Low temperature synthesis and characterization of nesquehonite

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Nesquehonite, Mg(HCO3)(OH).2H2O or MgCO3.3H2O, was named after its type locality in Nesquehoning, Pennsylvania, USA. The structure of nesquehonite can be envisaged as infinite chains of corner sharing MgO6 octahedra along the b-axis. Within these chains CO32- groups link 3 MgO6 octahedra by two common corners and one edge. This structural arrangement causes strong distortion of the octahedra. Chains are interconnected by hydrogen bonds only, whereby each Mg atom is coordinated to two water ligands and one free water molecule is located in between the chains [1, 2]. Under natural conditions nesquehonite can form in evaporites depending on the availability of Mg2+ ions in solution relative to other cations, such as Ca2+ [3-5]. Additionally, nesquehonite occurs as an alteration product in the form of scales or efflorescences on existing carbonate rocks, serpentine, or volcanic breccias [6-11]. Interestingly it has also been observed on the surface of a limited number of meteorites found in Antarctic regions, where it has formed by reactions of the meteorite minerals with terrestrial water and CO2 at near freezing temperatures [12-16]. Nesquehonite has also been identified on the surfaces of manmade materials, such as bricks and mortar [17, 18]. The synthesis of nesquehonite forms a continuation of our work on the synthesis and study of the vibrational spectroscopy of natural and synthetic minerals in the hydroxide (brucite, gibbsite, boehmite, etc.)[19-23], carbonate (cerussite, azurite, malachite, etc.)[24-26] and hydroxycarbonate (hydrotalcite)[21, 27-32] groups. This work aims at describing a simple method for the synthesis of nesquehonite and the detailed characterization of the structure and morphology by X-ray diffraction (XRD), vibrational spectroscopy and scanning electron microscopy (SEM).