Small chips of pure but un-faced quartz (1 to 1.5 inch in size), called "lascas or nutrient", are placed in a wire mesh basket and lowered into the bottom half of the vessel. A steel plate with prearranged holes, called a "baffle", is set on top of the basket. The baffle is used to separate the growth (seed) region and the nutrient region, and to help establish a temperature differential between the two regions. Suitably oriented single crystal plates (either natural or cultured), called "seed", are mounted on a rack and suspended on top of the baffle in the upper half of the vessel. The autoclave is then filled with an aqueous alkaline solution (Sodium Carbonate or Sodium Hydroxide) to approximately 80% of its free volume to allow for future liquid expansion, and it is sealed with a high-pressure closure. The autoclave is then brought to operating temperature by a series of resistive heaters attached to the exterior circumference of the cylinder. As the temperature increases, the pressure begins to build within the autoclave. A temperature of 700 to 800° F is attained in the lower half of the vessel while the top half is maintained at 70 to 80° F cooler than the bottom half.

      At operating pressure and temperature, the lascas dissolves in the heated solution in the lower half of the vessel, which then rises. As it reaches the cooler temperature of the upper part of the vessel, the solution becomes supersaturated, causing the dissolved quartz within the lascas to re-crystallize onto the seed. The cooled spent solution then returns to the lower half of the vessel to repeat the cycle until the lascas is depleted and the cultured quartz stones have reached the desired size. This so-called "Hydrothermal Process" time ranges from 25 to 365 days, depending upon the desired stone size, properties, and the process type – Sodium Hydroxide or Sodium Carbonate.

3. Symmetry, Twinning and Size of Quartz Crystal

        Alpha-quartz belongs to the crystallographic class 32, and it is a hexagonal prism with six cap faces at each end. The prism faces are designated m-faces and the cap faces are designated R and r-faces. The R-faces are often called major rhomb faces and the r-faces are minor rhomb faces.  Both left-hand and right-hand crystals occur naturally and can be distinguished by the position of the S and X faces.

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