| Reference Type | Journal (article/letter/editorial) |
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| Title | A high-pressure structural study of lawsonite using angle-dispersive powder-diffraction methods with synchrotron radiation |
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| Journal | Mineralogical Magazine |
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| Authors | Pawley, A. R. | Author |
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| Allan, D. R. | Author |
| Year | 2001 (February) | Volume | 65 |
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| Issue | 1 |
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| Publisher | Mineralogical Society |
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| DOI | doi:10.1180/002646101550118Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 243249 | Long-form Identifier | mindat:1:5:243249:0 |
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| GUID | 0 |
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| Full Reference | Pawley, A. R., Allan, D. R. (2001) A high-pressure structural study of lawsonite using angle-dispersive powder-diffraction methods with synchrotron radiation. Mineralogical Magazine, 65 (1) 41-58 doi:10.1180/002646101550118 |
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| Plain Text | Pawley, A. R., Allan, D. R. (2001) A high-pressure structural study of lawsonite using angle-dispersive powder-diffraction methods with synchrotron radiation. Mineralogical Magazine, 65 (1) 41-58 doi:10.1180/002646101550118 |
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| Abstract/Notes | AbstractStructural 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 βmono. 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. |
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