are commonly fully occupied, whereas those occurring in the A channel are generally only partially occupied (Koyama and Takeuchi 1977, Armbruster and Gunter 1991). The structural mechanism of dehydration and accompanying framework distortion were studied by Alberti (1973), Alberti and Vezzalini (1983), Armbruster and Gunter (1991), and Armbruster (1993). When compressing in water medium, clinoptilolite is subjected to pressure-induced hydration with persistent increasing of H2O content over a wide pressure range. This occurs owing to the additional population of partially vacant positions (Seryotkin 2015; Strzelecki et al. 2022).

Clinoptilolite series minerals are by far the most common zeolites. These minerals occur in rocks and sediment seemingly formed in widely disparate environments, which include deep sea sediment, continental accumulations in thick basin fills and in shallow lakes, and in some lava flow sections. The following summary is adapted and updated from Bish and Ming (2001), Deer et al. (2004), and the Commission on Natural Zeolite (IZA) website.

Diagenesis of sediment and sedimentary rocks.
Minerals of the clinoptilolite series occur in diverse, low temperature environments, mostly, but not exclusively, as a result of alteration of volcanic rocks and fragmental debris (Hay and Sheppard 2001, Utada 2001a). This alteration occurs as a reaction between volcanic glass and interstitial solutions during diagenesis. The composition of the clinoptilolite zeolite is dependent on the compositions of the glass and of the solution. Clinoptilolite series minerals commonly replace high silica rocks, those ranging from andesite to rhyolite. Because of their size, and hence of economic importance, the replacement of ignimbrite sheets (welded pyroclastic flow deposits) that may occur in shallow marine environments and in terrestrial basins are of particular importance.

Diagenesis of marine pyroclastic and volcaniclastic sequences. Aleksiev and Djourova (1975) and Yanev et al. (2006) show that Paleogene volcanism occurring in the northeast Rhodope Mountains of southern Bulgaria, produced extensive deposits of sub-aqueous pyroclastic flows, fall-out tuff, and volcaniclastic sands all of which accumulated in a shallow marine basin. Irregular replacement of these deposits suggests that suitable conditions for the growth of zeolite minerals were controlled by local geology and fluid sources. Zeolitic alteration occurred from solutions consisting of marine water heated by the anomalous geothermal gradient of the active volcanic areas or/and by the hot pyroclastic rocks. Although individual units are incompletely exposed, composite vertical sections have the generalized vertical diagenetic mineral zoning: analcime, clinoptilolite-Na, clinoptilolite-Ca, clinoptilolite-K, and uppermost unaltered glass. In Cuba, zeolite deposits are hosted in Cretaceous and Paleogene volcanic arcs, and in overlapping basins of both arcs. Most of the occurrences contain clinoptilolite and mordenite in different proportions, but in the Eastern region, the Paleogene deposits are mainly mordenite (Brito-Rojas et al. 2017).

The Castilla, Tasajeras, Las Pulgas, and Caimanes clinoptilolite deposits in the Western region are of this type (Gonzalez et al. 1991).

Diagenesis in hydrologically closed systems. In general alteration in hydrologically closed systems occurs where the glass particles of fall-out tuff react with interstitial lake water, incorporated at the time of deposition. For a zeolite mineral to be produced, this water must have high salinity and high pH, usually higher than those of sea water. This situation can occur where rhyolitic ash falls into saline and alkaline lakes that form in arid environments (Langella et al. 2001). Replacement of vitric tuff in hydrologically closed systems tends to produce beds of nearly pure zeolite that have substantial economic value. Tuff beds replaced by this mechanism have a characteristic lateral variation from unaltered glass at the lake margin through an intermediate zeolite zone to a potassium feldspar zone near the lake center. This type of alteration process was recognized early by Hay (1966), but the clear relationships at the Pleistocene Lake Tecopa, Inyo County, California, USA, (Sheppard and Gude 1968), provide the conceptual basis upon which other occurrences are compared.

The exposed lake deposits of Lake Tecopa cover an area of about 230 km² and consist of 67 m of mudstone with interlayered vitric, rhyolitic tuff, comprising 8 to 12 percent of the section (Sheppard and Gude 1968). Tuff beds range in thickness from 4 cm to 4 m. Post Pleistocene erosion has exposed the lake beds in Badlands-type landform, and several individual tuff beds can be traced throughout the basin. Tuff near the lake margins consists almost entirely of unaltered rhyolitic glass, and in the center of the lake they are replaced by potassium feldspar, locally associated with searlesite (NaBSi₂O₅(OH)₂). There are scattered occurrences of saline minerals (trona and possibly gaylussite) within the K-feldspar area. Between these areas is the zeolite zone, in which the authigenic minerals are phillipsite-Na, clinoptilolite-Na, erionite-Na, and analcime, in order of abundance.

Similar deposits containing clinoptilolite in the western U.S. include the Pliocene Big Sandy Formation in Mohave County, Arizona, (Sheppard and Gude, 1973); the Miocene Barstow Formation, exposed in the Mud Hills, San Bernardino County, California (Sheppard and Gude 1969); zeolitic tuff in a lacustrine facies of the Gila Conglomerate (Pliocene?) near Buckhorn, Grant County, New Mexico, (Gude and Sheppard 1988); the Pliocene to Holocene lacustrine, Bowie zeolite deposit Cochise and Graham Counties, Arizona (Sheppard et al. 1978); and the huge lake deposits in the Jurassic Morrison Formation, eastern Colorado Plateau (Turner and Fishman 1991).

Clinoptilolite, erionite, and chabazite replace vitric clasts in rhyolitic pyroclastic beds of the Baucarit Formation of Sonora, Mexico (Cocheme et al. 1996, Munch et al. 1996). Farther south in the Sierra Madre Occidental late Miocene volcanism resulted in the accumulation of large deposits of pyroclastic rocks. Some were deposited in closed basins and shallow marine environments, and were diagenetically altered to zeolites, including clinoptilolite (de Pablo-Galan et al. (1996).

