Heulandite-Na

Heulandite was first described by Brooke (1822), separating distinctly monoclinic crystals from what had been called Blätter-Zeolith, which included stilbite and other platy minerals. No specific occurrence was chosen as a type locality. The name honors John Henry Heuland (1778-1856), an English mineral collector. Coombs et al. (1997) elevated the name to series status to include four species. Heulandite-Ca is the new name for the original material, in which Ca is the most abundant non-framework cation. The designated type example is from the Faeroe Islands (Alberti 1972). Heulandite-Na is a separate species with the type example from Challis, Idaho, USA (Boles 1972), and includes alkali-rich heulandite that in some instances had been called clinoptilolite. Heulandite-K is a separate species with the type example from Albero Bassi, Veneto, Italy (Passaglia 1969), and heulandite-Sr is based on a single occurrence at the Campegli mine, Genova, Liguria, Italy (Lucchetti et al. 1982). A fifth species, heulandite-Ba, from Kongsberg, Norway (Larsen et al. 2005) has been added to this series.
In their review of zeolite nomenclature Coombs et al. (1997) chose to retain both the heulandite and clinptilolite names for mineral series, even though all members have the same framework structure. Although the term clinoptilolite was initially tied to thermal behavior, Coombs et al. (1997) defined an Si/Al compositional boundary between the two series. The heulandite series pertains to all those samples with Si/Al less than 4 (TSi < 0.80 or  < 28.8 Si per pfu), and the clinoptilolite series to include all compositions with Si/Al greater than 4. This artificial boundary between the two series of minerals (see the compositional diagram below) suggests that sharp distinctions in various properties, chemical and physical, may not be present. In fact gradations across the compositional field are to be expected. For a discussion of this nomenclature problem and some guidance in distinguishing between heulandite and clinoptilolite, see Bish and Boak (2001).
In the absence of compositional data, use of the term heulandite without any suffices is appropriate.

Both heulandite and clinoptilolite 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 heulandite and clinoptilolite are commonly described to be monoclinic, space group C2/m (e.g. Alberti 1975, Koyama and Takéuchi 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 Salughter 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) (see figure). 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).

The crystal structure of heulandite-Ca (Faroe Islands, Denmark) with Ca and H₂O molecule sites from the refinement of Alberti (1972).

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 heulandite and clinoptilolite. 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 growing 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 clintoptilolite. 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 Takéuchi 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 with 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 Takéuchi 1977, Sugiyama and Takéuchi 1986, Armbruster 1993).
Heulandite and clinoptilolite 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, occurring in the A channel are generally only partially occupied (Koyama and Takéuchi 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).

Plotted here are heulandite compositions that represent the major types of occurrence, cavities in volcanic rocks, diagenetic replacement of volcaniclastic sediment and sedimentary rock, and hydrothermal veins in gneissic to pegmatitic rock. The most familiar and common species of the series is heulandite-Ca, which occurs mostly in cavities of basaltic lava flows. However, some occurrences are known in thick accumulations of andesitic to rhyolitic volcaniclastic rocks. This species has low Si content, about 27 per unit cell, and high water, 23 to 25 H₂O per cell. Alkali-dominant heulandite (heulandite-Na and heulandite-K), which has the highest Si, limited at T_Si = 0.80 or Si/Al = 4.0 by the definition of the species, occurs in siliceous and alkali-enriched environments. These species are much less common with only two known examples of heulandite-K. Several of these samples were previously classified as clinoptilolite, using the Mason and Sand (1968) definition for the species, based on high alkali content.

R²R²⁺ - R⁺ - Si compositional plot (above) and Na - Ca - K plot (below) of the heulandite series analyses (red squares) compiled in Deer et al. (2004). Black circles represent clinoptilolite analyses, all with Si/Al greater than 4.0.

Although it is common for most heulandite to contain minor amounts of Sr and Ba, only one locality, Campegli mine, Liguria, Italy, has produced crystals with zones, containing Sr in dominant proportions, and Ba dominant heulandite occurs only Kongsberg, Norway (Larsen et al. 2005). Mg is a fairly common constituent in heulandite, ranging up to 0.65 atoms pfu. Fe does occur in tetrahedral sites, but apparent amounts over 0.5 atoms/cell may be from included hematite, especially in reddish crystals.

Heulandite series minerals are common zeolites, occurring in altered mafic rocks and sediment in thick marginal basins, continental accumulations in thick basin fills, and in island arc settings or flood basalt. Alteration reactions may occur upon burial or accelerated by slightly elevated temperatures near heat sources, such as volcanic conduits.

