S. V. Goryainov

Pressure-induced over-hydration of thomsonite: A synchrotron powder diffraction study

Abstract The structural behavior of thomsonite compressed in aqueous medium up to 3 GPa was studied by means of in situ synchrotron powder diffraction with a diamond anvil cell. In the range between 0.0001 and 2 GPa, the compressibility of thomsonite is markedly lower than that reported previously, where a non-penetrating medium (with only 6% H2O) was used. This indicates a pressure-induced hydration (PIH), which results in the transition to an over-hydrated phase observed at 2 GPa. The structure of over-hydrated thomsonite contains one additional, half-occupied H2O position, coordinated by the calcium at the Ca2 site, with a scolecite-like coordination [CaO4(H2O)3]. The appearance of new H2O position causes a 4.5% volume expansion through the cooperative rotation of [T2O5]∞ chains, leading to the enlargement of the cross-section of the main channels parallel to c axis. The observed deformation mechanism is similar to that found in high-hydrated and super-hydrated natrolite, although only a half of the channels are affected by PIH. The present data indicate that the over-hydration effect in fibrous zeolites strongly depends on the partial water pressure in compressing medium.

Organic inclusions in salt. Part 3. Oil and gas inclusions in Cambrian evaporite deposit from East Siberia. A contribution to the understanding of nitrogen generation in evaporites

Abstract Halite in Cambrian KCl-deposits from the southern part of the Siberian platform, which have been thermally overprinted by dolerite intrusions, commonly contains inclusions dominantly composed of CO2 and less commonly, host inclusions composed of hydrocarbons. Four types of hydrocarbon inclusions have been identified in samples taken from locations devoid of dolerite intrusions. These are (1) monophase gaseous inclusions (i.e. N2, CH4 or N2–CH4), (2) aliphatic oil inclusions, (3) two-phase (L1+L2) hydrocarbon-brine inclusions and, (4) N2-hydrocarbon inclusions. The area where the N2-rich inclusions occur is associated with ammonium-free K-chlorides. By comparing different types of K-salt environments, the origin of the nitrogen could be identified. First, ammonium ions are produced by deamination of organic matter and stored in K-chlorides, and thereafter N2 is released from NH4–K-minerals by oxidation in zones rich in iron oxides and/or by 40K radiolysis.

Lattice dynamics and hydrostatic-pressure-induced phase transitions in ScF3

AbstractNew phase transitions induced by hydrostatic pressure in a cubic (under standard conditions) ScF3 crystal are discovered by the methods of polarization microscopy and Raman scattering. The space groups

Hydrostatic pressure-induced phase transitions in RbMnCl3: Raman spectra and lattice dynamics

R\bar 3c

A Raman Study of Hydrostatic Pressure Induced Phase Transitions in Rb 2 KInF 6 Crystals

for Z=2 and Pnma for Z=4 are proposed for the high-pressure phases. A nonempirical computation of the lattice dynamics of the crystal is carried out. It is shown that, under normal pressure, the cubic phase is stable down to T=0 K, while the application of a hydrostatic pressure gives rise to a phonon branch in the vibrational spectrum (between points R and M of the Brillouin zone) with negative values of squares of frequencies. The condensation of soft mode R5 at the boundary point of the Brillouin zone leads to rhombohedral distortion of the cubic structure with the unit cell volume doubling. The calculated frequencies at q=0 of the ScF3 lattice in the distorted rhombohedral phase are real-valued; the number and position of frequencies active in Raman scattering are in accord with the experimental values.

Structure and lattice dynamics of the high-pressure phase in the ScF3 crystal

Abstract Lime-monteponite solid solutions [(Ca,Cd)O ss] with 58.5–73.3 wt% CdO were discovered as an accessory phase in medium-temperature combustion metamorphic (CM) spurrite-fluorellestadite/ fluorapatite marbles from central Jordan. The type locality is situated in the northern part of the Siwaqa complex (Tulul Al Hammam area), the largest area of the “Mottled Zone” Formation in the Dead Sea region. The marbles were derived from bitumen-rich calcareous marine sediments of the Muwaqqar Chalk Marl Formation, which have high Cd, Zn, U, and Ni enrichments and contain Cd-rich wurtzite and sphalerite. Oxidative sintering of these sediments at 800–850 °C gave rise to unusual oxide accessories: lime-monteponite solid solutions, Cd-bearing Ca and Zn aluminate—tululite, zincite, and Zn-, Ni-, and Cu-rich periclase. Cadmium incorporation into different oxides was controlled by steric factors, while Cd[6] → Ca[6] was the principal isomorphic substitution. The intermediate members (Ca0.645Cd0.355)O–(Ca0.453Cd0.547)O with a halite-type structure have a cadmium incorporation ratio (KCd = Cdmineral/Cdrock) of about 843 and are the main sites for cadmium in CM marbles. In supergene environments, at low water/rock ratios, (Ca1−xCdx)(OH)2 ss (x ≤ 0.5) constitute the main secondary phase after (Ca,Cd)O ss. At higher water/rock ratios and in the presence of Cl− and F− in the solutions, calcium, and cadmium precipitated as separate phases ﹛fluorite (CaF2) and basic cadmium chloride [Cd(OH)2–xClx)]﹜. A part of cadmium becomes retained in calcium silicate hydrates. The common occurrence of anhydrous (Ca,Cd)O grains in natural rocks, only partly altered to (Ca,Cd)-hydroxide after at least 100 ka exposure to weather and climate, proves that both phases are effective long-term Cd immobilizers.

Behavior of natrolite zeolite and fluorapatite at high pressures in a water medium

Raman scattering spectra of RbMnCl3 are measured at room temperature under high hydrostatic pressure. The results are interpreted based on first principles lattice dynamics calculations. The experimental data obtained correlate with the calculations in the low frequency domain but disagree slightly in the region of high-frequency vibrations. The transition from the hexagonal to the cubic perovskite phase observed earlier (near 0.7 GPa) was confirmed, and new transitions to lower symmetry distorted phases were discovered (at 1.1 and 5 GPa).

Raman investigation of fibrous zeolites of the natrolite group at high pressures of an aqueous medium

Abstract The elastic and structural behavior of natural cordierite compressed in aqueous medium up to 6 GPa was studied by means of in situ synchrotron powder diffraction with a diamond-anvil cell. In the range between 1-4 GPa the elastic behavior is regular and slightly anisotropic, with linear compressibilities βa:βb:βc = 4:4:5, the most rigid a-b plane coinciding with the orientation of 6-membered rings. A distinct decrease of compressibility in the range of 4-5 GPa indicates a pressure-induced hydration (PIH), which is confirmed by the structure refinements. The addition of about 60% of the initial water content into the cordierite channels proceeds through positional disordering of the H2O sites inside the channel cavity and a stepwise filling of the H2O position inside the 6-membered rings, leading to the phase transition at about 4.7 GPa. The appearance of H2O molecules inside 6-membered rings prevents their contraction and even causes their slight enlargement along the a direction, apparently related to the orientation of H-bonds. This results in an anisotropic deformation of the unit cell and an increase of the a parameter in the HP phase at 4.9 GPa, as well as a decrease of linear compressibility along a upon the further compression up to 6 GPa (βa:βb:βc = 5:9:10).