Synthetic quartz

synthetic quartz

Not all varieties of quartz are naturally occurring. Because natural crystal is often twinned, synthetic quartz is produced for use in industry. Large, flawless, single crystals are synthesized in an autoclave via the hydrothermal process.

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Synthetic quartz includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures, also termed hydrothermal method, hydrothermal is of geologic origin. Geochemists and mineralogists have studied hydrothermal quartz equilibria since the beginning of the twentieth century.

Hydrothermal synthesis

Hydrothermal synthesis can be defined as a method of synthesis of single crystals that depends on the solubility of minerals in hot water under high pressure. The quartz crystal growth is performed in an apparatus consisting of a steel pressure vessel called an autoclave, in which a nutrient is supplied along with water.

A temperature gradient is maintained between the opposite ends of the growth chamber. At the hotter end the nutrient solute dissolves, while at the cooler end it is deposited on a seed crystal, growing the desired crystal.

Advantages of the synthetic hydrothermal quartz method

Advantages of the hydrothermal method over other types of crystal growth include the ability to create crystalline phases which are not stable at the melting point. Also, materials which have a high vapor pressure near their melting points can be grown by the hydrothermal method.

The method is also particularly suitable for the growth of large good-quality crystals quartz while maintaining control over their composition. Disadvantages of the method include the need of expensive autoclaves, and the impossibility of observing the crystal as it grows if a steel tube is used. There are autoclaves made out of thick-walled glass, which can be used up to 300°C and 10 bars.

  • MINERAL: Oxide mineral
  • COLOR: Colorless through various colors to black
  • REFRACTIVE INDEX: 1.54 to 1.55
  • SPECIFIC GRAVITY: 2.59–2.65

Synthetic quartz history

The first report of the hydrothermal growth of crystals was by German geologist Karl Emil von Schafhäutl (1803–1890) in 1845 he grew microscopic crystals in a pressure cooker.

Synthetic quartz

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