The structure of braitschite, a calcium rare earth borate

作者：Rowland Clare E^*; Cahill Christopher L; Post Jeffrey E

来源：American Mineralogist, 2011, 96(1): 197-201.

DOI：10.2138/am.2011.3592

• Braitschite
• borate
• rare earth mineral
• crystal structure

The crystal structure of braitschite, Ca6.15Na0.85RE2.08[B6O7(OH)(3)(O,OH)(3)](4)(H2O), is reported here in space group P6/m with unit-cell parameters a = 12.1506(6), c = 7.3678(4) angstrom, and V= 942.03(8) angstrom(3). Data were collected from a single crystal using a MoK alpha source and a CCD detector, solved by direct methods, and refined to an R factor of 2.81%. The mineral structure consists of hexaborate fundamental building blocks that polymerize along [001] and are bound by Ca2+ and REE3+ counterions. The framework forms hexagonal channels, which are occupied alternately by Ca2+ cations and water molecules. In an investigation or its thermal stability, braitschite maintains its crystallinity to a temperature of 400 degrees C, after which it undergoes decomposition. Using Rietveld refinements against powder X-ray diffraction data, we were able to track the loss of water molecules in channels and hydroxyl groups in the covalent B-O network with increasing temperature.

• 出版日期2011-1