Phillipsite


Phillipsite Series		Phillipsite-Na \|(Na,K,Ca_0.5)_x(H₂O)₁₂\| [Al_xSi_16-xO₃₂] x = 3.7 – 6.7 Phillipsite-K \|(K,Na,Ca0.5)_x(H₂O)₁₂\| [Al_xSi_16-xO₃₂] x = 3.8 – 6.4 Phillipsite-Ca \|(Ca0.5,Na,K)_x(H₂O)₁₂\| [Al_xSi_16-xO₃₂] x = 4.1 – 6.8

Morphology:
	Equant to prismatic crystals, or in spherical radiating aggregates. Twinning: Cruciform single and double penetration twins {010}, {021}, {110}, ubiquitous.

Physical properties:
	Cleavage: {010}, {100} distinct. Hardness: 4 – 4.5. D = 2.20 gm/cm³. Luster: vitreous. Streak: white.
			Three double-twinned prisms of phillipsite-K, Limberg, Sasbach, Kaiserstuhl, Baden-Württemberg, Germany. Width of image, 3 mm. (© Volker Betz).
Optical properties:
	Color: colorless to yellowish, reddish, colorless in thin section. Biaxial (+). α = 1.483 - 1.504, β = 1.484 - 1.509, γ = 1.486 - 1.514, δ= 0.003 - 0.010, 2Vz = 60° - 80°. Y ˄ a = 46°-65°, X = b, O.A.P. ^ (010).

Crystallography:
	Unit cell data:	Phillipsite-K	a 9.961 – 9.975, b 14.164 – 14.236, c 8.700 – 8.768 Å, β 124.77 – 124.87°. Z = 1, Space group P21/m. (Passaglia et al. 2000)
		Phillipsite-Na	a 10.037 – 10.082, b 14.136 – 14.194, c 8.689 – 8.719 Å, β 125.06 – 125.21°. Z = 1, Space group P21/m (Passaglia et al. 2000)
		Phillipsite-Ca	a 9.874 – 9.995, b 14.208 – 14.271, c 8.690 – 8.735 Å, β 124.64 – 125.09°. Z = 1, Space group P21/m (Passaglia et al. 2000)

Name:
	Phillipsite was described by Lévy (1825) from the type locality Aci Reale, now Acireale, on the slopes of Etna, Sicily, Italy. More recent descriptions of the mineralogy of the Etna area (Di Franco 1942) suggest that the occurrence was probably in nearby basaltic exposures at Aci Castello. The mineral was named after William Phillips (1773-1828), author of geological and mineralogical treatises and a founder of the Geological Society of London. Interestingly Wernekink (1824, 1825) described phillipsite from Annerod (near Giessen, Germany) as calcium-harmotome and then corrected to potassium-harmotome, but did not propose a new name. The phillipsite series was divided into species by the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names (Coombs et al. 1997). The species names are based on the dominant channel cation. The type examples for the new phillipsite species compositions are as follows: phillipsite-Na has the composition from the original phillipsite type locality at Aci Castello, Sicily, Italy; phillipsite-K, Capo di Bove, Rome, Italy; and phillipsite-Ca, Lower Salt Lake Tuff, Puuloa Road near Moanalua Road junction, Oahu, Hawaii (Coombs et al. 1997).

Crystal structure:
	The basic building unit of the phillipsite framework is a chain of doubly connected 4-rings, linking in the UUDD arrangement, generally known as double crankshaft (dcc in PHI). The true space group of the phillipsite series (and isostructural harmotome) is still under debate. Recent X-ray and neutron single-crystal structure refinements between 15 and 293 K confirm the centric space group P21/m for harmotome (Stuckenschmidt et al. 1990) proposed by Rinaldi et al. (1974). There are, however, hints of acentricity (space group P21 or even P1), indicated by piezoelectricity (Sadanga et al. 1961) and optical domains (Akizuki 1985).
	There are three types of channels confined by eight-membered rings of tetrahedra, one parallel to the a-axis (aperture 3.6 Å), shown in the accompanying figure, one parallel to the b-axis (aperture 4.3 x 3.0 Å), and another parallel to the c-axis (aperture 3.3 x 3.2 Å). The double crankshaft chains run parallel to the a-axis (see PHI). Ordering of (Ca,Na) vacancies (C2 site) combined with (Si,Al) order might be responsible for symmetry lowering as discussed above. Stuckenschmidt et al. (1990) proposed a partially ordered (Si,Al) distribution, whereas Rinaldi et al. (1974) stated that the near uniformity of T-O distances gives little or no suggestion of (Si,Al) order.
	Stacking faults on (100) and (010) by a slip of a/2 or b/2 are possible in all frameworks with the double crankshaft chain. Thus, as a result of a/2 faults, diagenetic phillipsite in sedimentary rocks may be composed of phillipsite and merlinoite domains (Gottardi and Galli 1985). Rietveld refinements of K-, NH4-, Ca-, Sr-, and Ba-exchanged phillipsite with three different Si/Al contents were carried out by Passalgia et al. (2000).


