Giovanna Vezzalini

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.

The crystal structure refinement of a natural mordenite

AbstracL The crystal structure of natural mordenite from Elba (Italy) with chemical formula (Nai.49K2.8oMgo.o4Ca2.osSro.osXAl8.98Si39.i3)096 • 29.07HjO was refined in its hydrated form up to a wR value of Si2%. Systematic absences were consistent with the Cmcm space group but the asymmetry of the extraframework ions indicated as more probable the acentric subgroup Cmc2i. Consequently the atom 08 is no longer set on an inversion center and the T—08—T angle is not constrained to 180°. The Si/Al distribution is partially ordered, with an enrichment of AI in the tetrahedra of the four-membered ring. All Ca ions are localized in a eightcoordinated site; K ions altemate with water molecules in a six-coordinated Site.

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.

Structural deformation mechanisms of zeolites under pressure

Abstract The HP behavior of the natural zeolite yugawaralite and of the synthetic zeolite Na-A was studied by in situ synchrotron X-ray powder diffraction, using a non-penetrating P-transmitting medium. The unit-cell parameters of yugawaralite were refined up to the pressure of 10 GPa, at which reductions were found of about 7, 2.4, 7, 1.3, and 15% for a, b, c, β, and V, respectively. Contractions of 6.5 and 18.4% were found for a and V, respectively, for zeolite Na-A in the range 10-4 to 6.8 GPa. Diffraction patterns collected during decompression show that the effects induced by high pressure on both samples are almost completely reversible. These results are compared with those obtained under similar experimental conditions for other natural zeolites, with the aim of rationalizing the deformation mechanisms of these porous materials and comparing their flexibility under high-pressure and high-temperature conditions.

High-pressure behavior of bikitaite: An integrated theoretical and experimental approach

Abstract Pressure-induced structural modifications in the zeolite bikitaite are studied by means of in situ synchrotron X-ray powder diffraction and ab initio molecular dynamics. The experimental cell parameters were refined up to 9 GPa, at which pressure we found reductions of 4.5, 4.5, 6.3, and 15% in a, b, c, and V, respectively. Minor variations were observed for the cell angles. Complete X-ray amorphization is not achieved in the investigated P range, moreover the P-induced effects on the bikitaite structure are completely reversible. Because it was possible to extract only the cell parameters from the powder patterns, the atomic coordinates at 5.7 and 9.0 GPa were obtained by means of Car-Parrinello simulations using the unit-cell parameters experimentally determined at these pressures. Analysis of the computational results for increasing pressures showed that the volume contraction is essentially due to rotations of the tetrahedra; the 8-ring channels become more circular; the pyroxene chain becomes more corrugated in the b-c plane; and the mean Li-O bond distances and coordination polyhedral volumes decrease with increasing pressure without significant distortion of the internal angles. The peculiar aspect of the bikitaite structure, i.e., the presence in the channels of a “floating” one-dimensional water chain, is only partially maintained at high pressure; the compression brings framework O atoms close enough to water hydrogen atoms to allow the formation of host-guest hydrogen bonds, without, however, destroying the one-dimensional chain.

Structural modifications induced by dehydration in the zeolite gismondine

Abstract Gismondine from Montalto di Castro, Italy [Ca3.91Al7.77Si8.22O32·17.57 H2O], a = 10.0199(4), b = 10.6373(5), c = 9.8316(5) A , β = 92.561(6)°, space group P21/c, dehydrated in vacuum for 1 and 24 h and transformed into two new phases, here called gismondine (1 h) and gismondine (24 h), respectively. Gismondine (1 h) is characterized by 9.5% water loss and by a small decrease in the cell volume (ΔV = 0.6%); cell parameters are a = 9.989(3), b = 10.616(3), c = 9.820(3) A , and β = 92.57(2)°. The framework is almost undistorted, but a rearrangement of water molecules causes a change in space group to P21, with formation of a more regular 6-coordinated Ca polyhedron. The final Rw value (isotropic displacement factors) is 7.6%. Gismondine (24 h) is characterized by the orthorhombic space group P212121 and a unit cell doubled with respect to the nondehydrated sample; cell parameters are a = 13.902(9), b = 8.892(4), and c = 13.952(5) A . More than 50% of water is lost, the framework is highly distorted, and the channels are strongly squashed. Residual water sites are fully occupied. Ca polyhedra are seven-fold coordinated and are linked by vertices to form infinite chains. The final Rw value (isotropic displacement factors) is 7.6%.

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.

The “template” effect of the extra-framework content on zeolite compression: The case of yugawaralite

Abstract The microscopic behavior of the Ca-zeolite yugawaralite has been studied by ab initio molecular dynamics simulations adopting experimental cell parameters obtained at pressures up to ~9 GPa. Pressure-induced volume contraction occurs via rotations of quasi-rigid TO4 tetrahedra that reduce the size of the channels in which the extra-framework species are located. Such rotations are governed by deformation of the coordination polyhedron of Ca, which is made up of water and framework O atoms. Contraction of the Ca-H2O distances is favored at moderate pressure; at higher pressure the shortening of Ca-framework O atom distances becomes prevalent. The hydrogen bond network plays a fundamental role in the overall response to pressure. Our results indicate that the high-P-induced deformation of the framework structure is strictly correlated to the extra-framework species that act as “templates” in the compression process.

High-pressure deformation mechanism in scolecite: A combined computational-experimental study

Abstract Pressure-induced structural modifications in scolecite were studied by means of in situ synchrotron X-ray powder diffraction and density functional computations. The experimental cell parameters were refined up to 8.5 GPa. Discontinuities in the slope of the unit-cell parameters vs. pressure dependence were observed; as a consequence, an increase in the slope of the linear pressure-volume dependence is observed at about 6 GPa, suggesting an enhanced compressibility at higher pressures. Weakening and broadening of the diffraction peaks reveals increasing structural disorder with pressure, preventing refinement of the lattice parameters above 8.5 GPa. Diffraction patterns collected during decompression show that the disorder is irreversible. Atomic coordinates within unit cells of different dimensions were determined by means of Car-Parrinello simulations. The discontinuous rise in compressibility at about 6 GPa is reproduced by the computation, allowing us to attribute it to re-organization of the hydrogen bonding network, with the formation of water dimers. Moreover we found that, with increasing pressure, the tetrahedral chains parallel to c rotate along their elongation axis and display an increasing twisting along a direction perpendicular to c. At the same time, we observed the compression of the channels. We discuss the modification of the Ca polyhedra under pressure, and the increase in coordination number (from 4 to 5) of one of the two Al atoms, resulting from the approach of a water molecule. We speculate that this last transformation triggers the irreversible disordering of the system.