The crystal structure of coesite, the dense, high-pressure form of silica

Zoltai, Tibor; Buerger, Μ. J.

doi:10.1524/zkri.1959.111.1-6.129

Cited by 73 publications

(20 citation statements)

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“…It is approximately equi-dimensional ( ---0.2 mm in diameter) without plane faces. Precession photographs are consistent with the space group C 2jc previously determined by ZOLTAI and BUERGER (1959) and ARAKI and ZOLTAI (1969). The cell parameters refined by least squares using 19 single-crystal reflections are given in Table 1 along with those determined by ARAKI and ZOLTAI.…”

Section: Methodssupporting

confidence: 64%

A study of the structural chemistry of coesite

Gibbs¹

1977

Zeitschrift Für Kristallographie - Crystalline Materials

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AuszugIn order to obtain the best possible set of Si-O distances, we refined the structure using single-crystal diffraction data from a synthetic crystal (unweighted R = 0.024). Cell parameters for this crystal are a = 7.135(1) A, b = 12.372(1), C = 7.173(1), and f3 = 120.36(1).A Mulliken population analysis was calculated with all Si-0 bond lengths clamped at 1.614 A and using the valence angles determined by ARAKI and ZOLTAI (1969) for which R = 0.076, and those obtained from the present experiment., The Si-0 bond overlap populations calculated using the valence angles ()btained for the new coordinates were found to be more highly correlated

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Section: Methodssupporting

confidence: 64%

A study of the structural chemistry of coesite

Gibbs¹

1977

Zeitschrift Für Kristallographie - Crystalline Materials

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“…If Si occupied the T-site, alternatively, its Raman signals would resemble those of Fo because Si in Fo also adopts an isolated T-site and forms a separate SiO 4 group, with the oxygen atoms being shared between neighboring octahedral [94]. On the other hand, Si atoms in low Qz [95] and Coe [96] are 4-coordinated, but the SiO 4 tetrahedra are fully polymerized into a three-dimensional framework, so that the Raman features of low Qz and Coe should be very different to those of potential SiO 4 groups in the Sp structure.…”

Section: Raman Features Of Si-bearing Fully Disordered Mgal 2 O 4 -Spmentioning

confidence: 99%

Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite

Liu

Bao

et al. 2018

Minerals

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A series of Si-bearing MgAl 2 O 4 -spinels were synthesized at 1500-1650 • C and 3-6 GPa. These spinels had SiO 2 contents of up to~1.03 wt % and showed a substitution mechanism of Si 4+ + Mg 2+ = 2Al 3+ . Unpolarized Raman spectra were collected from polished single grains, and displayed a set of well-defined Raman peaks at~610, 823, 856 and 968 cm −1 that had not been observed before. Aided by the Raman features of natural Si-free MgAl 2 O 4 -spinel, synthetic Si-free MgAl 2 O 4 -spinel, natural low quartz, synthetic coesite, synthetic stishovite and synthetic forsterite, we infer that these Raman peaks should belong to the SiO 4 groups. The relations between the Raman intensities and SiO 2 contents of the Si-bearing MgAl 2 O 4 -spinels suggest that under some P-T conditions, some Si must adopt the M-site. Unlike the SiO 4 groups with very intense Raman signals, the SiO 6 groups are largely Raman-inactive. We further found that the Si cations primarily appear on the T-site at P-T conditions ≤~3-4 GPa and 1500 • C, but attain a random distribution between the T-site and M-site at P-T conditions ≥~5-6 GPa and 1630-1650 • C. This Si-disordering process observed for the Si-bearing MgAl 2 O 4 -spinels suggests that similar Si-disordering might happen to the (Mg,Fe) 2 SiO 4 -spinels (ringwoodite), the major phase in the lower part of the mantle transition zone of the Earth and the benchmark mineral for the very strong shock stage experienced by extraterrestrial materials. The likely consequences have been explored.

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“…In contrast, the structures of many framework compounds have been described in terms of subunits, for example analcime in terms of four-and six-membered rings of tetrahedra (Taylor, 1930), and coesite in terms of four-membered rings (Zoltai and Buerger, 1959). Other structures have been described in terms of 'infinite' planar or linear units, for example feldspar in terms of the 'crankshaft chain' (Taylor, 1933), and tridymite in terms of planes of tetrahedra (Konnert and Appleman, 1978).…”

Section: T~ Copyright the Mineralogical Societymentioning

confidence: 99%

The Structural behaviour of tetrahedral framework compounds—a review. Part I. Structural behaviour

Taylor

1983

Mineral. mag.

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ABSTRACT. Tetrahedral framework compounds, as defined in this paper, generally exist as tilted and distorted versions of ideal fully expanded structures at room temperature and atmospheric pressure. How pressure, temperature, and composition (P, T, and X) affect the tilting and distortion is critically reviewed. Although P, T, and X are generally regarded as analogous variables in their effect on framework structures there is reason to believe that they have different structural effects. In particular, an important, and frequently neglected, thermal effect is the apparent shortening of the framework bonds by the anisotropic thermal motion of the framework oxygens. The effects of P, T, and X on displacive transformations in framework compounds are reviewed with particular reference to the disordered alkali feldspars and the leucites. It seems probable from the available evidence that displacive transformations do not take place at a critical size of the framework. Displacive transformations can take place with or without a volume discontinuity and hysteresis. Furthermore, the effects of P, T, and X on a solid-solution series with a displacive transformation can be different, one variable causing a volume discontinuity and another a smooth transition.

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The crystal structure of coesite, the dense, high-pressure form of silica

Cited by 73 publications

References 0 publications

A study of the structural chemistry of coesite

A study of the structural chemistry of coesite

Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite

The Structural behaviour of tetrahedral framework compounds—a review. Part I. Structural behaviour

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