Chemical composition:
	The range of compositions of the phillipsite series is graphically illustrated in the accompanying plots. These analyses are from the two major types of phillipsite occurrence, cavities in basaltic rocks and diagenetic replacement of volcaniclastic sediment and sedimentary rocks. The phillipsite series exhibit the widest compositional range of all the zeolite groups. The lowest Si (about 9.2 atoms per unit cell) and highest divalent cation contents occur in those phillipsite crystals from undersaturated basalt. The highest Si (up to 12.3 atoms per unit cell) and most alkali-rich come from replacement of rhyolitic pyroclastic sediment in saline environments.

	R²⁺ - R⁺ - Si and Na – Ca – K compositional diagrams of the phillipsite series analyses from Galli and Loschi Ghittoni (1972), Passaglia et al. (1990), and de'Gennaro et al. (1995). Red squares represent samples from cavities in basaltic rocks, and circles represent samples from diagenetically altered sedimentary rocks. Black circles represent samples from potassic pyroclastic rocks of Italy, the blue circles represent samples from saline, alkaline lake sediment, and the green circles represent samples from deep sea sediment. The four non-framework cations, K, Ca, Na, and Ba, show wide, but non-uniform variability. Of the three species, phillipsite-K is the most common, occurring in cavities of basaltic lavas and as a diagenetic alteration product in volcaniclastic sediment. In general the composition of phillipsite is controlled by the host rock, but the structure tends to fractionate K and Ba into the crystal. For example, compositions of phillipsite from deep sea sediment form a small field straddling the boundary between phillipsite-K and phillipsite-Na instead of reflecting the Na/K composition of sea water.