Diagenesis and burial metamorphism of sediment and sedimentary rocks.
Heulandite series minerals commonly replace glass with moderate amounts of silica available, such as that in basaltic to andesitic volcaniclastic sediment.

Marine sediment from arc-source terrains. The benchmark paper by Coombs (1954) demonstrated the importance of zeolite minerals as products of diagenesis and early stages of metamorphism of thick sections of marine volcanic sedimentary rock. The Southland Syncline in the Taringatura Hills, New Zealand, exposes about 10 km of Triassic sedimentary rock with a large component of volcanic detritus. Heulandite-Ca and analcime occur in the upper two-thirds of this section with laumontite and albite in the lower third. With a lack of intrusive rocks the progressive changes in alteration minerals with depth apparently occur in response to the temperature and pressure increase from burial.

Later work by Boles (1974) and Boles and Coombs (1977) on a similar section of the Southland Syncline exposed in the Hokonui Hills showed that some of the simple concepts tentatively proposed by Coombs (1954) could not account for complexities of mineral occurrence. The overlapping and repeated occurrences of laumontite and heulandite suggested to Boles and Coombs (1977) that many other factors could play a role in various phase appearances, such as ionic activity in stratal waters, P(CO2), incomplete reactions, and the relationship between P(total) and P(fluid). Boles and Coombs (1975) estimate the average geothermal gradient in the Southland syncline to have been about 25°/km, based on the depth where analcime + quartz reacts to form albite, estimated to occur at about 190°C (Liou, 1971). Such low geothermal gradients occur in areas of rapid volcanogenic sediment accumulation with no additional heat sources.

In both the Hokonui and Taringatura Hills sections the heulandite group minerals range in composition from heulandite-Ca to clinoptilolite-Ca (Boles and Coombs 1975). Both minerals occur with chlorite and celadonite as replacements of relict glass shards with no evidence of a precursor mineral. Because there is no correlation between depth and composition, Boles and Coombs (1975) suggest that the composition (Si/Al) is controlled by the composition of the altering glass. Petrographic evidence that laumontite replaces heulandite with depth includes the partial destruction of shard outlines and common association with detrital plagioclase that has been more extensively altered than higher in the section (Boles and Coombs 1975).

Diagenesis of mafic lava flows.
Heulandite series minerals are common in basalt cavities (Tschernich 1992). Heulandite-Ca is by far the most common species and occurs in host rocks that are silica saturated. Some of the classic localities are at Teigarhorn in Berufjord, Iceland; the Faeroe Islands; Nasik and Pune, India; Cape Bomidon, Nova Scotia, Canada; Val di Fassa, Alpe di Siusi, Italy; Paterson, New Jersey, U.S.A. Common associated minerals include analcime, chabazite, stilbite, laumontite, apophyllite, calcite, and quartz. Heulandite-K is known from one locality at Albero Bassi, Vicenza, Italy (Passaglia 1969), where it forms tiny, red crystals in altered basalt. Heulandite-Na is also uncommon, but is presently known from several localities, such as in large cavities in andesite flows south of Challis, Custer County, Idaho, where the red crystals are covered by mordenite, quartz, calcite, and analcime (Ross and Shannon 1924).

To approximate the conditions under which heulandite forms in these localities, it is necessary to use the eastern Iceland occurrences, one of very few regional studies of amygdaloidal zeolites. In eastern Iceland Walker (1960) found regional occurrence of heulandite-Ca in the mesolite-scolecite zone of olivine basalt flows. The boundary with the next lower zone of laumontite cuts across flows, showing that zeolite zones were formed long subsequent to eruption and cooling of the lavas. Observations in geothermal areas of Iceland summarized by Kristmannsdóttir and Tómasson (1978) show that heulandite probably forms at temperatures less than 90°C.

Hydrothermal alteration
Active geothermal systems. In the Iceland geothermal areas heulandite (species unknown, but probably heulandite-Ca) occurs sporadically over the four zones defined by Kristmannsdóttir and Tómasson (1978, p. 284), where the temperature range is between 70° and 110°C. Common associated minerals are thomsonite, stilbite-Ca, epistilbite, and mordenite.

Late stage, deuteric alteration. Two notable occurrences in pegmatite are at Campo, Elba, Italy, where heulandite occurs with dachiardite-Na, mordenite, epistilbite, and stilbite in the core dikes (Gottardi and Galli 1985) and in the Himalaya dike system, San Diego County, California, where heulandite, stilbite, and laumontite are late stage alteration minerals (Foord 1977). This type of occurrence in non-volcanic host rocks suggests the heulandite series minerals grew in warm solutions flowing through the fracture systems.

