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Chapter 16 Notes.docx

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Earth Sciences
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Jianping Xu

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Chapter 16 Notes  Because of the large price differential that exists between natural gems and their synthetic counterparts, it is important that the gemmologist is not only able to identify a stone but is also able to determine whether it is a natural or a synthetic material  Gemstone stimulants can in general be readily identified as their physical constants differ from those of the gemstone they imitate  Synthetic versions of diamond, ruby, sapphire, emerald, quartz, and alexandrite pose a difficult problem, as their constants are very close to those of the natural stone  Other identification procedures are taken for these stones including, growth lines, colour zoning, and features called inclusions, all of which can be used to help separate the natural from the synthetic gemstone Growth Lines and Colour Zoning  Curved lines of growth and curved colour zoning are commonly seen only in coloured synthetic Verneuil corundums and in Verneuil-produced red spinel  They are due to the intermittent fall of droplets of molten alumina onto the boule’s upper surface, and to the greater volatility of some of the colouring oxides compared to alumina  Growth lines are quite difficult to detect in all but the Verneuil ruby, but curved colour zones which are often broad enough to be seen with the naked eye (particularly when the stone is immersed) are easily detected in blue Verneuil sapphires and red Verneuil spinels  As an indicator of natural origin, straight colour zoning (usually following the pattern of the lateral crystal axes) can be seen in many natural stones, including quartz,
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