Occurences:
	Minerals of the phillipsite series occur in many different environments, including amygdaloidal filling of cavities in basaltic rocks and replacement of rhyolitic vitric tuff and welded tuff in terrestrial settings. They are an abundant authigenic constituent of deep sea sediment world-wide. Diagenesis of sediment and sedimentary rocks Reaction between the volcanic component of various kinds of sediment with interstitial water commonly produces authigenic zeolite minerals. In terrestrial accumulations of volcaniclastic sediment and rock, phillipsite minerals are alteration products in a variety of sediment types and soil in hydrologically closed systems and in thick sections of tephra and ignimbrite in hydrologically open systems. Generally phillipsite directly replaces glass shards in reactions with alkaline, saline waters. Hydrologically closed systems - tuff in lacustrine sediment. Lakes in closed basins with arid climates tend to become saline and alkaline. Zeolites are among the authigenic minerals to crystallize in this environment, especially as a replacement of vitric tuff incorporated into the lacustrine sediment. Phillipsite minerals, specifically phillipsite-Na and phillipsite-K, occurring in this type of environment at several localities in eastern California and western Nevada, USA, were first described by Hay (1964). Detailed descriptions of zeolite occurrences in lacustrine deposits of Pleistocene Lake Tecopa, California (Sheppard and Gude 1968), the Pliocene Big Sandy Formation, Arizona (Sheppard and Gude 1973), and the Miocene Barstow Formation, California (Sheppard and Gude 1969) soon followed. At Teels Marsh, western Nevada, Hay (1964) showed that rhyolitic tuff is actively reacting with alkaline pore water to form phillipsite, probably phillipsite-Na, within the upper 3 m of playa sediment. The phillipsite is associated with gaylussite, Na2Ca(CO3)2•5H2O, in the mud or with trona, Na3(CO3)(HCO3)•2H2O, efflorescence. Near the lake margin where salt efflorescence is thin or absent, the tuff shows little alteration. In later studies Mariner and Surdam (1970) showed that not only was an alkaline pH required by the reaction, but the Si content of the phillipsite is related to the pH of the reacting fluid. Taylor and Surdam (1981) show that alteration of the uppermost tuff to phillipsite at a depth of about 30 cm took about 1000 years. Field and petrographic studies of older lacustrine deposits of eastern California and Arizona (Sheppard and Gude 1968, 1969, and 1973) show that phillipsite-Na and phillipsite-K are abundant in this setting. Phillipsite may form monomineralic beds, or may be associated with clinoptilolite, erionite, chabazite, opal, potassium feldspar, and searlesite, NaBSi2O5(OH)2. These minerals tend to be located near the margins of the lake. For example, at Lake Tecopa, California, the zone containing phillipsite is between the fresh glass zone and the potassium feldspar zone in the center of the lake (Sheppard and Gude 1968). Phillipsite forms spherulites (about 0.2 mm across) of radially oriented fibers enveloping traces of the original glass shards. In some beds the phillipsite occurs as stubby, randomly oriented prisms. Some other occurrences of phillipsite in saline, alkaline lake deposits are Lake Natron, Kenya (Hay 1966); Lake Magadi, Kenya (Hay 1968, Surdam and Eugster 1976); Olduvai Gorge, Tanzania, Hay 1970); and Taylor Valley, Antarctica (Linkletter 1974).The phillipsite forming in these deposits is phillipsite-Na and has the highest Si contents of any natural phillipsite; TSi is about 0.75, (12 Si per unit cell). The high Si content is apparently controlled by the rhyolitic source material and by the pH of the reacting solution. Soils and surficial deposits. Most zeolites that occur in soils crystallize as a reaction between soil clay minerals or volcanic glass and saline, alkaline pore water. Soil zeolites, then, occur in those areas with tuffaceous soil, or in climates that develop alkaline soil water. The arid climate and evaporative pumping processes that can develop alkaline soils that are in some ways similar to hydrologically closed systems and tend to occur near saline, alkaline lakes, for example, the Peninj Beds on the west side of Lake Natron, Tanzania (Hay 1966). Reactions between meteoric water and strongly alkaline, basaltic pyroclastic deposits produce zeolites, including phillipsite, very near the ground surface. Because these reactions are more like those of hydrologically open systems, they are treated separately below. Soil occurrences of zeolite have been reviewed by Ming and Dixon (1988), Ming and Mumpton (1989), Boettinger and Graham (1995), and Ming and Boettinger (2001). Pedogenic phillipsite in soils from volcanic parent materials has been reported from Mississippi, USA (Raybon 1982), in former USSR (Travnikova et al. 1973), and Tanzania (Hay 1964, 1966, 1978). Hydrologically open systems. Terrestrial accumulations of pyroclastic debris, especially rhyolitic tephra and ignimbrite units, may alter to produce zeolites, in some cases phillipsite. Because the zeolites occur largely from reactions with through flowing vadose and groundwater, this type of process is called hydrologically open alteration (Hay and Sheppard 1977, Sheppard and Hay 2001). Most phillipsite formed in this way occurs from reactions between meteoric water and tuff with alkalic compositions, such as some phonolitic and tephritic tuff in Italy (Passaglia et al. 1990) and nephelinite tephra cones on Oahu, Hawaii (Hay and Iijima 1968). A different type of zeolitization is the “geoautoclave” mechanism, in which a hot, wet pyroclastic layer from a phreatomagmatic eruption is thought to trap a limited amount of condensed water during emplacement (Lenzi and Passiglia 1974). Reaction of heated water with alkali-trachyte to phonolite glass forms phillipsite and chabazite (Passaglia and Vezzalini 1985, Passaglia et al.. 1990, and Langella et al. 2001). Some examples, where abundant phillipsite may have formed in this manner, are the Eifel Tuff, Eifel District, Germany; the Campanian Ignimbrite and Neapolitan pozzolana, Italy; and the Tenerife ignimbrite units, Canary Islands (de’Gennaro et al. 1995; Langella et al. 2001). Phillipsite compositions from this type of alteration environment are strongly controlled by the composition of host pyroclastic rock. Most of the Italian occurrences are phillipsite-K. Deep Sea Sediment. Authigenic