Many closed basins, formed by extensional tectonics during the Tertiary in Anatolia, Turkey, had lakes that were saline and alkaline. Contemporaneous volcanic activity contributed pyroclastic and volcaniclastic material to the lake deposits, which in some include lignite or borate beds. Gundogdu et al. (1996) describe the geology and mineralogy of lacustrine deposits containing borate deposits in western Turkey. Beds in the Bigadic, Emet, and Kirka basins include thick sequences of tuff that have been replaced by clinoptilolite-K, which locally has been replaced by analcime, potassium feldspar, and quartz. Analcime and clinoptilolite comprise up to 80% of the mineral matter in coal from the Cayirhan mine, Beypazari, western Turkey (Whateley et al. 1996). Much of this zeolite also occurs as replacement of vitric tuff, caused by reaction with saline and alkaline lake water. In most cases clinoptilolite and analcime replace the vitric component of tuff with relationships similar to those deposits in the western U.S.

Tertiary lacustrine deposits are widespread in Serbia (Obradovic et al. 1995, Obradovic 1988, Gottardi and Obradovic 1978). Tectonic activity developed closed basins, which became the sites of shallow lakes. The lacustrine sediment is largely tuff and volcaniclastic sand and silt accompanied with marl. The volcanic debris, which ranges from rhyodacite to andesite, is replaced by zeolites, commonly clinoptilolite and analcime. In the Slanci basin near Belgrade authigenic minerals are horizontally zoned from fresh glass to montmorillonite to clinoptilolite to analcime (Obradovic 1988). At the base of the section is unaltered sediment from when the early lake was filled with fresh water, and later with a change in climate and lake depth it became sufficiently saline and alkaline to alter the vitric tuff.

Soil and surficial deposits. Clinoptilolite is the most common zeolite occurring in soils, especially those developed from zeolite-bearing parent materials (Ming and Boettinger 2001). Reported occurrences are in the U.S., eastern Europe, Lebanon, and Japan.

Clinoptilolite is widespread in calcareous soils developed on tuffaceous sediment. For example, it is widespread in soils formed on the Catahoula Formation of south Texas (Ming and Dixon 1986) and on volcanic-rich parent units in west Texas (Jacob and Allen 1990). Other occurrences in the U.S. and elsewhere, including Hungry, Bulgaria, Romania, Lebanon, India, and Japan are briefly described by Ming and Boettinger (2001).

Brown et al. (1969) found clinoptilolite or heulandite in soils developed from calcareous, fine-grained siliceous rocks of the Upper Greensand Formation of England. The zeolite may be a diagenetic product from biogenic opal, and was inherited by the soil. A similar occurrence of clinoptilolite was described in calcareous soils of Sicily (Bellanca et al. 1980) and of heulandite in soils developed from the byrozoan chalk in northeastern Denmark (Nornberg 1990).

Hydrologically open systems. Replacement of rhyolitic pyroclastic rocks in hydrologically open systems generally occurs where pyroclastic deposits have accumulated several hundred meters in thickness and tens of kilometers in lateral extent. Alteration occurs by meteoric water percolating through the deposit, first hydrating glass shards, and deeper into the pile commonly at the water table dissolve glass shards and crystallizing zeolite, mostly clinoptilolite. The authigenic minerals tend to be zoned vertically with slightly altered glass and smectite upper most, clinoptilolite and smectite in a middle layer, and commonly potassium feldspar and analcime with smectite/illite at the base. A common consequence of the hydrologically open system type of replacement is the change in bulk composition by leaching of upper levels and precipitation in lower levels. By contrast replacement processes in hydrologically closed systems produce lateral variations in authigenic mineralogy accompanied by little bulk composition change.

The first well described deposit of the hydrologically open type is the John Day Formation of central Oregon, USA. (Hay 1963). The Oligocene John Day Formation consists of 700 to 1000 m of rhyolitic and dacitic tuff and welded tuff, exposed over an area of at least 5000 km². In the thicker parts of the formation the upper 500 m contains glass, smectite, and opal, but no zeolite. Clinoptilolite, smectite, and celadonite are abundant in the lower 500 m. Other authigenic minerals include erionite, mordenite, heulandite, and K-feldspar. The contact between the upper and lower parts tends to be planar and cuts across stratification. Hay (1963) describes this boundary as being a cavernous zone 2 to 20 mm thick with many of the vitric particles having been dissolved away. The replacement of glass shards apparently occurs by dissolution of the glass and followed by precipitation of clinoptilolite. K/Ar dates on authigenic K-feldspar deep in the section indicates that most authigenic reactions had occurred by early Miocene, before deposition of the top of the section had been completed.

Another well investigated example of the alteration of a thick pile of pyroclastic rocks is Yucca Mountain along the southwest edge of the Nevada Test Site in Nye County, Nevada, USA. Here a thick sequence of Miocene pyroclastic flow tuff, and lesser amounts of flow breccia, lava, and tuff, has accumulated in a basin at least 1800 m thick in the center and thinning to about 1200 m to the east. These products erupted from the nearby Timber Mountain-Oasis Valley caldera complex to the north. Because a large block of these rocks is being considered as a repository for radioactive waste, the mountain has been extensively drilled, and the cores studied in detail. Broxton et al. (1987) divide the diagenetic alteration into four mineral zones. Zone 1 is the upper most 375-384 m that consists of unaltered glass with minor smectite, opal and scattered occurrences of heulandite-Ca and clinoptilolite-Ca. In Zone 2, the next 700 to 480 m in depth, the main alteration mineral is clinoptilolite with minor mordenite and lesser amounts of opal, K-feldspar, quartz, and smectite. Zone 3, 400 to 98 m thick, consists of analcime, K-feldspar, and minor calcite and smectite. Zone 4, at the deepest levels, typically has authigenic albite, K-feldspar, and quartz. All zones thin toward the north, the direction of the caldera complex.

