Mineralogical Characteristics of Natural Semiconducting Minerals in Danxia Red Layers of Lang Mountain, Xinning, Hunan Province, China

XIAO Yuxiong, LI Yanzhang, DING Hongrui, LI Yan, LU Anhuai†

Abstract After fieldwork, metallic minerals in the samples collected from the red layers of Danxia located in Lang mountain, Xinning, Hunan province, were characterized by complementary methods, including Polarizing Optical Microscope (POM), Environmental Scanning Electron Microscopy (ESEM), Energy Dispersive X-ray analysis (EDX), High Resolution Transmission Electron Microscopy (HRTEM), Electron Probe Micro-analysis (EPMA), micro-area X-ray Diffraction (XRD), micro-raman spectra (μ-raman), and X-ray fluorescence (XRF), either by in situ analysis or powder analysis. The dominant natural semiconducting minerals from the red layers of Danxia were hematite and anatase. In addition, the contents of iron and titanium in the red layers were 2.8 times and 2.4 times higher than that of the non-red layers, respectively. Mineralogical investigation revealed that the majority of Fe/ti oxides were presented like cementating coarse silicate minerals (feldspar, quartz and biotite), suggesting these Fe/ti oxides were formed exogenically after weathering and eluviation of Fe and Ti-bearing silicate minerals (ilmenite and biotite). Semiconducting properties exhibited by exogenic hematite and anatase in the red layers of Danxia can provide fundamental information to further study the photocatalytic properties and environmental effects of the Danxia red layers, and to understand the interrelationship between the Cretaceous oceanic red bed and continental red bed on the Earth’s surface. Key words Danxia landform; iron oxide; titanium oxide; characteristics of mineral