Hydrothermal growth of calcite single crystals in nitrate solutions

Calcite single crystals could be hydrothermally grown in newly discovered NH4NO3 solution even at 150°C. The solubility of calcite in NH4NO3 solution was 4.0g/l at 100°C and 30MPa, and increased with increasing temperature and pressure. The dislocation densities of grown calcite crystals on as-cleaved and etched seeds were 4×105 and 2×104cm-2, respectively. The growth rate on etched seeds was dependent upon both growth temperature and concentration of solution. The maximum growth rate was 45μm/day in 0.2M NH4NO3 solution at 200°C and 15MPa. Calcite crystals grown on etched seeds had the same order of dislocation density as that of high grade natural crystals, and were free from OH- and NO3- ions. This moderate growth condition allows us to employ a Teflon liner for avoiding the contamination from the pressure vessel to grow the optical grade of calcite single crystals.