The White River sequence, described by Lander and Hay (1993), is an extensive formation largely a non-lacustrine accumulation of rhyolitic tuffs and reworked ash and exposed in Wyoming, South Dakota, and Nebraska, USA. The glass has been altered to smectite, opal-CT, and clinoptilolite. Smectite is abundant throughout the formation, but the distribution of opal-CT and clinoptilolite is variable.

Petrova et al. (1987) describe zeolite occurrences at Tushleg and Tsagan-Tsab in southern Mongolia. The upper Jurassic and lower Cretaceous sections consist of 85 to 110 m of tuffaceous sandstone, siltstone, peat-bearing siltstone, and conglomerate with fresh water fossils (fish, insects, and ostracods). Other large deposits occur in Siberia.

Flood and Taylor (1991) and Flood (1995) describe two provinces in eastern Australia in which Carboniferous marine volcaniclastic deposits contain abundant clinoptilolite. The New England province (Early Carboniferous) consists largely of non-marine silicic ignimbrite and tuff units interbedded with fluvial and glacio-fluvial conglomerate, sandstone, and mudstone. Most of the zeolite-rich units are in water-lain and ash-fall tuff. The Late Devonian and Early Carboniferous Drummond basin to the north has a similar stratigraphy, and the zeolite occurs in similar units. Such units contain up to 60 weight percent zeolite, which is in both basins a heulandite group mineral. Because of the fine-grained nature of the zeolite crystals, microprobe analyses have large charge-balance errors, but show that it is either heulandite-Ca or clinoptilolite-Ca. It is, nonetheless, remarkable that the zeolite has remained unchanged since diagenesis.

Other important deposits of zeolitized ignimbrite sheets occur in southwestern Cuba and south Mexico (Popov et al. 2006).

Deep marine sediment.  Phillipsite and analcime were discovered by Murray and Renard (1891) in deep-sea sediment collected by the Challenger Expedition. Following several discoveries in the 1960's, a great many more occurrences were found in the core from holes drilled by the Deep Sea Drilling Project. Clinoptilolite-K with phillipsite-K and only a few other zeolites (analcime, harmotome, erionite, and laumontite) are among the authigenic silicate minerals in many different kinds of deep-sea sediment. In general sediments to which the name deep-sea is applied are very fine-grained, occurring in ocean basins well distant from continents and having accumulated at very low rates, 5 m per 106 years.

A great proportion of the clinoptilolite occurrences are in pelagic clay and siliceous microfossil ooze, and chalk. Much less occurs in volcaniclastic sediment. In general, these sediments are very fine-grained, consisting of various clay minerals, calcite, and poorly crystallized silica minerals, such as opal-CT. Clinoptilolite crystals are euhedral and 2 to 40 µm in length, and comprise 10 to 20% of the sediment. Clinoptilolite has been found in core from all parts of all ocean basins (see Boles, 1977, Iijima 1978, and Kastner and Stonecipher 1978). In general, phillipsite occurs in the shallowest levels from very near the water-sediment interface to several hundred meters depth, and clinoptilolite occurs in the deeper and older sections. The zeolite occurrences in deep-sea sediment recovered from legs 1 through about 40 have been reviewed by Stonecipher (1976), Iijima (1978), Boles (1977), and Kastner and Stonecipher (1978).

Even though crystals of clinoptilolite separated from deep-sea sediment are euhedral and clean, their small size (5 to 15 μm) makes obtaining high quality analyses difficult with the electron probe microanalyzer. Good data have been published by Stonecipher (1978) and Boles and Wise (1978). Almost all analyzed samples are clinoptilolite-K, but a few are clinoptilolite-Ca and clinoptilolite-Na still with abundant K, showing that this zeolite has preferentially fractionated K from the interstitial water. Abundant calcite with the nanofossil chalks may account for those few samples with dominant Ca.

There is no compelling textural evidence demonstrating a precursor phase for deep-sea clinoptilolite, such as volcanic glass. A few examples have been found of clinoptilolite replacing siliceous radiolarian tests (Fan and Zemmels 1972). Boles and Wise (1978) show that the conversion of phillipsite to clinoptilolite requires only the addition of water and silica. Therefore, they suggest that phillipsite forms initially in deep-sea sediment as a silica-deficient, metastable phase. With time it dissolves in the pore fluids, and the more stable phase, clinoptilolite, crystallizes where sufficient silica is available.

Diagenesis of mafic lava flows.
The clinoptilolite series minerals are much less common than heulandite in basaltic rocks, but significant occurrences are known. Clinoptilolite-K (the type clinoptilolite) occurs as colorless crystals in altered amygdaloidal basalt breccia exposed on a ridge trending northeast of Hoodoo Peak, Park County Wyoming, USA. (Pirsson 1890). Clinoptilolite-Na forms blocky, crystals in fractures in deeply weathered porphyritic olivine basalt flow-breccia along the north shore of Kamloops Lake, British Columbia, Canada, and in fractures of basalt near Agoura, Santa Monica Mountains, Los Angeles County, California, USA. (Wise et al. 1969). At both localities it is associated with ferrierite and chalcedony. Clinoptilolite-Ca is also known from a few rare occurrences in basalt, such as Kuruma Pass, Fukushima Prefecture, Japan (Koyama and Takeuchi 1977) and in the brecciated tholeiitic basalt of the Columbia River Group, near Altoona, western Wahkiakum County, Washington, USA., where it forms color, blocky crystals in small vesicles and breccia cavities and is associated with mordenite, dachiardite-Na, ferrierite-Na, siderite, and smectite (Wise and Tschernich 1976). Most of these occurrences are in slightly altered host rocks, showing no evidence of pervasive hydrothermal alteration.

