Ermanno Galli

Recommended nomenclature for zeolite minerals: report of the subcommittee on zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names

Abstract This report embodies recommendations on zeolite nomenclature approved by the International Mineralogical Association Commission on New Minerals and Mineral Names. In a working definition of a zeolite mineral used for this review, interrupted tetrahedral framework structures are accepted where other zeolitic properties prevail, and complete substitution by elements other than Si and Al is allowed. Separate species are recognized in topologically distinctive compositional series in which different extra-framework cations are the most abundant in atomic proportions. To name these, the appropriate chemical symbol is attached by a hyphen to the series name as a suffix except for the names harmotome, pollucite and wairakite in the phillipsite and analcime series. Differences in space- group symmetry and in order-disorder relationships in zeolites having the same topologically distinctive framework do not in general provide adequate grounds for recognition of separate species. Zeolite species are not to be distinguished solely on Si : Al ratio except for heulandite (Si : Al < 4.0) and clinoptilolite (Si : Al ≥ 4.0). Dehydration, partial hydration, and over-hydration are not sufficient grounds for the recognition of separate species of zeolites. Use of the term ‘ideal formula’ should be avoided in referring to a simplified or averaged formula of a zeolite. Newly recognized species in compositional series are as follows: brewsterite-Sr, -Ba; chabazite-Ca, - Na, -K; clinoptilolite-K, -Na, -Ca; dachiardite-Ca, -Na; erionite-Na, -K, -Ca; faujasite-Na, -Ca, -Mg; ferrierite-Mg, -K5 -Na; gmelinite-Na, -Ca, -K; heulandite-Ca, -Na, -K5 -Sr; levyne-Ca, -Na; paulingite- K, -Ca; phillipsite-Na, -Ca, -K; stilbite-Ca, -Na. Key references, type locality, origin of name, chemical data, IZA structure-type symbols, space-group symmetry, unit-cell dimensions, and comments on structure are listed for 13 compositional series, 82 accepted zeolite mineral species, and three of doubtful status. Herschelite, leonhardite, svetlozarite, and wellsite are discredited as mineral species names. Obsolete and discredited names are listed.

Position of cations and water molecules in hydrated chabazite. Natural and Na-, Ca-, Sr- and K-exchanged chabazites

Crystal structures of natural and hydrated Na, Ca, Sr and K-exchanged chabazite from Keller (Germany) were refined at room temperature in the R 3 m space group. The most probable distribution of ions indicates the presence of four cation sites; one at the centre of the hexagonal prism, two in the large cage along the [111] diagonal, and the fourth near the 8-ring window which is split into two sites close to each other in the monovalent exchanged forms. The site at the centre of the D 6 R is empty in the Na and K-exchanged chabazites. In this last form one of the two sites along [111] is also empty. Water molecules are spread over a large number of sites, one with 100% occupancy, at the centre of the 8-ring window, the others, normally with low occupancy, inside the large cage. Occupancies of both cation and water molecule sites vary greatly in the different forms.

Crystal structure of the zeolite mutinaite, the natural analog of ZSM-5

We describe the crystal structure of the high-silica zeolite mutinaite, recently found at Mt. Adamson (Northern Victoria Land, Antarctica). Mutinaite is the natural counterpart of the synthetic zeolite ZSM-5. The new mineral, (Na 2.76 K 0.11 Mg 0.21 Ca 3.78 ) (Al 11.20 Si 84.91 ) · 6O H 2 O H 2 O, is orthorhombic, space group Pnma, with a = 20.201(2), b = 19.991(2), and c = 13.469(2) A. A single-crystal X-ray diffraction experiment was performed at the synchrotron radiation source ESRF (Grenoble). No Si-Al order in the framework has been detected. Large distances between ions in the channels and framework oxygens suggest weak interactions between the framework and extraframework species.

