Abstract
A model for the modulated crystal structure of an antigorite polysome with m = 16 (where m is related to the number of tetrahedra spanning a wavelength along a) was refined by single-crystal synchrotron diffraction data in C2/m, using crystals coexisting with the m = 17 polysome from Val Malenco, Italy, which was previously determined structurally. Lattice parameters [a = 81.664(10), b = 9.255(5), c = 7.261(5) Å, β = 91.409(5)°] were determined using a single-crystal diffractometer equipped with an area detector at the Desy synchrotron (Hamburg). The structure was solved by direct methods, and the model refined using 19 222 symmetry-related reflections. The final R4σ factor was 0.0951, calculated for 7246 reflections.
The structure of the m = 16 antigorite polysome strongly resembles that of the m = 17 polysome. A continuous, wavy octahedral sheet is linked to a tetrahedral sheet, reversing its polarity through sixfold tetrahedral and eightfold tetrahedral rings. The half-wave has a curvature radius of 80.1 Å. Polyhedral geometry, ditrigonalization angles, and interlayer O-O distances are similar in the two polysomes. The only differences concern the number of tetrahedra for the m = 16 polysome (an even number which leads to symmetric half-waves) and the periodic b/2 shift involving the eightfold rings (to produce the doubling of the a parameter and a C-centered cell).
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Presidential Address: Elastic properties of minerals and the influence of phase transitions
- Pressure-induced hydration in zeolite tetranatrolite
- Annealing experiments on induced fission tracks in apatite: Measurements of horizontal-confined track lengths and track densities in basal sections and randomly oriented grains
- Alpersite (Mg,Cu)SO4·7H2O, a new mineral of the melanterite group, and cuprian pentahydrite: Their occurrence within mine waste
- Application of a new vanadium valence oxybarometer to basaltic glasses from the Earth, Moon, and Mars
- Quantitative polarized infrared analysis of trace OH in populations of randomly oriented mineral grains
- Hydrogen incorporation in olivine from 2–12 GPa
- A numerical model for steady-state temperature distributions in solid-medium high-pressure cell assemblies
- Thermodynamics and kinetics of cation ordering in natural and synthetic Mg(Al,Fe3+)2O4 spinels from in situ high-temperature X-ray diffraction
- Kinetics of cation ordering in natural Mg(Al,Cr3+)2O4 spinels
- Equations of state and structures of andalusite to 9.8 GPa and sillimanite to 8.5 GPa
- Equation of state and phase transition in KAlSi3O8 hollandite at high pressure
- A novel arrangement of silicate tetrahedra in the uranyl silicate sheet of oursinite, (Co0.8Mg0.2)[(UO2)(SiO3OH)]2(H2O)6
- Aluminum substitution in stishovite and MgSiO3 perovskite: High-resolution 27Al NMR
- The effect of chlorine on the viscosity of Na2O-Fe2O3-Al2O3-SiO2 melts
- TEM imaging and analysis of microinclusions in diamonds: A close look at diamond-growing fluids
- A partial molar volume for ZnO in silicate melts
- Garnet-spinel intergrowths in ultrahigh-temperature granulite, Eastern Ghats, India: Possible evidence of an early Tschermak-rich orthopyroxene during prograde metamorphism
- The partial molar volume of Fe2O3 in alkali silicate melts: Evidence for an average Fe3+ coordination number near five
- The crystal structure of a second antigorite polysome (m = 16), by single-crystal synchrotron diffraction
- Oxide melt solution calorimetry of sulfides: Enthalpy of formation of sphalerite, galena, greenockite, and hawleyite
- An experimental determination of the effect of pressure on the Fe3+/ΣFe ratio of an anhydrous silicate melt to 3.0 GPa
- Evolution of product phase assemblages during thermal decomposition of muscovite under strong disequilibrium conditions
- Synthetic P21/m amphiboles in the system Li2O-Na2O-MgO-SiO2-H2O (LNMSH)
- Incongruent dissolution of wollastonite measured with vertical scanning interferometry
- Experiments on CaCO3-MgCO3 solid solutions at high pressure and temperature
- Calorimetric data for naturally occurring magnesiocarpholite and ferrocarpholite
- Clinopyroxene exsolution in wollastonite from Namaqualand granulite, South Africa
- Icosahedral coordination of phosphorus in the crystal structure of melliniite, a new phosphide mineral from the Northwest Africa 1054 acapulcoite
- Mechanism for the dissolution of olivine series minerals in acidic solutions
- High-pressure behavior of synthetic antigorite in the MgO-SiO2-H2O system from Raman spectroscopy
- Sinoite (Si2N2O) shocked at pressures of 28 to 64 GPa
- Laser Raman spectroscopic measurements of water in unexposed glass inclusions
- The Mars/Earth dichotomy in Mg/Si and Al/Si ratios: Is it real?
- Equation of state of CaIrO3-type MgSiO3 up to 144 GPa
- Synchrotron infrared spectroscopy of synthetic Na(NaMg)Mg5Si8O22(OH)2 up to 30 GPa: Insight on a new high-pressure amphibole polymorph