Hydrothermal alteration
Active or recently geothermal systems. Replacement of rhyolite tuff intercalated with siltstone and diatomite in lake sediment of the Taupo Volcanic Zone, New Zealand, has produced significant deposits of mordenite and clinoptilolite (Brathwaite 2003; Brathwaite and Rae 2021). The zeolite deposits are associated with sinter, hydrothermal eruption breccias and silicified fault breccias that represent surface or near-surface geothermal activity. Mordenite and clinoptilolite occur in the lower temperature (60-110°C) parts of some active or recently active geothermal systems elsewhere in the Taupo Volcanic Zone. (Steiner 1953, 1977; Krupp and Seward 1987; Henneberger and Browne 1988; Hedenquist and Browne 1989; Chambefort et al. 2017). At Ohakuri dam in the Taupo Volcanic Zone, a recently active geothermal system, hydrothermal alteration zones consist of an innermost quartz-adularia-illite±chlorite zone, which grades into a peripheral zone of mordenite + clinoptilolite + adularia + opal + smectite alteration (Henneberger and Browne 1988;, Brathwaite and Rae 2021). At the Hishikari (Japan) Pleistocene epithermal Au-Ag deposit, zeolites occur in cristobalite-smectite (clinoptilolite), quartz-smectite (mordenite), and interlayered clay (laumontite) alteration zones, which envelope a central chlorite-sericite zone (Izawa et al. 1990). Mordenite occurs in a zeolite (mordenite-clinoptilolite-smectite-opal-CT) alteration zone at Muka, Japan (Maeda 1998). Drillhole temperatures in geothermal systems indicate that mordenite ± clinoptilolite alteration coincides with neutral to alkaline pH, dilute chloride liquid in the temperature range of 60–110°C at Wairakei and Ohaaki (Steiner 1977; Browne 1978), 40–200°C at Yellowstone, USA (Bargar and Keith 1995), and <20–160°C at Sanzugawa, Japan (Utada et al. 1999, Utada 2001b). In the Sanzugawa caldera, geothermal alteration assemblages of clinoptilolite + mordenite + smectite + opal replace volcanic glass in tuffs and pumice tuffs. Samples of fluids in geothermal drill holes at Sanzugawa are characterized by alkaline pH (7.7 to 10.0) and dilute NaCl liquids of meteoric origin. Utada et al. (1999) recognized clinoptilotite- and mordenite-predominant subzones formed at temperatures of <80°C and <180°C, respectively. The clinoptilolite-mordenite alteration was termed “caldera-type zeolitization” by Utada et al. (1999). Mordenite-clinoptilolite-smectite-opal-CT alteration in Quaternary rhyolitic pyroclastics has also been described from the Greek island of Polyegos (Kitsopoulos 1997).

A similar “caldera-type” alteration assemblage of smectite + clinoptilolite + mordenite + cristobalite + opal-CT replaces groundmass and fills voids in rhyolitic tuffs and lake sediments in the Quaternary Valles caldera, New Mexico (Chipera et al. 2008). Mordenite is common as glass shard replacement. Thermodynamic modeling of zeolite stability in Valles caldera field, under amorphous-silica saturated (i.e., presence of opal-CT) conditions at 25°C and 99°C, indicate that mordenite and clinoptilolite have large stability fields, with mordenite being favored by more sodic solutions and slightly higher temperatures (Chipera et al., 2008). These authors noted that a volcanic glass precursor is required to achieve the supersaturation of amorphous silica in the fluids for zeolite formation, and they suggested that zeolite formation was promoted by saturation with a mixture of meteoric waters and degassed hydrothermal liquids. The dissolution of the glass to form zeolites is accompanied by release of silica into solution that results in amorphous silica saturation with precipitation of opal (e.g. Cerri et al. 2001), and an increase in the pH of the fluid (e.g. Hall 1998; Sheppard and Hay 2001). The reaction of volcanic glass with water promotes a rise in pH, because dissolution involves a cation exchange at the glass surface, whereby H3O+ or H2+ enters the glass from solution while Na+, and K+ and Ca+ enter the solution from the glass. The key requirement for zeolite formation is an increase in the activity of (Na+ + K+ + Ca+)/H+, with a consequent increase in the pH of the solution (Sheppard and Hay 2001). The occurrence of mordenite + clinoptilolite + opal-A + opal-CT ± smectite in the Ngakuru area of the Taupo Volcanic Zone is similar to the low-temperature (60–150°C) “caldera-type zeolitization” of Utada et al. (1999), Utada (2001) and Chipera et al. (2008) that occurs at shallow depths in rhyolitic caldera settings. At Mangatete, the dominance of clinoptilolite in the upper part of sequence, with mixed clinoptilolite-mordenite assemblages in the middle and lower part of the sequence suggests a temperature zonation, similar to that at Sanzugawa and also Ohakuri Dam (Brathwaite and Rae 2021).

The occurrence of clinoptilolite as fine-grained crystals in massive beds allows it to be mined and used in applications where large amounts of material are required. Significant deposits of clinoptilolite occur in several countries, especially in Bulgaria, Hungary, Cuba, Mexico, Russia, Italy, Jordan, and the United States.

Many applications exploit the ion exchange properties, which are attractive for agronomy, horticulture and soil remediation where the zeolite can be added to chemical fertilizers to improve the soil chemical and physical properties for plant growth, to increase fertilizer efficiency and to reduce the leaching of nutrients. Treatment of effluents containing radioactive contaminants or other heavy metals. Other applications make use of the molecular sieve properties, to trap or separate gases in agriculture (e.g. ammonia).

Surfactant (surface active agent) modification of clinoptilolite enhances its use as a sorbent for various solutes not or little affected by the untreated zeolite (Bowman 2003). Some examples are CrO₄^2-, organic molecules (e.g. benzene), and certain biological pathogens.

Akizuki, M., Kudoh, Y., Nakamura, S. (1999) Growth texture and symmetry of heulandite-Ca from Poona, India. Can. Mineral. 37, 1307-1312.

Alberti, A. (1972) On the crystal structure of the zeolite heulandite. Tschermaks Mineral. Petrogr. Mitt. 18, 29-146.

