A SYNTHETIC gemstone is not merely an imitation which resembles, at least to some extent, a natural gemstone. To deserve fully the destination “SYNTHETIC” a man-made gemstone needs to have the same appearance, the same chemical composition and crystal structure, which will, of course, produce the same hardness, optical properties, and so on, as the natural gem.
In the earliest recorded attempts to synthesize gems, natural stones were buried in the ground in the hope that they would reproduce or grow larger. Later, chemists attempted to imitate the process of nature, and throughout the nineteenth century scientists experimented with crystal growth.
There are three major methods used today to make synthetic gem minerals commercially.
1] Flame fusion method:
In this method (a type of MELT GROWTH), powdered oxides are melted in a furnace and crystallization takes place. By this technique, corundum and a number of other gem materials are made, including rutile, strontium titanate and spinel, as well as non-gem minerals like cadmium tungstate and synthetic scheelite. A modification of the melt-growth technique known as the CZOCHRALSKI method produces high quality crystals for use in industry as well as in jewellery. In this technique a rod is pulled slowly from a melt; as the material leaves the melt, it crystallizes on the end of the rod. The Skull Melt method is another modification of melt-growth used to produce Cubic Zirconia.
2] Flux growth method:
In this method, materials are dissolved at high temperatures and pressures, in a molten flux in which they are more readily soluble than in water. (Flux is a general term for a number of different materials, for example lithium molybdate – Li2, MO2, O7 and Lithium Vanadate – LiVO3, which are high temperature solvents). Chatham and Gilson synthetic Emeralds and Chatham and Kashan synthetic Rubies are made by this method. (Synthetic Alexandrite can be flux grown or produced by the Czochralski method).
3] Hydrothermal method:
The refix “hydro” means having to do with water and “thermal” means having to do with heat. This process involves growing crystals at high temperatures and pressures in a water solution. Most of the important types of gem minerals have been produced by crystallization from solution (hydrothermal methods) in laboratory experiments, however quartz and beryl (emerald) are produced on a commercial scale.
There are other methods that can be used at least experimentally for mineral synthesis. One is the formation of minerals by direct passage from vapor to a solid state (without first passing through the liquid state) called VAPOR GROWTH or DEPOSITION.Some early experiments in diamond synthesis claimed to have produced tiny diamond crystals by the solidification of carbon from a gaseous state. This was never proved, but Dupont now makes tiny industrial diamonds by exploding charges in strong walled sealed containers filled with gaseous carbon. The structure of these diamonds makes them very useful for industrial grinding.