| crystal growth in the presence of water, elevated temperatures and elevated pressures by a crystal growth process believed to proceed geologically within the Earth's crust
Note 1 to entry: The industrial synthetic quartz crystal growth processes utilize alkaline water solutions confined within autoclaves at a supercritical state with temperatures of 330 °C to 400 °C and pressures of 71 MPa to 203 MPa.
Note 2 to entry: The autoclave is divided into two chambers: the dissolving chamber, containing raw quartz chips at the higher temperature; the growing chamber, containing cut seeds at the lower temperature.
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