Alberti, A. (1975) The crystal structure of two clinoptilolites. Tschermaks Mineral. Petrogr. Mitt. 22, 25-37.

Alberti, A. and Vezzalini, G. (1983) The thermal behavior of heulandites: A structural study of the dehydration of the Nadap heulandite. Tschermaks Mineral. Petrogr. Mitt. 31, 259-270.

Aleksiev, B and Djourova, E.G. (1975) On the origin of zeolitic rocks. C. R. Acad. Bulg. Sci. 28, 517-520.

Armbruster, T. (1993) Dehydration mechanism of clinoptilolite and heulandite: Single-crystal X-ray study of Na-poor, Ca-, K-, Mg-rich clinoptilolite at 100 K. Am. Mineral. 78, 260-264.

Armbruster, T. and Gunter, M.E. (1991) Stepwise dehydration of heulandite-clinoptilolite from Succor Creek, Oregon, U.S.A.: A single crystal X-ray study at 100 K. Am. Mineral. 76, 1872-1883.

Bargar, K.E. and Keith, T.E.C. (1995) Calcium zeolites in rhyolitic drill cores from Yellowstone National Park, Wyoming, in Ming, D.W., and Mumpton, F.A. eds., Natural Zeolites. International Commission on Natural Zeolites, Brockport, New York, p. 69-86.

Bellanca, A., Di Caccamo, A. and Neri, R. (1980) Mineralogia e geochemicia di alcuni suoli della Sicilia Centro-Occidentale: Studio delle variazoni composizionali lungo profili pedologici in relazione ai litotipi d'orgine. Mineral. Petrogr. Acta 24, 1-15.

Bish, D.L. (1988) Effects of composition on the dehydration behavior of clinoptilolite and heulandite. In Occurrence, Properties and Utilization of Natural Zeolites. D. Kallo and H.S. Sherry (eds). Akademiai Kiado, Budapest, 565-576.

Bish, D.L. and Boak, J.M. (2001) Cinoptilolite-heulandite nomenclature. Natural Zeolites: occurrence, properties, applications. Miner. Soc. Am., Reviews Mineral. and Geochem., 45, 207-216.

Bish, D.L. and Ming, D.W., Editors (2001) Natural Zeolites: occurrence, properties, applications. Miner. Soc. Am., Reviews Mineral. and Geochem., 45, 654 pp.

Brito-Rojas, A.D.; Coutin-Correa, D.P., and Rodriguez-Fuentes, G. (2017) Sedimentary Zeolite Deposits in Cuba. International Zeolite Association, Commission on Natural Zeolites, Catalog of Deposits: Cuba. http://www.iza-online.org/natural/default.htm

Boles, J. R. (1977) Zeolites in deep-sea sediments. in Mineralogy and Geology of Natural Zeolites, Miner. Soc. Amer., Short Course Notes, 4, 137-163.

Boles, J.R. and Wise, W.S. (1978) Nature and origin of deep-sea clinoptilolite. In Sand, L.B. and Mumpton, F.A. (eds). Natural Zeolites: Occurrence, Properties, Use, Pergamon Press, Elmsford, New York, 235-244.

Bowman, R.S. (2003) Applications of surfactant-modified zeolites to environmental remediation. Microporous Mesoporous Mater. 61, 43-56.

Brathwaite, R.L. (2003) Geological and mineralogical characterization of zeolites in lacustrine tuffs, Ngakuru, Taupo Volcanic Zone, New Zealand. Clays Clay Minerals, 51, 589-598.

Brathwaite R.L. and Rae A. (2021) Epithermal zeolite alteration associated with siliceous sinters, hydrothermal eruption breccias and gold-silver mineralization, central Taupo Volcanic Zone, New Zealand. Econ. Geol. 116, 1093-1114.

Bresciani-Pahor, N., Calligaris, M., Nardin, G., Randaccio, L., Russo, E., and Comon-Chiaromonti, R. (1980) Crystal structure of a natural and partially Ag-exchanged heulandite. J. Chem. Soc., Dalton Trans. 1980, 1511-1514.

Brown, G., Catt, J.A. and Weir, A.H. (1969) Zeolites of the clinoptilolite-heulandite type in sediments of south-east England. Min. Mag. 37, 480-488.

Browne, P.R.L. (1978) Hydrothermal alteration in active geothermal fields. Ann. Reviews Earth Planetary Science, 6, 229–250.

Broxton, D.E., Bish, D.L., and Warren, R.G. (1987) Distribution and chemistry of diagenetic minerals at Yucca Mountain, Nye County, Nevada. Clays Clay Minerals 35, 89-110.

Cappelletti, P., Langella, A., and Cruciani, G. (1999) Crystal-chemistry and synchrotron Rietveld refinement of two different clinoptilolite from volcaniclastics of North-Western Sardinia. Eur. J. Mineral. 11, 1051-1060.

Chambefort, I., Lewis, B., Simpson, M.P., Bignall, G., Rae, A.J., and Ganefianto, N. (2017) Ngatamariki geothermal system: magmatic to epithermal transition in the Taupo Volcanic Zone, New Zealand. Econ. Geol. 112, 319–346.

Cerri, G., Cappelletti. P., Langella, A. and de’Gennaro, M. (2001) Zeolitization of Oligo-Miocene volcaniclastic rocks from Logudoro (northern Sardinia, Italy). Contrib. Mineral. Petrol. 140, 404–421.

Chambefort, I., Lewis, B., Simpson, M.P., Bignall, G., Rae, A.J., and Ganefianto, N. (2017) Ngatamariki geothermal system: magmatic to epithermal transition in the Taupo Volcanic Zone, New Zealand. Econ. Geol. 112, 319–346.

Chipera, S.J. and Apps, J.A. (2001) Geochemical stability of natural zeolites. In: Bish, D.L., and Ming, D.W., eds. Natural zeolites: occurrence, properties, applications: Mineralogical Society of America: Reviews Mineral. Geochem. 45, 117–161.