Mutinaite, a new zeolite from Antarctica: The natural counterpart of ZSM-5

Mutinaite is the third new zeolite from Ferrar dolerites at Mt. Adamson (Northern Victoria Land, Antarctica). The mineral occurs as subspherical aggregates of tiny radiating lath-like fibres or as aggregates of transparent, colourless to pale-milky, tiny tabular crystals; it has vitreous luster, white streak and good 100 cleavage. Mutinaite is brittle with d meas = 2.14(3) and d calc = 2.17 g/cm 3 . Optically, it is biaxial negative with α = 1.485(2), β = 1.487(2) and γ = 1.488(2). The orientation is X = b, Y = a, Z = c. Mutinaite is orthorhombic with a = 20.223(7), b = 20.052(8), c = 13.491 (5)A, space group Pnma. The strongest powder X-ray diffraction lines are (d(A), I, hkl): 11.20, 84, 101, 011; 9.98, 35, 200,020; 3.85, 100, 501, 051; 3.75, 98, 303; 3.67, 27, 133; 3.00, 32, 503. The framework topology is that of the synthetic zeolite ZSM-5. The chemical formula is: (Na 2.76 K 0.11 Mg 0.21 Ca 3.78 ) Σ = 6.86 (Al 11.20 Si 84.91 ) Σ=96.11 O 192 · 60H 2 O. The Si/Al ratio, equal to 7.6, is the highest found in a natural zeolite. Thermal stability and rehydration capacity are very high. The name is from Mutina, the ancient Latin name of the city of Modena.

A new occurrence of katoite and re-examination of the hydrogrossular group

A new occurrence of katoite (Ca2.95Fe0.03A12.03(SiO4)1.12(OH)7.51; a = 12.286) found near Dunabogdany (Hungary), along with its structural refinement is reported here. The crystal-chemical data, the physical properties, and the structure refinement of this new member of the Ca3Al2(SiO4)3-Ca3Al2(O4H4)3 series indicate the presence of about 37% grossular. The positional disorder of the oxygen atom, a peculiar feature of the hydrogarnet structure, is described here in terms of both anisotropy along the d-O vector, and presence of two distinct oxygen sites (unsplit- and split-O models, respectively). The hydrogen atom was localised for both models in the difference Fourier map. The structural features of the katoite from Dunabogdany are compared with those of other hydrogrossulars and with the two end-members “anhydrous” grossular, and Si-free katoite. The results of the unsplit-O model refinement confirm the increase of the tetrahedron volume with the substitution of Si by 4H+. The geometry of the coordination polyhedra in the two configurations resulting from the split-O model are also discussed. This second model better describes from the crystallochemical point of view the substitution of Si4+ with 4H+ in the tetrahedra. However, the tetrahedra of the two dimensions are randomly distributed in the unit cell and hence domains of the two end-member configurations are not expected in katoite structure. This conclusion is also strengthened by the TEM study of katoite from Dunabogdany.**

Chromium-containing muscovite crystal chemistry and XANES spectroscopy

To verify chromium enrichment of the muscovite layer, a crystal chemical and XANES study on chromium-containing muscovite crystals from the South Island of New Zealand was carried out. The crystals studied differ from those of end-member muscovite in that they display variable levels of octahedral substitutions and homovalent and heterovalent substitution of K in interlayer sites. Single-crystal X-ray diffraction data were collected for three crystals in the space group C 2/ c to an agreement factor (R obs ) from 0.025 to 0.033. Tetrahedral cation disorder was found for each sample and the values of mean bond length for both tetrahedra do not depart significantly from that of the end-member muscovite-2 M 1 . Electron density at the M2 site is greater than that required for the ideal muscovite-2 M 1 structure, and a small excess of electron density is found for two crystals in M1. As the octahedral substitution of larger cations for Al increases in the octahedral sites, the match between tetrahedral and octahedral sheets improves and tetrahedral rotation angle, α, decreases. XANES spectra at the Cr K-edge in these chromium-containing muscovite samples exhibit octahedral symmetry. Moreover, a careful analysis of the pre-edge region shows at least two features. A qualitative fitting procedure of the pre-edge region indicates that no more than 0.5% of total Cr(III), if any, may occupy the tetrahedral site.

