SYNTHESIS OF LANSFORDITE MgCO_3·5H_2O AND ITS CRYSTAL STRUCTURE INVESTIGATION

摘要

Euhedral crystals of the uncommon low-temperature mineral lansfordite have been obtained by the synthetic method, and the crystal structure analysis has been accomplished correspondingly. The structural parameters and the general view of structure were presented for the first time. The results obtained show that the coordination configuration of two magnesium ions in the unit cell is octahedral arrangement and the coordination number is 6, but in two forms: one in the complex ion Mg（CO3）2（H2O）42- and the other in the Mg（H2O）62+. There is only a CO32- group in the structure, not three distinct groups as reported by Hill et al. previously based on the IR absorption spectrum research data. The authors of this paper believe that the exact chemical formula of lansfordite should be expressed as "Mg（H2O）6. Mg（CO3）2 （H2O）4", and MgCO3-5H2O is only a simple chemical expression.