Synthetic quartz crystals are grown by the hydrothermal method, using an autoclave, as shown in the diagram below.
The raw material — small fragments of natural quartz crystal called “lasca“ — is placed in the bottom of the autoclave and a seed crystal is suspended at the top. The autoclave is filled with alkaline aqueous solution, sealed and brought to high temperature and pressure (approximately 350°C and 90-145 Mpa). At high temperature and pressure, the lasca at the bottom of the autoclave dissolves and the solution becomes saturated. Reducing the temperature at the top of the autoclave relative to the temperature at the bottom creates a convection current within the autoclave and the saturated solution is carried by the current towards the cooler upper part of the autoclave. The solution in the upper part of the autoclave becomes super-saturated and crystals begin to reform and grow on the surface of the seed crystal.
Synthetic quartz crystals grow at a speed of 0.4-0.5 mm per day, and take from around 40 days to as long as 200 days or more to reach full size.
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