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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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1945-3027
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Volume 92, Issue 10

Issues

Acoustic dissipation associated with phase transitions in lawsonite, CaAl2Si2O7(OH)2·H2O

Ruth E.A. Mcknight
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  • Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, U.K.
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/ Michael A. Carpenter
  • Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, U.K.
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/ Tim W. Darling / Andy Buckley
  • Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, U.K.
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/ Paul A. Taylor
  • Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, U.K.
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Published Online: 2015-04-01 | DOI: https://doi.org/10.2138/am.2007.2568

Abstract

Resonant ultrasound spectra of a single crystal and a polycrystalline sample of lawsonite [CaAl2Si2O2(OH)2·H2O] have been measured at room temperature and at low temperatures in the region 20-300 K. The influence of known phase transitions at 125 and 270 K is seen in the frequency variations of the resonance peaks, which are indicative of elastic stiffening, and in values for the quality factor QQF, which are indicative of dissipation. Two dissipation peaks, at ~250 and ~210 K, are interpreted as being due to the proton order-disorder processes associated with the two species of hydrogen atoms in the structure: one in hydroxyl OH groups and one in the H2O molecules. These occur below the Cmcm ↔ Pmcn transition point but coincide with changes in the shear elastic constants and in features of IR spectra reported elsewhere. A third, much smaller, dissipation peak occurs immediately below the Pmcn ↔ P21cn transition point. The combination of these anomalies in acoustic dissipation and in elastic constants is consistent with the view that the Cmcm ↔ Pmcn transition is driven both by displacive and proton ordering effects. For the Pmcn ↔ P21cn transition, dissipation and the transition are more closely related, consistent with the view that the transition is driven essentially by proton ordering.

Keywords: Lawsonite; resonant ultrasound spectroscopy; dissipation; proton ordering

About the article

Received: 2007-01-18

Accepted: 2007-06-18

Published Online: 2015-04-01

Published in Print: 2007-10-01


Citation Information: American Mineralogist, Volume 92, Issue 10, Pages 1665–1672, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am.2007.2568.

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