Abstract
The crystal structure of ancylite (La,Ce)1.38(Sr,Ca)0.62(CO3)2(OH)1.38·0.62H2O, a = 5.03, a = 8.53, c = 7.29 Å, space group Pmcn, Z = 2, has been determined by Patterson and Fourier methods, using 502 intensities measured with an automatic diffractometer. The least squares refinement led to a final discrepancy index R = 0.059.
The crystal structure of ancylite can be ideally derived from that of the orthorhombic carbonates with the introduction of hydroxyl groups lying on the mirror planes and bonded to the heavy cations. These have a ten-fold coordination (average M-O distance 2.61Å). The relationships between the aragonite-ancylite series and the vaterite-bastnaesite series are discussed.
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