Abstract: A process for producing amethyst crystals involving growing of colorless quartz crystals by a hydrothermal method of a temperature drop in a high-pressure autoclave on crystalline quartz seed plates oriented parallel to the crystallographic planes of the major {1011} and minor {1101} rhombohedrons using crystalline quartz as a charge. Said growing is effected from aqueous solutions of potassium carbonate or potassium hydroxide having a concentration ranging from 4 to 7 wt.% and containing iron introduced into the autoclave in the form of metallic iron or in the form of its oxydic or hydroxydic compounds in an amount ranging from 5 to 30 g/l of the solution. The growing process is effected at a crystallization temperature within the range of from 300.degree. to 500.degree. C. under a pressure ranging from 200 to 1,700 kg/cm.sup.2 and a crystal growth rate of from 0.05 to 0.5 mm/day.

Abstract: An apparatus for growing crystals from hydrothermal solutions comprises a vertically extending autoclave having a crystallization zone in its top portion and a dissolution zone in its bottom portion. The autoclave is surrounded by a heat insulation layer, is provided with a system of heating elements and is enclosed in a thermostatically controlled chamber which is divided into vertically extending sections. Each section is provided with a heating and thermostatic control system so as to ensure the maintenance of constant and different temperature values in each section required to create and maintain the desired temperature fields in the crystallization and dissolution zones of the autoclave.