Hyalite Opal from Erongo, Namibia, Showing Green Daylight Fluorescence

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Authors

HANUS Radek SOBEK Kamil JOHNOVÁ Kamila TROJEK Tomáš ŠTUBŇA Ján HANUS Tomáš JUNGMANNOVÁ Kamila

Year of publication 2022
Type Article in Periodical
Magazine / Source Journal of Gemmology
MU Faculty or unit

Faculty of Science

Citation
Web https://gem-a.com/jog-volume-38-issue-2-2022
Doi http://dx.doi.org/10.15506/JoG.2022.38.2.172
Keywords Hyalite; Uranyl ion; Raman spectroscopy; Gamma spectroscopy; Photoluminescence
Description Rare hyalite opal showing green daylight fluorescence was discovered in the Erongo region, Namibia, sometime prior to 2000. Raman spectroscopy confirms this hyalite to be opal-A, and the most interesting feature of the Raman spectra are bands associated with the hydroxyl-stretching regions in the mineral’s structure. A doublet at 3602/3665 cm–1 appears to be unique to opal from this locality and may be due to the vibration of water in an unusual structural-binding arrangement. Trace amounts of the uranyl molecule (UO2)2+ are responsible for the luminescence, which is unevenly distributed according to the opal’s botryoidal structure. Measured radioactivity values are similar to those reported for other daylight-fluorescing opals (e.g. from Mexico), and are well below the global average terrestrial gamma dose rate.
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