Characterises a suite of 40 natural brown to black diamonds from this deposit so that they can be distinguished from suspected treated black diamonds.
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Describes the occurrence of iridescence, and the role of differential etching, in quartz crystals from India’s Jalgaon District.
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Examines a collection of chrysoberyl samples from these sapphire placer deposits to determine their distinct mineralogical and chemical properties.
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An introduction to Moroccan amethyst, which features distinctive color zoning and inclusions.
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Describes the phenomenon of pleochroism and its complex effect on the appearance of coloured stones.
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How contrast patterns can increase perceived brightness and optimise a gemstone's appearance.
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How variations in UV lamp output can affect observed fluorescence colour and intensity.
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A simple chart of optical defects in diamond, including those that produce colouration and fluorescence colours.
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Knowledge of type allows gemmologists to better evaluate if a diamond might be treated or synthetic, and whether it should be sent to a laboratory for testing.
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This article reviews the GIA Laboratory’s history of reporting on certain types of graining which are often the only characteristics present in large, high-clarity, high-colour diamonds.
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