Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires
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...
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| Format: | Article |
| Language: | English |
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MDPI AG
2023-12-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/13/12/1557 |
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| author | Michael S. Krzemnicki Pierre Lefèvre Wei Zhou Judith Braun Georg Spiekermann |
| author_facet | Michael S. Krzemnicki Pierre Lefèvre Wei Zhou Judith Braun Georg Spiekermann |
| author_sort | Michael S. Krzemnicki |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-03-08T20:31:26Z |
| format | Article |
| id | doaj.art-f2b70e3fa3bf46a0b34986e86e26aa0b |
| institution | Directory Open Access Journal |
| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-08T20:31:26Z |
| publishDate | 2023-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Minerals |
| spelling | doaj.art-f2b70e3fa3bf46a0b34986e86e26aa0b2023-12-22T14:26:51ZengMDPI AGMinerals2075-163X2023-12-011312155710.3390/min13121557Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and SapphiresMichael S. Krzemnicki0Pierre Lefèvre1Wei Zhou2Judith Braun3Georg Spiekermann4Swiss Gemmological Institute SSEF, Aeschengraben 26, 4051 Basel, SwitzerlandSwiss Gemmological Institute SSEF, Aeschengraben 26, 4051 Basel, SwitzerlandSwiss Gemmological Institute SSEF, Aeschengraben 26, 4051 Basel, SwitzerlandSwiss Gemmological Institute SSEF, Aeschengraben 26, 4051 Basel, SwitzerlandExperimental Mineral Physics, Institute for Geochemistry and Petrology, Federal Institute of Technology, 8092 Zurich, SwitzerlandGem-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.https://www.mdpi.com/2075-163X/13/12/1557rubysapphirelow-temperature heatingdiasporegoethiteRaman |
| spellingShingle | Michael S. Krzemnicki Pierre Lefèvre Wei Zhou Judith Braun Georg Spiekermann Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires Minerals ruby sapphire low-temperature heating diaspore goethite Raman |
| title | Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires |
| title_full | Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires |
| title_fullStr | Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires |
| title_full_unstemmed | Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires |
| title_short | Dehydration of Diaspore and Goethite during Low-Temperature Heating as Criterion to Separate Unheated from Heated Rubies and Sapphires |
| title_sort | dehydration of diaspore and goethite during low temperature heating as criterion to separate unheated from heated rubies and sapphires |
| topic | ruby sapphire low-temperature heating diaspore goethite Raman |
| url | https://www.mdpi.com/2075-163X/13/12/1557 |
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