Chipera, S.J., Goff, F., Goff, C.J. and Fittipaldo, M. (2008) Zeolitization of intracaldera sediments and rhyolitic rocks in the 1.25 Ma lake of Valles caldera, New Mexico, USA. J. Volcan. Geotherm. Res. 178, 317–330.

Cocheme, J.J., Lassauvagerie, A.C., Gonzalez-Sandoval, J., Perez-Segura, E. and Munch, P. (1996) Characterization and potential economic interest of authigenic zeolites in continental sediments from NW Mexico. Mineral Deposita 31, 482-491.

Coombs, D.S., Alberti, A., Armbruster, T., Artioli, G., Colella, C., Galli, E., Grice, J.D., Liebau, F., Mandarino, J.A., Minato, H., Nickel, E.H., Passaglia, E., Peacor, D.R., Quartieri, S., Rinaldi, R., Ross, M., Sheppard, R.A., Tillmanns, E., and Vezzalini, G. (1997) Recommended nomenclature for zeolite minerals: Report of the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names. Can. Mineral., 35, 1571-1606.

Coombs, D.S. (1954) The nature and alteration of some Triassic sediments from Southland, New Zealand. Trans. Roy. Soc. New Zealand 82, 65-109.

Cross, W. and Eakins, L.G. (1886) On ptilolite, a new mineral. Am. J. Sci. 132, 117-121.

De Pablo-Galan, L., Chavez-Garcia, M., and Cruz-Sanchez, M. (1996) Sedimentary zeolites in the Sierra Madre Del Sur and Sierra Madre Occidental, Mexico. Revista Mexicanna de Ciencias Geologicas 13, 188-200.

Deer, A., Howie, R., Wise, W.S., and Zussman, J. (2004). Rock Forming Minerals. vol. 4B. Framework Silicates: Silica Minerals, Feldspathoids and the Zeolites. The Geological Society, London.

Flood, P.G. (1995) Australian occurrences of Ca-type clinoptilolite. In Ming, D.W. and Mumpton, F.A. (eds). Natural Zeolites '93, Int. Comm. Natural Zeolites, Brockport, New York, 15-21.

Flood, P.G. and Taylor, J.C. (1991) Mineralogy and geochemistry of Late Carboniferous zeolitites, near Werris Creek, New South Wales, Australia. Neues Jahrb. Miner. Mh. 1991, 49-62.

Gonzalez,E.M., Reyes,L.A., Cruz, F. Pupo, R., and Mendez, D. (1991) Caracteristicas de las tobas intemperizadas en la region occidental de Cuba. In Funetes, G.R. and Gonzalez, A.G. (Eds). Memoirs of the 3rd International Conference on the Occurrence, Properties and Utilization of Natural Zeolites, Havana, Cuba, 49-52.

Gottardi, G. and Obradovic, J. (1978) Sedimentary zeolites in Europe. Fortschr. Miner. 56, 316-366.

Gude, A.J., 3rd. and Sheppard, R.A. (1988) A zeolitic tuff in a lacustrine facies of the Gila Conglomerate near Buckhorn, Grant County, New Mexico. U.S. Geol. Surv., Bull. 1763, 22sp.

Gundogdu, M.N., Yalcin, H., Temel, A. and Clauer, N. (1996) Geological, mineralogical and geochemical characteristics of zeolite deposits associated with borates in the Bigadic, Emet and Kirka Neogene lacustrine basins, western Turkey. Mineral Deposita 31, 492-513.

Gunter, M.E., Armbruster, T., Kohler, T., and Knowles, C.R. (1994) Crystal structure and topical properties of Na- and Pb-exchanged heulandite-group zeolites. Am. Mineral. 79, 675-682.

Hall, A. (1998) Zeolitisation of volcaniclastic sediments: the role of temperature and pH. J. Sediment. Res. 68, 739–745.

Hambley, T.W., and Taylor, J.C. (1984) Neutron diffraction studies on natural heulandite and partially dehydrated heulandite. J. Solid State Chem. 54, 1-9.

Hay, R.L. (1963) Stratigraphy and zeolitic diagenesis of the John Day Formation of Oregon. Univ. Calif. Pub. in Geol. Sci., 42, no. 5, 199-262.

Hay, R.L. (1966) Zeolites and zeolitic reactions in sedimentary rocks. Geol. Soc. Amer., Special Pap. 85, 130 pp.

Hay, R.L., Shephard, R.A. (2001) Occurrence of zeolites in sedimentary rocks: an overview. In: Bish, D.L. and Ming, D.W. (eds) Natural Zeolites: Occurrence, Properties, Applications. Miner. Soc. Am., Reviews in Mineral. and Geochem., 45, 217-232.

Hedenquist, J.F. and Browne, P.R.L. (1989) The evolution of the Waiotapu geothermal system, New Zealand, based on the chemical and isotopic composition of its fluids, minerals and rocks. Geochem. et Cosmochim. Acta 53, 2235–2257.

Henneberger, R.C. and Browne P.R. (1988) Hydrothermal alteration and evolution of the Ohakuri hydrothermal system. J. Volcano. Geotherm. Res. 34, 211–231.

Hey, M.H. and Bannister, F.A. (1934) Studies on the zeolites. Part VII. "Clinoptilolite", a silica-rich variety of heulandite. Min. Mag. 23, 556-559.

Iijima, A. (1978) Geologic occurrences of zeolite in marine environments. In Sand, L.B. and Mumpton, F.A. (eds). Natural Zeolites: Occurrence, Properties, Use, Pergamon Press, Elmsford, New York, 175-198.

Izawa, E., Urashima, Y., Ibaraki, K., Suzuki, R., Yokohama, T., Kawasaki, K., Koga, A. and Taguchi, S. (1990) The Hishikari gold deposit: high-grade epithermal veins in Quaternary volcanics of southern Kyushu, Japan. J. Geochem. Explor. 36, 1–56.

