Crystal structure of nesquehonite, MgCO3·3H(D)2O by neutron diffraction and effect of pH on structural formulas of nesquehonite

• Published in: Journal of Mineralogical and Petrological Sciences Vol. 116; no. 2; pp. 96 - 103
• Main Authors: YAMAMOTO, Gen–ichiro, KYONO, Atsushi, ABE, Jun, SANO–FURUKAWA, Asami, HATTORI, Takanori
• Format: Journal Article
• Language: English
• Published: Sendai Japan Association of Mineralogical Sciences 2021; Japan Science and Technology Agency
• Subjects: Analytical methods; Carbonates; Crystal lattices; Crystal structure; Deuteration; Deuterium; Diffraction; Diffraction patterns; Hydrates; Hydrogen–bonding network; Lattice parameters; Magnesium; Magnesium carbonate; Magnesium carbonate hydrate; Molecular structure; Nesquehonite; Neutron diffraction; Neutrons; Raman spectroscopy; Thermal analysis; Water chemistry
• ISSN: 1345-6296; 1349-3825
• DOI: 10.2465/jmps.200117

Neutron diffraction, Raman spectroscopy, and thermal analysis were performed to investigate the composition, structure, and formation conditions of the magnesium carbonate hydrate nesquehonite. The crystal structure of deuterated nesquehonite was analyzed by Rietveld refinement of the time–of–flight neutron powder diffraction pattern. The crystal structure possessed the monoclinic space group P21/n with lattice parameters of a = 7.72100(12) Å, b = 5.37518(7) Å, c = 12.1430(3) Å, β = 90.165(4)°, and V = 503.956(13) Å3. The refinement with a final crystal structure model of deuterated nesquehonite converged to wRp = 4.22% and Rp = 3.50%. The result of structure refinement showed that two deuterium atoms are coordinated to the O1, O2, and O6 atoms as a water molecule in the nesquehonite. The fact that the three water molecules were included in the structure suggests the structural formula of the nesquehonite obtained in the study should be written as MgCO3·3H2O not Mg(HCO3)(OH)·2H2O.