Cuprite and Malachite in Agate from the Yanyuan Region, Sichuan
The Yanyuan region in China’s Sichuan Province is rich in agates known for their vibrant colors, including pink, purple, and green. Dendritic inclusions are common in agates from many areas but rarely seen in agates from Yanyuan. Recently, our interest was drawn to a 9.40 g gray-purple carved pendant submitted for identification (figure 1) that displayed peculiar dendritic inclusions. The piece was reported by the client to be from Yanyuan.
Standard gemological testing of the pendant yielded a spot refractive index of 1.54, and Fourier-transform infrared (FTIR) spectroscopy was used to confirm the identity of the pendant. Microscopic observation revealed a blue-green spherical mineral surrounded by copper-red dendritic inclusions (figure 2), which appeared to have a metallic luster under reflected light.
The red inclusions in the exposed surface and the blue-green inclusion nearby were analyzed with Raman spectroscopy. The analyses showed that the red inclusions were cuprite (Cu2O) and the blue-green sphere was malachite (Cu2(CO3)OH2), both of which were confirmed by energy-dispersive X-ray fluorescence (EDXRF) testing (figure 3). In the Raman spectra of the inclusions, the peak at 464 cm–1 was assigned to the agate host (figure 3).
While copper inclusions have been previously reported in purple chalcedony (Spring 2019 G&G Micro-World, p. 111) and chrysocolla chalcedony (M. Ye and A.H. Shen, “Gemmological and mineralogical characteristics of chrysocolla chalcedony from Taiwan, Indonesia and the USA, and their separation,” Journal of Gemmology, Vol. 37, No. 3, 2020, pp. 262–280), this is the first time we have identified two kinds of copper-bearing inclusions in agate from Yanyuan.
