Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Pawley, A. R. Articles by Allan, D. R. Search for Related Content GeoRef GeoRef Citation

A high-pressure structural study of lawsonite using angle-dispersive powder-diffraction methods with synchrotron radiation

¹ Department of Earth Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK
² Department of Physics and Astronomy, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, UK

^* E-mail: alison.pawley{at}man.ac.uk

Structural refinements of lawsonite have been obtained at pressures up to 16.5 GPa using angle-dispersive powder diffraction with synchrotron radiation on a natural sample contained in a diamond anvil cell. Lawsonite compresses smoothly and relatively isotropically up to 10 GPa. Its bulk modulus is 126.1(6) GPa (for K'= 4), consistent with previous results. A trend of decreasing Si–O–Si angle indicates that compression is accommodated partly through the narrowing of the cavities containing Ca and H₂O in the [001]ortho direction. At 10–11 GPa there is a phase transition from Cmcm to P2₁/m symmetry. The occurrence of a mixed-phase region, spanning >1 GPa, indicates that the transition is first order in character. The phase transition occurs through a shearing of (010)_ortho sheets containing AlO₆ octahedral chains in the [100]_ortho direction, which causes an increase in ß_mono. Across the transition, the number of oxygens coordinated to Ca increases from 8 to 9, causing an increase in the average Ca–O bond length. The compressibility of P2₁/m lawsonite could not be determined due to solidification of the methanol/ethanol pressure-transmitting medium. On the basis of an experiment in which the P2₁/m lawsonite structure was heated to 200°C at 12.0 GPa, we predict a shallow positive P-T slope for the phase transition, and therefore no stability field for P2₁/m lawsonite in the Earth.

KEYWORDS: lawsonite, high-pressure, phase transition, synchrotron radiation, powder diffraction

This article has been cited by other articles:

				H. P. Scott, Z. Liu, R. J. Hemley, and Q. Williams High-pressure infrared spectra of talc and lawsonite American Mineralogist, November 1, 2007; 92(11-12): 1814 - 1820. [Abstract] [Full Text] [PDF]

				G. Dorsam, A. Liebscher, B. Wunder, G. Franz, and M. Gottschalk Crystal chemistry of synthetic Ca2Al3Si3O12OH-Sr2Al3Si3O12OH solid-solution series of zoisite and clinozoisite American Mineralogist, July 1, 2007; 92(7): 1133 - 1147. [Abstract] [Full Text] [PDF]

				M. A. Carpenter Elastic properties of minerals and the influence of phase transitions American Mineralogist, February 1, 2006; 91(2-3): 229 - 246. [Abstract] [Full Text] [PDF]

				Z. Liu, Z. Liu, G. A. Lager, R. J. Hemley, and N. L. Ross Synchrotron infrared spectroscopy of OH-chondrodite and OH-clinohumite at high pressure American Mineralogist, October 1, 2003; 88(10): 1412 - 1415. [Abstract] [Full Text] [PDF]

				M. A. Carpenter, M. A. Carpenter, H.-W. Meyer, P. Sondergeld, S. Marion, and K. S. Knight Spontaneous strain variations through the low temperature phase transitions of deuterated lawsonite American Mineralogist, April 1, 2003; 88(4): 534 - 546. [Abstract] [Full Text] [PDF]

				T. B. BALLARAN and R. J. ANGEL Equation of state and high-pressure phase transitions in lawsonite European Journal of Mineralogy, April 1, 2003; 15(2): 241 - 246. [Abstract] [Full Text] [PDF]