Periodic Changes in the Rate of Electrochemical Release of Elements from Minerals, and Potential Geological Aspects of This Phenomenon

Issai Goldberg (isgoldberg@yahoo.com)

Level1/55 York Street NSW 2000 Sydney Australia, Australia

1. Experimental research on electrochemical dissolution of minerals in aqueous solutions, carried out 1975-90 in specially constructed cells, with stabilized electrical parameters and with a temperature of 22-25°. The ratio of solid to liquid was 4:1; the length of the process was up to 2000 hours.

2. Periodic changes were noted in the rate of release of the mineral-forming and trace elements from olivine, diopside, riebeckite, feldspar, quartz, calcite and fluorite. The change in the rate of release of elements into a solution is reflected in diagrams by non-linear (step-like kinetic) curves.

3. In order to explain the nature of this phenomenon a study was carried out of the parameters of the fluorite lattice during the dissolution process. An increase in the parameters of the lattice was found in the intervals of time when the rate of calcium release was decreased, while the lattice was compressed when the rate of calcium release was increased. Such synchronicity of processes could be explained by the migration of part of the calcium from inside the lattice to the solution.

4. That some of the ions are released from inside the mineral lattice and transferred to the solution is also confirmed by findings of experiments involving cleansing the minerals of any trace elements. Up to 80% of the trace elements can be released from the mineral, however the integrity of the lattice is maintained.

5. The kinetic curves can be presented as the formula: C (t) = C₁(t) + C₂ X [1-e^t(tau) / tg² (p¼t / t(tau))] Where C₁(t) = is the linear component of the dependence of the dissolved substance concentration from time, C= period, C₂ and t(tau) = the non-linear component.

6. Calculations have shown that the transfer of part of the elements from the inside the mineral lattice to the solution is associated with a release of energy that had been stored in the lattice. Such a cooperative process of a block of rocks could be the reason behind catastrophic phenomena in the earth, connected to explosive ejection of stored energy and matter. The author proposed a concentrated effort by experts towards investigating these phenomena.

The Crystal Chemistry of Alkali Amphiboles, Potassicferrisadanagaite and Ferrian Winchite, from Urals

Valeriya Gorbatova (vagor@mail.ru)¹, Elena Sokolova (guest@dsmp.unito.it), Julius Schneider (julius.schneider@ lrz.uni-muenchen.de)², Catherine McCammon (catherine.mccammon@uni-bayreuth.de)³ & Al'fred Bazhenov (john@ilmeny.ac.ru)⁴

¹ Dep. Crystallogr., Fac. Geology, Moscow State university, Moscow, Russia

² Inst. Kristallogr., Universitat Munchen, Munchen, Germany

³ Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, Germany

⁴ Mineralogica Institute, Miass, Russia

Potassicferrisadanagaite, ideal end-member KCa₂(Fe₃²⁺Fe₂³⁺) (Si₅Al₃)O₂₂(OH)₂, a silica-poor calcium amphibole of the edenite-hastingsite series (<5.5Si) and ferrian winchite, a silica-rich calcic-sodium amphibole, (CaNa)Mg₄(Al,Fe³⁺)Si₈O₂₂(OH)₂ have been found recently in a contact zone of the Ilmen alkaline massif, Ilmen Mountains, Southern Urals, Russia.

The crystal structures ( sp. gr. C2/m) of potassicferrisadanagaite a 9.9309(1), b 18.0949(3), c 5.3681(1) Å, ß 105.19(2)^o, Z = 2, D_(calc) = 3.36 g/cm³ and ferrian winchite, a 9.8339(2), b 18.0357(2), c 5.2974(1) Å, ß 104.195(1))^o, Z = 2, D_(calc) = 2.65 g/cm³ have been refined using the Rietveld method to the following values: R_p = 3.5 and 4.3%, R_F = 2.6 and 5.3%.

Mössbauer spectroscopy was used to characterize the Fe³⁺/(Fe²⁺ + Fe³⁺) ratio, IR spectroscopy was applied for characterization of short-range ordering (SRO), and site populations were assigned on the basis of the refined site-scattering values at the A-, B-, C-group sites. In contrast to a chemically homogenous potassicferrisadanagaite ferrian winchite samples reveal wide variations of chemical composition that complicates interpretation of the results obtained. For winchite similar heterogeneity has been previously described in literature.

For potassicferrisadanagaite structure in the presence of large amounts of ^TAl (>>2 apfu), linkage between the octahedral strip and the tetrahedral double-chain is maintained by incorporation of large cations at the M(1), M(2) and M(3) sites (Fe²⁺ for Mg, Fe³⁺ for Al) and maximal kinking of the tetrahedral double-chain (the latter being facilitated by K for Na at the A site). In the ferrian winchite Fe³⁺ (0.92 apfu) occurs at the M(2) site, <M(2)-O> distance is of 2.075 Å. ^TAl has been assigned to the T(1) site of the tetrahedral double chain.

Lattice-dynamical Calculations of Natrolite and its Instability Under Pressure

Sergei Goryainov¹ & Mikhail Smirnov²

¹ Institute of Mineralogy and Petrography, pr. Ak. Koptyuga, 3, 630090, Novosibirsk, Russia

² Institute for Silicate Chemistry, ul. Odoevskogo, 24, korp. 2, 199155, St. Petersburg, Russia

Recently frequencies and eigenvectors were calculated for some complex aluminosilicates (including garnets), but not for zeolites so far in view of their complex structure. There are only some attempts to calculate vibrations using selected blocks of unit cell. Thus, a consistent calculation of full set of zeolite vibrations remains urgent to elucidate thermodynamical properties controlled by lattice dynamics. Natrolite structure, the simplest one in zeolites, may be used as a model object for calculation of full set of vibrational modes and their comparison with observed polarized Raman and IR modes. Here the results of such calculation for primitive cell of natrolite Na₄[Al₄Si₆O₂₀]4H₂O are given: the determination of vibration forms and displacements of all atoms in the modes, including external modes of water molecules in the channels, the shift rate of vibration frequencies with pressure, elastic moduli and bulk modulus (K=47 GPa at zero pressure). Note, that natrolite structure has some advantage over other structures for understanding of the amorphization mechanism. The point is that natrolite, compressed in non-penetrating medium, shows no crystal phase transitions with increasing pressure. We observed only amorphization of the structure in large pressure range of 3-6 GPa. Pressure-dependent calculations using interatomic potentials with variable cell parameters permit to conclude that natrolite crystal structure loses its stability at about 5 GPa, which corresponds to the observed amorphization. This instability is connected with shear acoustic modes coupled with internal framework vibrations. According to our calculations these coupled internal modes present the displacements of Si(1) from C₂ symmetry axis and of oxygen atoms in Si(1)O₄, which strongly distort the tetrahedron. Moreover, instability of framework increases due to the effect of large static H₂O displacements increasing with pressure.