Synthesis and Characterization of Lansfordite and Nesquehonite

Abstract

Chemically pure lansfordite (MgCO₃·5H₂O) and nesquehonite (MgCO₃·3H₂O) were synthesized from CO₂‐saturated Mg(HCO₃)₂ solutions by degasation with air for varying periods of time depending upon equilibration temperature. Crystalline and chemical properties of the synthesized minerals were determined and the results were compared with the properties reported for geologic specimen minerals. Crystalline data determined for synthesized lansfordite are: monoclinic; a = 1.249 nm, b = 0.762 nm, c = 0.743 nm, β = 1.785 ± 0.002 rad, a/b/c = 1.638:1:0.976, Z = 4. Nesquehonite is monoclinic (pseudo‐orthorhombic); a = 1.199 nm, b = 0.769 nm, c = 0.537 nm, β = 1.573 ± 0.012 rad, a/b/c = 1.557:1:0.697, Z = 4. Lansfordite is unstable when exposed to the atmosphere at temperatures > 10°C. Large lansfordite crystals (>150 µm) were observed with scanning electron microscopy (SEM) to undergo dehydration above 10°C. X‐ray diffraction data and SEM observations indicate that upon dehydration large lansfordite crystals convert to nesquehonite but remain pseudomorphic after lansfordite. Small lansfordite crystals (<20 µm) appeared to dissolve upon an increase in temperature above 10°C when viewed with SEM. Crystal forms of nesquehonite, lansfordite, and dehydration states of lansfordite are shown in SEM microphotographs.