By controlling the growth conditions, especially time and nucleation density, it is possible to grow much higher quality stones with well-defined crystal forms: cubic at low temperature, cubo — octahedra at intermediate temperatures, and octahedra at the highest temperatures. The diagram for growth morphologies of diamond is shown in Figure 5.9.
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The characteristic shape of good-quality natural stones is octahedral, but the toughest stone shape is cubo-octahedral. Unlike in nature, this can be grown consistently by manipulation of the synthesis process. This has led to a range of synthetic diamond grades typified by the MBG series from GE and the PremaDia series from De Beers [1999], which are the abrasives of choice for saws used in the stone and construction industry and for glass grinding wheels.
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