Unit-cell parameters for scapolite solid solutions and a discontinuity at Me-75, ideally NaCa3[Al5Si7O24](CO3)

作者：Antao Sytle M^*

来源：Powder Diffraction, 2013, 28(4): 269-275.

DOI：10.1017/S0885715613000638

• Scapolite
• solid solutions
• unit-cell parameters
• HRPXRD
• end-member Me-75
• Rietveld refinement
• crystal structure

Twenty-seven scapolite samples from various localities and with compositions between Me6-93 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 P4(2)/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)] x 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.

• 出版日期2013-12