phillipsite is common in deep sea sediment of every ocean. It was first found by Murray and Renard (1891) in pelagic sediment associated with volcanic material in the central Pacific and Indian Oceans. In succeeding years phillipsite along with clinoptilolite and analcime has been repeatedly found in dredge and core sampling of ocean bottom sediment. With the advent of the Deep Sea Drilling Program at least some phillipsite has been found in the upper portions of almost every drill core taken from any ocean. Phillipsite occurs near the water-sediment interface to depths of several hundred meters. Crystals are colorless or pale yellow and range in size from 2 to 400 µm. Most are prismatic twins or twinned clusters, although Stonecipher (1978) reports some that appear to be single crystals. Most of the phillipsite occurrences are in fine-grained pelagic sediment such as brown clay, nanofossil ooze, calcareous ooze, and siliceous ooze, where it generally comprises 5 to 25% of the sediment. Commonly associated materials are clinoptilolite, palagonitic glass, smectite, iron and manganese oxides and hydroxides, and locally barite (Boles 1977). Authigenic phillipsite has been reported in manganese micro-nodules on the Bengal Fan (Chauhan et al. 1994) and as pseudomorphs of glass shards in manganese nodules from the Clarion-Clipperton area northeast equatorial Pacific Ocean (Lee and Lee 1998). The relationship between the relative abundance of clinoptilolite and phillipsite age (depth), reveals important aspects of the crystallization of these zeolites in deep sea sediment. Phillipsite nucleates readily and grows as burial proceeds. Growth periods have been estimated to be from 150,000 years (Czyscinski, 1973) to a million years (Bernat et al. 1970). However, the increasing in abundance into the Miocene Epoch suggests growth to at least 10 Ma. Phillipsite crystals in older sediment are generally etched, indicating dissolution (Kastner and Stonecipher 1978). Identification is by X-ray powder diffraction methods. Analyses by electron microprobe are difficult because the crystals are so small. Nonetheless, good analyses have been reported by Sheppard et al. (1970) and Stonecipher (1978). All samples that have been analyzed are phillipsite-K or phillipsite-Na with the compositional range straddling the boundary between the two species. Stonecipher (1978) concludes that a certain proportion of basaltic glass is essential for the formation of phillipsite. Although in some sediment, such as nanofossil ooze, all traces of volcanic material have disappeared, apparently with the crystallization of phillipsite (Bass 1976). Cavities in basaltic lavas. Phillipsite occurs in basalt cavities in many localities around the world. Some significant localities are: Aci Castello, Sicily and Capo di Bove and others near Rome, Lazio, Italy; Limberg (Betz 2005, Weisenberger and Spürgin, 2009), Annerod near Giessen, Hessen and Asbach, Westerwald, Germany; Giant’s Causeway, County Antrim, Ireland; Mazé, Niigata Prefecture, Japan; Melbourne area, Victoria, Australia; and in the U.S.A. at Wall Creek near Monument, Mount Vernon, Grant County, and Burnt Cabin Creek, Spray, Wheeler County, Oregon. Many others are listed and briefly described by Tschnerich (1992). The composition of the phillipsite is related in many cases to the composition of the host rock. The lowest TSi contents are those crystals formed in undersaturated lavas. The cation composition of the phillipsite is controlled to some extent by the host lava composition, such as phillipsite-K in the leucitite of Capo di Bove, but more importantly, early precipitated phases may deplete pore fluids in a major cation. For example, early calcite formation will greatly enhance the alkali content of phillipsite and other zeolites. In some occurrences an outside cation source will overwhelm the local fluid composition from decomposing glass. An example of the near phillipsite-Na end member occurs in a basalt flow underlying the sodium borate lake beds at Boron, California, USA (Wise and Kleck 1988). Common associated minerals are chabazite, analcime, thomsonite, natrolite, and many other zeolites and hydrated calcium silicates. Most occurrences are consistent with diagenetic or low temperature hydrothermal alteration of the host basalt. In zoned sequences, such as the Tertiary olivine-basalt section of eastern Iceland (Walker 1960), phillipsite occurs in the upper two zones. Compared to Icelandic geothermal areas the approximate temperature range of phillipsite formation is between about 65° and 85°C (Kristmannsdóttir and Tómasson 1978). Hydrothermal and deuteric alteration. Phillipsite has been found in several localities of hydrothermally altered oceanic crust. For example, Alt et al. (1998) show that phillipsite with smectite was produced by low temperature alteration of boninite and andesitic flows and breccia of the upper 700 m of forearcs in the western Pacific. Bölke et al. (1980) describe smectite and phillipsite-Na as products of alteration of pillow basalt in the North Atlantic. Phillipsite occurs rarely as a sparse late stage alteration product in some alkalic intrusions and pegmatite dikes. At Mont St. Hilaire, Quebec, rare phillipsite and/or harmotome occurs in eudialyte-rich pegmatite veins and sodalite xenoliths (Horváth and Galt, 1990). Barian phillipsite occurs with prehnite, calcite, and albite in an altered pegmatitic vein crossing serpentinite at Vezna western Moravia, Czech Republic (Černý 1960). Pekov (2000) reports several different occurrences of late stage phillipsite in the hydrothermal zones of pegmatoids in the Lovozero massif, Kola Peninsula, Russia. It was first found in a microcline pegmatite at Mannepakhk Mountain, and more recently in veinlets cutting lujavrite in Second Raslak Cirque, and in a microcline-aegerine zone of the “Bear’s Den” pegmatite in the Tyulbnyunuari river valley (Pekov 2000).

Uses:
	Significant deposits of sedimentary phillipsite occur in several countries, especially in Bulgaria, Hungary, Italy, Jordan, and the United States. Several of these have been exploited for industrial applications. Phillipsite-bearing tuff is being used to treat waste water, e.g. removal of ammonia and various heavy metals (Kallo 2001). Phillipsite is a major component of zeolitic tuff used as dimension stone in several countries, especially Italy (Colella et al. 2001).

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