Cracking of Gem Opals
نویسندگان
چکیده
The value of gem opals is compromised by their potential susceptibility to “crazing”, a phenomenon observed either in the form whitening or cracking. To understand latter, 26 opal samples were investigated and separated into 2 groups based on handling: “water-stored” samples, which are stored water after extraction, “air-stored” air for more than year. induce cracking, thermally treated staged heating characterized using optical microscopy Raman spectroscopy before For water-stored opals, cracking was initiated with moderate up 150 °C, while air-stored higher temperatures, circa 300 required. In that cracked, polarized light revealed stress fields remaining around cracks, red shift bands suggested tensile stresses. These stresses not cracked. Based these observations, ascribed super-heated water-induced decrepitation. By contrast, linked drying shrinkage, correlates anecdotal reports from trade. We thus identify physical origin comparing it current knowledge, we determine factors leading
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ژورنال
عنوان ژورنال: Minerals
سال: 2023
ISSN: ['2075-163X']
DOI: https://doi.org/10.3390/min13030356