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Fancy Dark brown to Fancy black Marange diamonds
Black Diamonds from Marange (Zimbabwe): A Result of Natural Irradiation and Graphite Inclusions

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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Iridescence in iris quartz from Jalgaon, India
Causes of Iridescence in Natural Quartz

Describes the occurrence of iridescence, and the role of differential etching, in quartz crystals from India’s Jalgaon District.

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Faceted blue zircons
Reversible Colour Modification of Blue Zircon by Long-Wave Ultraviolet Radiation

Determines whether blue zircon, inadvertently altered to brown by exposure to long-wave UV radiation, can be restored to its original colour through the use of incandescent light.

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chrysoberyl samples
Chrysoberyl from the New England Placer Deposits, New South Wales, Australia

Examines a collection of chrysoberyl samples from these sapphire placer deposits to determine their distinct mineralogical and chemical properties.

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Color zoning in amethyst from Boudi, Morocco
Amethyst from Boudi, Morocco

An introduction to Moroccan amethyst, which features distinctive color zoning and inclusions.

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15 ct tanzanite
Pleochroism in Faceted Gems: An Introduction

Describes the phenomenon of pleochroism and its complex effect on the appearance of coloured stones.

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Fluorescence produced by optical defects in diamond: measurement, characterisation and challenges

How variations in UV lamp output can affect observed fluorescence colour and intensity.

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Optical defects in diamond: a quick reference chart

A simple chart of optical defects in diamond, including those that produce colouration and fluorescence colours.

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Optimising Face-Up Appearance in Coloured Gemstone Faceting

How contrast patterns can increase perceived brightness and optimise a gemstone's appearance.

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Coloured Diamonds in the Aurora Butterfly of Peace Collection
The “Type” Classification System of Diamonds and Its Importance in Gemmology

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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