Microscopic examination of a transparent contact-twinned calcite crystal from the Jiepaiyu mine in Shimen County, Changde, Hunan, China, revealed vivid red to orange-red blebby to platy realgar (As4S4) inclusions scattered throughout the host, consistent with calcite’s common e-twin law (see above). Raman microspectroscopy was targeted directly on the red inclusions using 785 nm excitation over shorter wavelengths. This approach was followed since the light-induced realgar-to-pararealgar conversion is reportedly most efficient under ~500–670 nm and is markedly decreased at longer wavelengths (>~670 nm) (D.L. Douglass et al., “The light-induced alteration of realgar to pararealgar,” American Mineralogist, Vol. 77, No. 11-12, 1992, pp. 1266–1274). The resulting spectrum showed calcite bands together with diagnostic realgar bands. The occurrence of well-preserved realgar inclusions within transparent contact-twinned calcite is mineralogically noteworthy given realgar’s tendency to alter under prolonged light exposure.
Wingtak Lui and Rui Rui Xing are affiliated with Min De Minerals & Gem Research Co., Ltd. in Nanjing, China. Yu-Chen Huang is affiliated with Taiwan Central Gem Laboratory Co., Ltd.
Microscopic examination of a transparent contact-twinned calcite crystal from the Jiepaiyu mine in Shimen County, Changde, Hunan, China, revealed vivid red to orange-red blebby to platy realgar (As4S4) inclusions scattered throughout the host, consistent with calcite’s common e-twin law (see above). Raman microspectroscopy was targeted directly on the red inclusions using 785 nm excitation over shorter wavelengths. This approach was followed since the light-induced realgar-to-pararealgar conversion is reportedly most efficient under ~500–670 nm and is markedly decreased at longer wavelengths (>~670 nm) (D.L. Douglass et al., “The light-induced alteration of realgar to pararealgar,” American Mineralogist, Vol. 77, No. 11-12, 1992, pp. 1266–1274). The resulting spectrum showed calcite bands together with diagnostic realgar bands. The occurrence of well-preserved realgar inclusions within transparent contact-twinned calcite is mineralogically noteworthy given realgar’s tendency to alter under prolonged light exposure.
Wingtak Lui and Rui Rui Xing are affiliated with Min De Minerals & Gem Research Co., Ltd. in Nanjing, China. Yu-Chen Huang is affiliated with Taiwan Central Gem Laboratory Co., Ltd.