A reexamination of the crystal structure of erionite

The crystal structure of a natural erionite from Nizhnyaya Tunguska, Siberia (schematic formula K 2 Ca 3.5 Al 9 Si 27 O 72 · 32H 2 O) has been refined to a residual wR of 0.044. The erionite framework can be described by a sequence AABAAC … of 6-membered rings of tetrahedra. The (Si, Al) distribution (24% of Al in T1 and 31% of Al in T2) is consistent with the strong disorder found in tetrahedral sites for all zeolites describable by a sequence of 6-rings. Erionite, as in the closely related zeolite offretite, shows a slight enrichment of Al in the single 6-ring. K is at the center of the cancrinite cage and coordinates 6 framework oxygen atoms. Ca atoms alternately occupy three sites, quite near each other, on the triad axis parallel to c , at the center of the erionite cage. Their coordination number varies between 6 and 9. The marked differences in T—O distances found between hydrated and dehydrated erionite are explained in terms of interactions between extraframework ions and framework oxygens.

Crystal structure refinement of aluminian lizardite-2H 2

Abstract Well-crystallized euhedral crystals of aluminian lizardite-2H2 (Mg2.35Fe2+0.06Fe3+0.07Al0.52) (Si1.41Al0.59)O5.00(OH)4.00 were found near Schio (Vicenza, Italy). To gain insight into the role of a high Al content lizardite, chemical analyses and single-crystal X-ray data collection were conducted. Structure refinement, completed in space group P63 (agreement factor R = 0.034), gives mean T-O values of 1.654 Å and 1.664 Å for T1 and T2 sites, respectively. The ditrigonal distortion of the six-membered tetrahedral ring is positive (α = +9.7°), as expected for the 2H2 polytype. The octahedral site has a mean bond length similar to that of the Mg-rich octahedra of amesite and distortion parameters similar to those of Al-rich octahedra.

A reexamination of the crystal structure of the zeolite offretite

The crystal structure of a natural offretite from Poia Creek, Adamello, Italy (schematic formula KCaMgAl 5 Si 13 O 36 :17 H 2 O) has been refined to a residual wR of 0.038. The offretite framework can be described by a sequence AABAAB … of 6-membered rings of tetrahedra. The (Si,Al) distribution (29% of AI in T1 and 37% of AI in T2) is consistent with the disorder found in tetrahedral sites for ail zeolites describable by sequences of 6-rings. K is at the center of the cancrinite cage and is coordinated to 6 framework oxygen atoms. Mg, placed at the center of the gmelinite cage, is coordinated to 6 water molecules; 4 of these are disordered on 9 possible positions relative to two sites with multiplicity 6 and 3, respectively. Ca atoms alternately occupy two sites near each other, at the center of the wide channel parallel to parameter c, and are octahedrally coordinated to the same water molecules. The strong differences in the T−O distances found between hydrated and dehydrated offretite are here explained in terms of interactions between extraframe-work ions and framework oxygens.

Terranovaite from Antarctica: A new 'pentasil' zeolite

Abstract A new high-silica zeolite, terranovaite, was recently found in cavities of Ferrar dolerites at Mt. Adamson (Northern Victoria Land, Antarctica). The mineral [(Na4.2K0.2Mg0.2Ca3.7)Σ8.3(Al12.3Si67.7)Σ80.0O160 · > 29 H2O] occurs as globular masses that flake off in transparent lamellae; it has a vitreous luster, white streak, {010} perfect cleavage, and {001} distinct parting. The observed density is 2.13 ± 0.02 g/cm3. Optically, it is biaxial positive, with 2V = 65°, α = 1.476, β = 1.478, γ = 1.483 (all ± 0.002). The orientation is X = c, Y = a, and Z = b. Terranovaite is orthorhombic with a = 9.747(1), b = 23.880(2), c = 20.068(2) Å and topological symmetry Cmcm. The strongest powder X-ray diffraction lines are (d (Å), I, hkl ): 11.94,40,020; 10.16,65,021,002; 9.04,33,110; 3.79,100,025,240; 3.61,40,153. Terranovaite topology, hitherto unknown in either natural or synthetic zeolites, is characterized by the presence of pentasil chains and of a twodimensional ten-membered ring channel system. The mineral was named terranovaite after the Italian Antarctic Station at Terranova Bay, Antarctica.