The crystal structure of cyanotrichite, having general formula Cu<inf>4</inf>Al<inf>2</inf>(SO<inf>4</inf>)(OH)<inf>12</inf>·2H<inf>2</inf>O, from the Dachang deposit (China) was studied by means of conventional transmission electron microscopy, automated electron diffraction tomography (ADT) and synchrotron X-ray powder diffraction (XRPD). ADT revealed the presence of two different cyanotrichite-like phases. The same phases were also recognized in the XRPD pattern, allowing the perfect indexing of all peaks leading, after refinement to the following cell parameters: (1) a = 12.417(2) Å, b = 2.907(1) Å, c = 10.157(1) Å and β = 98.12(1); (2) a = 12.660(2) Å, b = 2.897(1) Å, c = 10.162(1) Å and β = 92.42(1)°. Only for the former phase, labeled cyanotrichite-98, a partial structure, corresponding to the [Cu<inf>4</inf>Al<inf>2</inf>(OH)<inf>12</inf> <sup>2+</sup>] cluster, was obtained ab initio by direct methods in space group C2/m on the basis of electron diffraction data. Geometric and charge-balance considerations allowed to reach the whole structure model for the cyanotrichite-98 phase. The sulfate group and water molecule result to be statistically disordered over two possible positions, but keeping the average structure consistent with the C-centering symmetry, in agreement with ADT results.
Ventruti, G., Mugnaioli, E., Capitani, G., Scordari, F., Pinto, D., Lausi, A. (2015). A structural study of cyanotrichite from Dachang by conventional and automated electron diffraction. PHYSICS AND CHEMISTRY OF MINERALS, 42(8), 651-661 [10.1007/s00269-015-0751-z].
A structural study of cyanotrichite from Dachang by conventional and automated electron diffraction
AbstractThe crystal structure of cyanotrichite, having general formula Cu
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