Mineral Inclusions in Sapphire from Basaltic Terranes in Southern Vietnam: Indicator of Formation Model

Vu, Doan Thi Anh; Salam, Abhisit; Fanka, Alongkot; Белоусова, Елена; Sutthirat, Chakkaphan

doi:10.5741/gems.56.4.498

Cited by 3 publications

(1 citation statement)

References 35 publications

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“…The samples contain typical inclusions from magmatic-related origin, such as feldspars, zircons, rutile, ilmenite, and Fe-rich inclusions [20][21][22][23][24][25][26][27][28] as shown in Figure 1. The cloud or minute particles of inclusions are scattered across the samples, especially in the area around planes of ilmenite inclusions.…”

Section: Samples and Heat Treatmentmentioning

confidence: 99%

Changes in Blue Color of Sapphire Compared with Oxidation State Changes

Amphon,

Chankhantha,

Srimuang

et al. 2024

Minerals

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Blue sapphire has long been treated with heat to modify its blue color and attain greater value. However, the process of modifying the blue color in sapphire remains not well understood. The color-changing mechanism has traditionally been explained using the Intervalence Charge Transfer (IVCT) (Fe2+-Ti4+ and/or Fe2+-Fe3+) theory, wherein the blue color can be diminished by heat treatment in an oxidizing environment which alters Fe2+ (FeO) to Fe3+ (Fe2O3) and decreases the occurrence of the IVCT process. However, recently, the band gap theory has been proposed, suggesting that iron (Fe) in sapphire is always in the Fe3+ state, the blue color is caused by Fe3+-Ti4+ pair and the heat treatment does not affect Fe oxidation state. Therefore, in this study, eight magmatic sapphires from four localities were investigated for changes in blue color via color analysis, changes in spectra using XANES, and changes in chemical composition using PIXE both before and after heat treatment. The color analysis reveals a slight reduction in saturation (fading of blue) and a noticeable lightening after heat treatment, which corresponds with the high content of solid inclusions or trapiche samples. XANES data analysis using the LCF technique indicated insignificant changes in Fe oxidation state from 2+ to 3+ after heat treatment across all samples. However, when comparing the XANES data with color parameter L*a*b*, it is noted that the percentage of Fe oxidation state changes does not show a positive relationship with changes in blue based on color parameter b* (blue–yellow); rather, it shows a positive relationship with parameter L* (lightness). Microscopic observations also reveal the dissolution of clouds or minute particles around planes of ilmenite needles. It could be suggested that the changes in Fe oxidation state may not be directly related to changes in blue color but could be linked to the partial dissolution of Fe-bearing inclusions.

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Section: Samples and Heat Treatmentmentioning

confidence: 99%

Changes in Blue Color of Sapphire Compared with Oxidation State Changes

Amphon,

Chankhantha,

Srimuang

et al. 2024

Minerals

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Trace element geochemistry and U-Pb dating of zircon inclusions in sapphire from Southern Vietnam: Indicator of basalt-related sapphire formation

Fanka

Sutthirat

2023

Journal of Asian Earth Sciences

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Variety of Iron Oxide Inclusions in Sapphire from Southern Vietnam: Indication of Environmental Change during Crystallization

Fanka

Salam

et al. 2021

Minerals

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Sapphires from alluvial deposits associated with Cenozoic basalts in Southern Vietnam were collected for investigation of mineral inclusions. In this report, primary iron oxide inclusions were focused on, with detailed mineral chemistry using a Raman spectroscope and electron probe micro-analyzer. Consequently, a variety of iron oxide inclusions were recognized as wüstite, hercynite, and ilmenite. Ilmenite falling within an ilmenite–hematite series ranged in composition between Il24-30He36-38Mt35-40 and Il49-54He34-40Mt7-10, classified as titanomagnetite and titanohematite, respectively. Wüstite with non-stoichiometry, (Fe2+0.3-0.9)(Ti3+<0.179Al3+≤0.6Cr3+<0.1Fe3+≤0.46)☐≤0.23O, was associated with hercynite inclusions, clearly indicating cogenetic sapphire formation. Wüstite and sapphire appear to have been formed from the breakdown reaction of hercynite (hercynite = sapphire+wüstite) within a reduction magma chamber. Titanohematite and titanomagnetite series might have crystallized during iron–titanium reequilibration via subsolidus exsolution under a slightly oxidized cooling process.

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Mineral Inclusions in Sapphire from Basaltic Terranes in Southern Vietnam: Indicator of Formation Model

Cited by 3 publications

References 35 publications

Changes in Blue Color of Sapphire Compared with Oxidation State Changes

Changes in Blue Color of Sapphire Compared with Oxidation State Changes

Trace element geochemistry and U-Pb dating of zircon inclusions in sapphire from Southern Vietnam: Indicator of basalt-related sapphire formation

Variety of Iron Oxide Inclusions in Sapphire from Southern Vietnam: Indication of Environmental Change during Crystallization

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