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The structural evolution of yugawaralite |Ca 1.93 Na 0.08 (H 2 O) 8.1 |[Al 3.94 Si 12.06 O 32 ], space group Pc , a = 6.72309(15), b = 13.9990(2), c = 10.0477(2) Å, β = 111.164(2)°, V = 881.87(3) Å3, compressed in penetrating (ethanol:water 4:1) and non-penetrating (paraffin oil) media, was studied up to 3.2 GPa. Under the compression in a penetrating medium, yugawaralite experiences pressure-induced hydration. Additional H 2 O molecules occupy two positions which do not enter the coordination of the extra-framework cations: one of them is partially filled under ambient conditions, and the second is initially vacant. At around 2 GPa, yugawaralite experiences a phase transition with doubling of the a - and b -parameters of the unit cell. At high pressure the diffraction frames contain sharply broadened low-intensity diffuse reflections corresponding to a multiple increase of the unit cell metric. The structure of the high-pressure phase solved in the sub-cell, corresponding to the initial metric, is characterized by the disordering of the framework sub-chains in which the SiO 4 -tetrahedra become alternatively oriented. The pressure-induced structural changes are completely reversible. The compression of yugawaralite in a non-penetrating medium does not lead to radical structural changes. The structure symmetry is preserved; there are no signs of diffuse scattering or the splitting of atomic positions. [Display omitted] • Structural evolution of yugawaralite was studied under in situ high- P conditions. • In a penetrating medium, yugawaralite experiences pressure-induced hydration. • A new phase with a disordered framework was detected near 2 GPa. [ABSTRACT FROM AUTHOR]

Hydrothermal zeolites (laumontite, yugawaralite, analcime, heulandite, clinoptilolite), prehnite and pumpellyite have been recognised in a succession of volcanic, autoclastic, pyroclastic, resedimented volcaniclastic and mixed siliciclastic–volcaniclastic deposits. In cone-building lithofacies association attaining 310 m, the alteration minerals commonly change within a single normally graded depositional unit or alternate in the section on a dm- to m-scale, according to the host-rock lithofacies. Fine-grained deposits rich in juvenile glassy pyroclasts are altered to heulandite and clinoptilolite or analcime, and laumontite widely occurs in coarse-grained host-rocks (lapilli tuff, hyaloclastite breccia, volcaniclastic breccia, hyaloclastites) and fracture systems. In near-vent lithofacies association attaining 420 m, prehnite–laumontite, laumontite–analcime, and laumontite–heulandite–clinoptilolite zones developed as a result of superimposed thermal regime generated by the emplacement of an over 200 m thick sill. The recognised dependence of alteration on porosity, permeability and fracturing of the host-rock is closely related to hydrological conditions in the stratovolcano-hosted hydrothermal system with convective–advective flow regime. After separation of steam and gases from convecting hydrothermal fluids, denser liquids outflowed intermittently, preferentially through steeply inclined (20–30°) high-permeability layers in the stratovolcano edifice. In low-permeability layers the flow was slow and thermal conditions were mainly attained by conduction. Zeolites developed only in coarse- and fine-grained vitroclastic tuffs, presumably by the dissolution of volcanic glass. The interstratified siliciclastic siltstones, tuffites and resedimented deposits with low content of glassy particles are devoid of zeolites and indicate compositional constraint on zeolitisation. Lava flows, cooling in a submarine environment and undergoing disintegration and mingling with the enclosing water-saturated sediment were individual, ephemeral and spatially localised high-temperature hydrothermal systems favourable for the formation of pumpellyite, prehnite and laumontite. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) was used to characterize the morphological and cleavage surfaces in a number of natural zeolites. The investigated zeolites (stilbite, heulandite, thomsonite, yugawaralite, laumontite, and a few others) show rather interesting and sample-dependent microtopographical features related to the mechanisms involved in the surface growth processes at the molecular level. The results obtained by AFM on stilbite, heulandite, and yugawaralite during the preliminary surface characterization are presented, and the images show that molecular resolution can be achieved and crystallographically interpreted by careful preparation of the sample. [Copyright &y& Elsevier]