The crystal structure of nesquehonite, MgCO₃ · 3H₂O, from Lavrion, Greece

Author(s)

G. Giester, C. L. Lengauer, B. Rieck

Abstract

Nesquehonite, MgCO₃ · 3H₂O, has been observed from Sounion, Lavrion mining district, Greece as a late alteration product in crystals up to 4 mm in size. The structure was refined in P2₁/n, Z = 4, to R = 0.032 using CCD X-ray single-crystal data of a twinned specimen showing orthorhombic pseudosymmetry. The precise cell parameters a = 7.701(1) Å, b = 5.365(1) Å, c = 12.126(2) Å, β = 90.41(1)°, and V = 501.0(1) ų were obtained from a Rietveld refinement of high resolution X-ray powder data with a calculated density of 1.835 gcm^-3. The atomic coordinates of the Mg, C and O atoms are in accordance to published data, the hydrogen bond system, however, could now be established on the basis of experimentally determined H positions. 

The structure of nesquehonite is characterized by infinite chains along [010], formed by cornersharing MgO₆ octahedra. Within the chains, CO₃ groups link three MgO₆ octahedra by two common corners and one edge, which causes strong distortions of the involved polyhedra. These chains are interconnected via hydrogen bonds only: each Mg atom is coordinated by two H₂O ligands, and one free water molecule is situated between the chains. Mean bond lengths are 2.076 Å for Mg-O and 1.283 Å for C-O, the aplanarity of the carboate group is 0.025(3) Å. Of the six hydrogen bonds, five are usual ones with O-H⋯O from 2.738(2) Å to 2.820(2) Å, the sixth one is found to be bifurcated.

Organisation(s)

Department of Mineralogy and Crystallography

Journal

Mineralogy and Petrology

Volume

70

Pages

153-163

No. of pages

11

ISSN

0930-0708

Publication date

12-2000

Peer reviewed

Yes

Austrian Fields of Science 2012

105116 Mineralogy, 105113 Crystallography

ASJC Scopus subject areas

Geophysics, Geochemistry and Petrology

Portal url

https://ucrisportal.univie.ac.at/en/publications/8ad129b7-d72d-4d16-b330-20e4619a7b40