The crystal structure of zircon is tetragonal ..
Analysis of silica fume produced by zircon ..
There are three major methods used today to make synthetic gem minerals commercially. In the first, the flame-fusion process, powdered oxide are melted in a furnace by a high-temperature flume and accumulated in hardened form as cooling and crystallization take place. By this technique, corundum and a number of other gem minerals are made, including rutile, strontium titanate and spinel, as well as the non gem minerals cadmium tungstate and calcium tungstate (synthetic scheelite). By the second method, a hydrothermal process, quartz, opal, beryl (emerald) corundum and fluorite are crystallized from solution under conditions of high temperature and pressure, by dissolving fragments of the mineral and re-depositing it as transparent, gem-quality crystals. In laboratory experiments, most of the important gem minerals have been produced by crystallization from solution (hydrothermal methods); however, only those mentioned above are produced on a commercial scale. The third method is termed flux growth, and this is a means by which under high temperature and pressure conditions, materials are dissolved in a melt in which they are more readily soluble than in water. A modification of the melt-growth technique is the Czochralski or crystal-pulling technique. It is by this method that Chatham and Gilson have made their synthetic emeralds, and it is also the method by which Chatham and Kashan are making synthetic rubies. Synthetic alexandrites and sapphires are also flux grown.
Crystal Color Wheel and Elements of Color
Metal sulfides are of interest for a wide variety of applications, including use as hydrodesulfurization catalysis, and as photovoltaic materials. Many transition metal sulfides have complex structures due to the combination of variable oxidationstate on the transition metal, and the fact that sulfur can exist as S2 or S3 units in addition to isolated monoatomic anions. Some of these compounds are only stable at low temperatures, converting to simpler, more thermodynamically stable phases at higher temperatures. This makes synthesis somewhat difficult.