Thermal Alteration of Inclusions in "Rutilated" Topaz

Kammerling, Robert C.; Koivula, John I.

doi:10.5741/gems.25.3.165

Cited by 5 publications

(1 citation statement)

References 3 publications

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“…The dehydration of goethite as a marker for a gemstone heat treatment has been known in the gemmological literature for quite some time [40][41][42][43]. The focus of this study is to present detailed data of in situ heating experiments not only for the goethite-hematite phase transformation but also for the dehydration of diaspore.…”

Section: Introductionmentioning

confidence: 99%

Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires

Krzemnicki,

Lefèvre,

Zhou

et al. 2023

Minerals

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Gem-quality rubies and sapphires are often commercially heat treated at about 800 °C or higher to enhance their color and clarity, and hence quality. For this study, selected corundum samples containing diaspore and goethite inclusions were heated step-by-step to a maximum of 1000 °C with the aim of monitoring the dehydration and phase transformation of these oxyhydroxides to corundum and hematite during heating. Based on our experiments and in agreement with the literature, the dehydration of diaspore in corundum occurs between 525 and 550 °C, whereas goethite transforms to hematite between 300 and 325 °C. As both diaspore and goethite may be present as inclusions in rubies, sapphires, and other corundum varieties (e.g., pink sapphires, padparadscha), these dehydration reactions and phase transformations can be considered important criteria to separate unheated from heated stones, specifically in cases in which other methods (e.g., microscopy, FTIR) are unsuccessful.

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Section: Introductionmentioning

confidence: 99%

Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires

Krzemnicki,

Lefèvre,

Zhou

et al. 2023

Minerals

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Spectroscopic investigation and colour change of natural topaz exposed to PbO and CrO3 vapour

Rout

Sahoo

Singh

et al. 2017

Vibrational Spectroscopy

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Dehydration of Diaspore and Goethite during low-Temperature Heating as Criterion to separate Unheated from Heated Rubies and Sapphires

Krzemnicki,

Lefèvre,

Zhou

et al. 2023

Preprint

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A Gem-quality rubies and sapphires are often commercially heat treated at about 800°C or higher temperatures to enhance their colour and clarity, and hence quality. For this study, selected corundum samples containing diaspore- and goethite inclusions were heated step-by-step to a maximum of 1000 °C with the aim to monitor the dehydration and phase transformation of these oxyhydroxides to corundum and hematite during heating. Based on our experiments and in agreement with literature, the dehydration of diaspore in corundum occurs between 525 to 550 °C, whereas goethite transforms to hematite already between 300 and 325 °C. As both, diaspore and goethite are common inclusions in rubies, sapphires, and other corundum varieties, these dehydration reactions and phase transformations can be considered important criteria to separate unheated stones from heated ones, specifically in cases in which other methods (e.g. microscopy, FTIR) are unsuccessful.

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Thermal Alteration of Inclusions in "Rutilated" Topaz

Cited by 5 publications

References 3 publications

Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires

Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires

Spectroscopic investigation and colour change of natural topaz exposed to PbO and CrO3 vapour

Dehydration of Diaspore and Goethite during low-Temperature Heating as Criterion to separate Unheated from Heated Rubies and Sapphires

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