High-pressure crystal chemistry of phenakite (Be2SiO4) and bertrandite (Be4Si2O7(OH)2)
- 80 Downloads
Compressibilities and high-pressure crystal structures have been determined by X-ray methods at several pressures for phenakite and bertrandite. Phenakite (hexagonal, space group R\(\bar 3\)) has nearly isotropic compressibility with β=1.60±0.03×10−4 kbar−1 and β=1.45±0.07×10−4 kbar−1. The bulk modulus and its pressure derivative, based on a second-order Birch-Murnaghan equation of state, are 2.01±0.08 Mbar and 2±4, respectively. Bertrandite (orthorhombic, space group Cmc21) has anisotropic compression, with β a =3.61±0.08, β b =5.78±0.13 and β c =3.19±0.01 (all ×10−4 kbar−1). The bulk modulus and its pressure derivative are calculated to be 0.70±0.03 Mbar and 5.3±1.5, respectively.
Both minerals are composed of frameworks of beryllium and silicon tetrahedra, all of which have tetrahedral bulk moduli of approximately 2 Mbar. The significant differences in linear compressibilities of the two structures are a consequence of different degrees of T-O-T bending.
KeywordsSilicon Crystal Structure Hexagonal Compressibility Mineral Resource
Unable to display preview. Download preview PDF.
- Barton MD (1986) Phase equilibria and thermodynamic properties of minerals in the BeO-Al2O3-SiO2-H2O (BASH) system, with petrologic applications. Am Mineral 71:in pressGoogle Scholar
- Downs JW (1983) An experimental examination of the electron distribution in bromellite, BeO, and phenacite, Be2SIO4. PhD Thesis, Virginia Polytechnic Institute and State University, Blacksburg, VirginiaGoogle Scholar
- Hamilton WC (1974) Angle settings for four-circle diffractometers. In: International Tables for X-ray Crystallography, Vol 4. Kynoch Press, Birmingham, England, pp 273–284Google Scholar
- Hazen RM (1985) Comparative crystal chemistry and the polyhedral approach. Rev Mineral 14:317–346Google Scholar
- Hazen RM, Finger LW (1979) Bulk modulus-volume relationship for cation-anion polyhedra. J Geophys Res 84:6723–6728Google Scholar
- Hazen RM, Finger LW (1982) Comparative Crystal Chemistry. Wiley, New YorkGoogle Scholar
- Hazen RM, Finger LW (1985) Crystals at high pressure. Sci Am 252:110–117Google Scholar
- Jorgensen JD (1978) Compression mechanisms in α-quartz structures — SiO2 and GeO2. J Appl Phys 49:5473–5478Google Scholar
- King HE, Finger LW (1979) Diffracted beam crystal centering and its application to high-pressure crystallography. J Appl Crystallogr 12:374–378Google Scholar
- Lehmann MS, Larsen FK (1974) A method for location of the peaks in step-scan-measured Bragg reflections. Acta Crystallogr A30:580–584Google Scholar
- Levien L, Prewitt CT (1981) High-pressure crystal structure and compressibility of coesite. Am Mineral 66:324–333Google Scholar
- Levien L, Prewitt CT, Weidner DJ (1980) Structure and elastic properties of quartz at pressure. Am Mineral 65:920–930Google Scholar
- Robinson K, Gibbs GV, Ribbe PH (1971) Quadratic elongation: a quantitative measure of distortion in coordination polyhedra. Science 172:567–570Google Scholar
- Simonov MA, Belov NV (1976) Crystal structures of bertrandite Be4[Si2O7](OH)2 and hemimorphite (calamine) Zn4[Si2O7](OH)2H2O. Sov Phys Dolk 21:607–608Google Scholar
- Solov'eva LP, Belov NV (1965) Precise determination of the crystal structure of bertrandite Be4[Si2O7](OH)2. Sov Phys Crystallogr 9:458–460Google Scholar
- Zachariasen WH (1967) A general theory of X-ray diffraction in crystals. Acta Crystallogr 23:558–564Google Scholar
- Zachariasen WH (1972) Refined crystal structure of phenacite Be2SiO4. Sov Phys Crystallogr 16:1021–1025Google Scholar