Jacob, J.S. and Allen, B.L. (1990) Persistence of a zeolite in tuffaceous soils of the Texas Trans-Pecos. Soil Sci. Soc. Amer. J. 54, 549-554.

Kastner, M. and Stonecipher, S.A. (1978) Zeolites in pelagic sediments of the Atlantic, Pacific, and Indian Oceans. In Sand, L.B. and Mumpton, F.A. (eds). Natural Zeolites: Occurrence, Properties, Use, Pergamon Press, Elmsford, New York, 199-220.

Kitsopoulos, K.P. (1997) The genesis of a mordenite deposit by hydrothermal alteration of pyroclastics on Polyegos Island, Greece. Clays Clay Min. 45, 632–648.

Koyama, K. and Takeuchi, Y. (1977) Clinoptilolite: the distribution of potassium atoms and its role in thermal stability. Z. Kristallogr. 145, 216-239.

Krupp, R.E. and Seward, T.M. (1987) The Rotokawa geothermal system, New Zealand: an active epithermal gold-depositing environment. Econ. Geol. 82, 1109–1129.

Lander, R.H. and Hay, R.L. (1993) Hydrogeologic control on zeolitic diagenesis of the White River sequence. Geol. Soc. Amer., Bull. 105, 361-376.

Langella, A., Cappelletti, P., de Gennaro, M. (2001) Zeolites in closed Hydrologic systems. In: Bish, D.L. and Ming, D.W. (eds) Natural Zeolites: Occurrence, Properties, Applications. Miner. Soc. Am., Reviews in Mineral. & Geochem., 45, 235-260.

Levy, S.S. and O'Neil, J.R. (1989) Moderate-temperature zeolitic alteration in a cooling pyroclastic deposit. Chem. Geol. 76, 321-326.

Maeda, H. (1998) Relationships between volcanism, hydrothermal alteration and epithermal gold-silver mineralization in the Muka mine area in the Kitami metallogenic province, Hokkaido, Japan. Resource Geol. 48, 97–208.

Mason, B. and Sand, L.B. (1960) Clinoptilolite from Patagonia; the relationship between clinoptilolite and heulandite. Am. Mineral. 45, 341-350.

Merkle, A.B. and Slaughter, M. (1968) Determination and refinement of the structure of heulandite. Am. Mineral. 53, 1120-1138.

Ming, D.W. and Boettinger, J.L. (2001) Zeolites in Soil Environments. In Bish, D.L. and Ming, D.W. (eds) Natural Zeolites: Occurrence, Properties, Applications, Miner. Soc. Am. Reviews in Mineral. & Geochem., 45, 323-346.

Ming, D.W. and Dixon, J.B. (1986) Clinoptilolite in south Texas soils. Soil Sic. Soc. Amer. J. 50, 1618-1622.

Mumpton, F.A. (1960) Clinoptilolite redefined. Am. Mineral. 45, 351-369.

Munch, P., Duplay, J. Cocheme, J.J. (1996) Alteration of acid vitric tuffs interbedded in the Bacaurit Formation, Sonora, State, Mexico. Contribution of transmission and analytical electron microscopy. Clays Clay Minerals 44, 49-67.

Murray, J. and Renard, A.F. (1891) Report on Scientific Results of the Voyage of "H.M.S. Challenger" during the years 1873-1876; Deep Sea Deposits. Johnson Reprint Co., London, 525 pp.

Nornberg, P. (1990) A potassium-rich zeolite in soil development on Danian chalk. Min. Mag. 54, 91-94.

Obradovic, J. (1979) Authigenic minerals in middle Triassic volcanoclastic rocks in Dinarides. Bull. Mus. Hist. Nat. Belgrade, Ser. A 34, 13-36.

Obradovic, J. (1988) Occurrences and genesis of sedimentary zeolites in Serbia. In Kallo, D. and Sherry, H.S. (eds). Occurrence, Properties and Utilization of Natural Zeolites. Akademiai Kiado, Budapest, 59-70.

Ogihara, S. and Iijima, A. (1990) Exceptionally K-rich clinoptilolite-heulandite group zeolites from three offshore boreholes off northern Japan. Eur. J. Mineral. 2, 819-826.

Petrova, V.V., Badamgarev, D., Sokolova, A.L., and Serebrennikova, N.D. (1987) A new type of zeolite of volcanic-limnic origin (Southern Gonolia). Lith. and Miner. Res. 22, 373-391.

Pirsson, L.V. (1890) On mordenite. Am. J. Sci. 140, 232-237.

Popov, N., Yanev, Y., Iliev, Tz., and Popova, T. (2006) Clinoptilolitized pyroclastic rocks from Oaxaca (south Mexico): A mineralogical and technological study. In Bowman, R.S. and Delap, S.E. (Eds.) Zeolite '06 - 7th Int. Conf. on the Occurrence, Properties, and Utilization of Natural Zeolites, Socorro, New Mexico USA 16-21, 2006, Abstract, 208-209.

Sani, A., Vezzalini, G., Ciambelli, P., and Rapacciuolo, M.T. (1999) Crystal structure of hydrated and partially NH4-exchanged heulandite. Microporous Mesoporous Materials 31, 263-270.

Schaller, W.T. (1923) Ptilolite and related zeolites. In, Proc. Societies (E.T. Wherry, ed.) Am. Mineral. 8, 93-94.

Schaller, W.T. (1932) The mordenite - pitlolite group: clinoptilolite, a new species. Am. Mineral. 17, 128-134.

Seryotkin, Y.V. (2016) High-pressure behavior of HEU-type zeolites: X-ray diffraction study of clinoptilolite-Na, Microporous Mesoporous Mater., 235, 20-31.

Sheppard, R.A. (1991) Zeolitic diagenesis of tuffs in the Miocene Chalk Hills Formation, western Snake River Plain, Idaho. U.S. Geol. Surv., Bull.  1963, 19 pp.