Hydrothermal settings related to ore deposits. Heulandite-Sr occurs with stilbite, chabazite, calcite, pyrite, and chalcopyrite in fractures in altered ophiolitic rocks in the Campegli Copper Mine, Liguria, Italy (Lucchetti et al. 1982).

Heulandite-Ba occurs as an accessory mineral in hydrothermal veins of the Kongsberg silver deposit type at the Northern Ravnås prospect, southern Vinoren, 14 km NNW of Kongsberg town, Kongsberg ore district, Flesberg community, Buskerud County, Norway. The mineral has also been found at the Bratteskjerpet mine, Saggrenda near Kongsberg, and in hydrothermal veins in quartzite at Sjoa in Sel community, Oppland County, Norway (Larsen et al. 2005).

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.

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.

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., Kohler, T., Meisel, T., Nägler, T. F., Götzinger, M.A. and Stalder, H. A. 1996. The zeolite-fluorite-quartz assemblage of the fissures at Gibelsbach, Fiesch (Valais, Switzerland): crystal chemistry, REE patterns, and genetic speculations. Schweiz. Mineral. Petrogr. Mitt. 76, 131-146.

Bish, D.L. and Boak, J.M. 2001. Cinoptilolite-heulandite nomenclature. In: Reviews in Mineralogy & Geochemistry. 45, Natural Zeolites, (eds.) Bish, D.L. and Ming, D.W., 207-216.

Boles, J.R. 1972. Composition, optical properties, cell dimensions, and thermal stability of some heulandite group zeolites. Am. Mineral. 57, 1463-1493.

Boles, J.R. 1974. Structure, stratigraphy, and petrology of mainly Triassic rocks, Hokonui Hills, Southland, New Zealand. New Zealand J. Geol. Geophys. 17, 337-374.

Boles, J.R. and Coombs, D.S. 1975. Mineral reactions in zeolitic Triassic tuff, Hokonui Hills, New Zealand. Geol. Soc. Amer., Bull. 86, 163-173.

Boles, J.R. and Coombs, D.S. 1977. Zeolite facies alteration of sandstones in the Southland Syncline, New Zealand. Amer. J. Sci., 277, 982-1012.

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.

Brooke, H.J. 1822. On the comptonite of Vesuvius, the brewsterite of Scotland, the stilbite and the heulandite. Edinburgh Phil. J. 6, 112-115.

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

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

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.

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.

Foord, E.E. 1977. The Himalaya dike system, Mesa Grande District, Sand Diego County, California. Min. Rec. 8, 461-474.

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.

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.

Hintze, C. 1897. Handbuch der Mineralogie, vol. 2 (Silikate und Titanate). Von Veit, Leipzig.

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

Kristmannsdóttir, H. and Tómasson, J. 1978. Zeolite zones in geothermal areas in Iceland. In Sand, L.B. and Mumpton, F.A. (eds). Natural Zeolites: Occurrence, Properties, Use, Pergamon Press, Elmsford, New York, 277-284.

Larsen, A.O., Nordrum, F.S., Döbelin, N., Armbruster, T., Petersen, O.V., Erambert, M. 2005. Heulandite-Ba, a new zeolite species from Norway. Eur. J. Mineral. 17, 143-154.

Liou, J.G. 1971. Analcime equilibria. Lithos, 4, 389-402.

Lucchetti, G., Massa, B. and Penco, A.M. (1982) Strontian heulandite from Campegli (eastern Ligurian ophiolites, Italy). Neues Jahrb. Miner., Mh. 1982, 541-550.

Manchester, J.G. 1931. The minerals of New York City and its environs. Bull. New York Min. Club, 3, 1-168.

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.

Passaglia, E. 1969. Le zeoliti di Albero Bassi (Vicenza). Per. Mineral. 38, 237-243.

Ross, C.S. and Shannon, E.V. 1924. Mordenite and associated minerals from near Challis, Custer County, Idaho. Proc. U.S. Nat. Museum  64(19), 1-19.

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.

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.

Stalder, H.A., de Quervain, F., Niggli, E., Graeser, St. and Jenny, V. 1973. Die Mineralfunde der Schweiz, revised edition of Parker, R.L. Die Mineralfunde der Schweizer Alpen, Wepf and Co, Verlag, Basel. 433 pp.

Stolz, J., Yang, P., and Armbruster, T. 2000a. Cd-exchanged heulandite: Symmetry lowering and site preference. Microporous Mesoporous Materials 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.

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

Tschernich, R.W. 1992. Zeolites of the World, Geoscience Press, Phoenix, Arizona. 563 pp.

Walker, G.P.L. 1960. Zeolite zones and dike distribution in relation to the structure of the basalts of eastern Iceland. J. Geol. 68, 515-528.