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  • 1
    Electronic Resource
    Electronic Resource
    Comparative compressibilities of majorite-type garnets (1994)
    Springer
    Physics and chemistry of minerals 21 (1994), S. 344-349 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Relative compressibilities of five silicate garnets were determined by single-crystal x-ray diffraction on crystals grouped in the same high-pressure mount. The specimens include a natural pyrope [(Mg2.84Fe0.10Ca0,06) Al2Si3O12], and four synthetic specimens with octahedrally-coordinated silicon: majorite [Mg3(MgSi)Si3O12], calcium-bearing majorite [(Ca0.49Mg2.51)(MgSi)Si3012], sodium majorite [(Na1.88Mgp0.12)(Mg0.06Si1.94)Si3O12], and an intermediate composition [(Na0.37Mg2.48)(Mg0.13Al1.07 Si080) Si3O12]. Small differences in the compressibilities of these crystals are revealed because they are subjected simultaneously to the same pressure. Bulk-moduli of the garnets range from 164.8 ± 2.3 GPa for calcium majorite to 191.5 ± 2.5 GPa for sodium majorite, assuming K′=4. Two factors, molar volume and octahedral cation valence, appear to control garnet compression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202099
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  • 2
    Electronic Resource
    Electronic Resource
    Phase E: A high pressure hydrous silicate with unique crystal chemistry (1993)
    Springer
    Physics and chemistry of minerals 19 (1993), S. 357-360 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The unique cation-disordered crystal structures of two samples of phase E, a non-stoichiometric, hydrous silicate synthesized in a uniaxial, split-sphere, multi-anvil apparatus at conditions above 13 GPa and 1000° C, have been solved and refined in space group $$\bar 3$$ . The compositions and unit cells for the two materials, assuming six oxygens per cell, are Mg2.08Si1.16H3.20O6, a=2.9701(1) Å, c=13.882(1) Å V = 106.05(4) Å3 for sample 1, and Mg2.17Si1.01H3.62O6, a=2.9853(6) Å, c=13.9482(7) Å, V= 107.65(4) Å3 for sample 2. The structure contains layers with many features of brucite-type units, with the layers stacked in a rhombohedral arrangement. The layers are cross linked by silicon in tetrahedral coordination and magnesium in octahedral coordination, as well as hydrogen bonds. Interlay er octahedra share edges with intralayer octahedra. Interlayer tetrahedra would share faces with intralayer octahedra. To avoid this situation, there are vacancies within the layers. There is, however, no long-range order in the occupation of these sites, as indicated by the lack of a superstructure. Selected-area electron diffraction patterns show walls of diffuse intensity similar in geometry and magnitude to those observed in short-range-ordered alloys and Hågg phases. Phase E thus appears to represent a new class of disordered silicates, which may be thermodynamically metastable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202972
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  • 3
    Electronic Resource
    Electronic Resource
    Compressibility and crystal structure of sillimanite, Al2SiO5, at high pressure (1997)
    Springer
    Physics and chemistry of minerals 25 (1997), S. 39-47 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The unit-cell dimensions and crystal structure of sillimanite at various pressures up to 5.29 GPa have been refined from single-crystal X-ray diffraction data. As pressure increases, a and b decrease linearly, whereas c decreases nonlinearly with a slightly positive curvature. The axial compression ratios at room pressure are βa:βb:βc=1.22:1.63:1.00. Sillimanite exhibits the least compressibility along c, but the least thermal expansivity along a (Skinner et al. 1961; Winter and Ghose 1979). The bulk modulus of sillimanite is 171(1) GPa with K′=4 (3), larger than that of andalusite (151 GPa), but smaller than that of kyanite (193 GPa). The bulk moduli of the [Al1O6], [Al2O4], and [SiO4] polyhedra are 162(8), 269(33), and 367(89) GPa, respectively. Comparison of high-pressure data for Al2SiO5 polymorphs reveals that the [SiO4] tetrahedra are the most rigid units in all these polymorphic structures, whereas the [AlO6] octahedra are most compressible. Furthermore, [AlO6] octahedral compressibilities decrease from kyanite to sillimanite, to andalusite, the same order as their bulk moduli, suggesting that [AlO6] octahedra control the compression of the Al2SiO5 polymorphs. The compression of the [Al1O6] octahedron in sillimanite is anisotropic with the longest Al1-OD bond shortening by ∼1.9% between room pressure and 5.29 GPa and the shortest Al1-OB bond by only 0.3%. The compression anisotropy of sillimanite is primarily a consequence of its topological anisotropy, coupled with the compression anisotropy of the Al-O bonds within the [Al1O6] octahedron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050084
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  • 4
    Electronic Resource
    Electronic Resource
    Comparative compressibility of end-member feldspars (1988)
    Springer
    Physics and chemistry of minerals 15 (1988), S. 313-318 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The compressibilities of the three end-member feldspars have been determined between 1 bar and 50 kbar by single crystal X-ray diffraction techniques, using a Merrill-Bassett type diamond anvil cell with three crystals loaded simultaneously. Low albite (ordered aluminium-silicon distribution) and high sanidine (disordered Al-Si) show similar behaviour on compression, with bulk moduli (linear fit to volume-pressure data) of 0.70 and 0.67 Mbar respectively. The most compressible cell axis of all three feldspars studied is a, indicating that the major change in the feldspar framework with pressure is a shortening of the overall length of the “crankshaft chains” by reduction of T-O-T angles. Anorthite shows anomalous behaviour in that we have observed a previously unreported reversible phase transition at a pressure between 25.5 and 29.5 kbar. This transition is marked by large discontinuities in the unit cell angles and a small decrease of 0.2 percent in the cell volume with increasing pressure. The high-pressure phase is less compressible than the low-pressure phase, the bulk moduli being 0.94 and 1.06 Mbar respectively. There was no evidence of a monoclinic to triclinic inversion in sanidine that was expected to occur between 20 and 30 kbar on the basis of previous work on intermediate alkali feldspars.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00311034
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  • 5
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    Comparative compressibility of end-member feldspars (1988)
    Springer
    Details
    Publication Date: 1988-03-01
    Print ISSN: 0342-1791
    Electronic ISSN: 1432-2021
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Springer
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  • 6
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    Compressibility and crystal structure of sillimanite, Al 2 SiO 5 , at high pressure (1997)
    Springer
    Details
    Publication Date: 1997-11-24
    Print ISSN: 0342-1791
    Electronic ISSN: 1432-2021
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Springer
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