Sheppard, R.A. (1994) Zeolitic diagenesis of tuffs in the Miocene lacustrine rocks near Harney Lake, Harney, County, Oregon . U.S. Geol. Surv., Bull.  2108, 28 pp.

Sheppard, R.A. and Gude, A.J. 3rd. (1968) Distribution and genesis of authigenic silicate minerals in tuffs of Pleistocene Lake Tecopa, Inyo County, California. U.S. Geol. Surv., Prof. Paper  597, 38 pp.

Sheppard, R.A. and Gude, A.J. 3rd. (1969) Diagenesis of tuffs in the Barstow Formation, Mud Hills San Bernardino County, California. U.S. Geol. Surv., Prof. Paper  634, 35 pp.

Sheppard, R.A. and Gude, A.J. 3rd. (1973) Zeolites and associated authigenic silicate minerals in tuffaceous rocks of the Big Sandy formation, Mohave County, Arizona. U.S. Geol. Surv., Prof. Paper  830, 36 pp.

Sheppard, R.A., Gude, A.J. 3rd, and Edson, G.M. (1978) Bowie zeolite deposit, Cochise and Graham Counties, Arizona. In, Sand, L.B. and Mumpton, F.A. (eds). Natural Zeolites: Occurrence, Properties, Use, Pergamon Press, Elmsford, New York, 319-328s.

Sheppard, R.A. and Hay, R.L. (2001) Formation of zeolites in open hydrologic system. In: Bish, D.L. and Ming, D.W. (eds) Natural zeolites: occurrence, properties, applications. Miner. Soc. Am., Reviews Mineral. & Geochem. 45, 261–276.

Smyth, J.R., Spaid, A.T., and Bish, D.L. (1990) Crystal structures of a natural and a Cs-exchanged clinoptilolite. Am. Mineral. 75, 522-528.

Steiner, A. (1953) Hydrothermal rock alteration at Wairakei, New Zealand. Econ. Geol. 48, 1–13.

Steiner, A. (1977) The Wairakei geothermal area North Island, New Zealand. New Zealand Geological Survey Bulletin 90. Department of Scientific and Industrial Research, Wellington, 136 pp.

Stolz, J., Yang, P., and Armbruster, T. (2000a) Cd-exchanged heulandite: Symmetry lowering and site preference. Microporous Mesoporous Mater. 37, 233-242.

Stolz, J., Armbruster, T., and Hennessey B. (2000b) Site preference of exchanged alkylammonium ions in heulandite: Single crystal X-ray structure refinements. Z. Kristallogr. 215, 278-287.

Stonecipher, S.A. (1976) Distribution of deep-sea phillipsite and clinoptilolite. Chem. Geol. 17, 307-318.

Stonecipher, S.A. (1978) Chemistry of deep-sea phillipsite, clinoptilolite, and host sediments. In Sand, L.B. and Mumpton, F.A. (eds). Natural Zeolites: Occurrence, Properties, Use, Pergamon Press, Elmsford, New York, 221-234.

Strzelecki, A.C., Chariton, S., Cockreham, C.B. Michael T. Pettes, M.P., Prakapenka, V., Chidester, B.A., Wu, D., Bradley, C.R., Euler, G.G., Guo, X., Boukhalfa, H. and Xu, H. (2022) Determination of P–V equation of state of a natural clinoptilolite using high-pressure powder synchrotron X-ray diffraction. Phys. Chem. Minerals 49, 45.

Sugiyama, K. and Takeuchi, Y. (1986) Distribution of cations and water molecules in the heulandite-type framework. Stud. Surf. Sci. Catal. 28, 449-456.

Turner, C.E. and Fishman, N.S. (1991) Jurassic Lake T'oo'dichi': a large alkaline, saline lake, Morrison Formation, eastern Colorado Plateau. Geol. Soc. Amer., Bull. 103, 538-558

Utada, M. (2001a) Zeolites in burial diagenesis and low-grade metamorphic rocks. In: Bish, D.L. and Ming, D.W. (eds) Natural Zeolites: Occurrence, Properties, Applications. Miner. Soc. Am., Reviews in Mineral. & Geochem., 45, 277-304.

Utada, M. (2001b) Zeolites in hydrothermally altered rocks. In: Bish, D.L. and Ming, D.W. (eds) Natural Zeolites: Occurrence, Properties, Applications. Miner. Soc. Am., Reviews in Mineral. & Geochem., 45, 305–322.

Utada, M., Shimizu, M., Ito, T. and Inoue, A. (1999) Alteration of caldera-forming rocks related to the Sanzugawa volcanotectonic depression, northeast Honshu, Japan – with special reference to “Caldera-type zeolitization”. Resource Geol. Special Issue 20, 129–140.

Whateley, M.K.G., Querol, X., Fernandez-Turiel, J.L., and Tuncali, E. (1996) Zeolites in Tertiary coal from the Cayirhan mine, Beypazari, Turkey. Mineral Deposita 31, 529-538.

Wise, W.S., Nokleberg, W.J., and Kokinos, M. (1969) Clinoptilolite and ferrierite from Agoura, California. Am. Mineral. 54, 887-895.

Wise, W.S. and Tschernich, R.W. (1976) Chemical composition of ferrierite. Am. Mineral. 61, 60-66.

Vanev, Y., Cochema, J.-J., Ivanova, R., Grauby, O., Burlet, E., Pravchanska, R., (2006) Zeolites and zeolitization of acid pyroclastic rocks from paroxysmal Paleogene volcanism, Eastern Rhodopes, Bulgaria. Neues. Jahrb. Miner. Abh.,182/3, p. 265-283.

Yang, P. and Armbruster, T. (1996) Na, K, Rb, and Cs exchange in heulandite single crystals: X-ray structure refinements at 100 K. J. Solid State Chem. 123, 140-149.

Updated: April 2025.