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Unit-cell parameters for scapolite solid solutions and a discontinuity at Me 75, ideally NaCa3[Al5Si7O24](CO3)
Published online by Cambridge University Press: 04 September 2013
Abstract
Twenty-seven scapolite samples from various localities and with compositions between Me 6–93 were obtained using electron microprobe analysis (EMPA). Their unit-cell parameters were obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements using space group P42/n. The EMPA data show the well-known discontinuity at Me 75. In addition, the unit-cell parameters, especially c, show a discontinuity at Me 75 (=five Al atoms per formula unit, apfu), ideally NaCa3[Al5Si7O24](CO3), where the scapolite solid solution is divided into two (Me% = [Ca/(Ca + Na + K)] × 100). A maximum c parameter value occurs at Me 37.5 (=four Al apfu ideally), where complete Al–Si, Na–Ca, and Cl–CO3 order occurs. The unit-cell volume, V, varies smoothly with Me% and Al apfu across the series.
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- Copyright © International Centre for Diffraction Data 2013
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