New data on halloysite of Ukraine

Abstract

Purpose. To study the features of a rare variety of halloysite found in the weathering crust of the Derenyukhinskiy gabbro-peridotite massif (located in the the Middle Pobuzhzhya, Southern Buh River region of Ukraine). Methodology. The study of samples was performed using several techniques: X-ray diffraction analysis (XRD), thermal analysis, optical microscopy, X-ray fluorescence analysis (XRF) and fluorescence spectroscopy. Findings. A rare chromium-containing variety of halloysite has been identified in the weathering crust of the Derenyukhinskiy gabbro-peridotite massif. Its remarkable features are blue colour, Cr2O3 content in the amount of up to 2.47% and luminescence under ultraviolet radiation. The study of the excitation and emission spectra showed that the maximum luminescence of this variety of halloysite occurs when irradiated with waves with a length of 367 nm, and the emission wavelength corresponds to the region of 390-500 nm, with a maximum at 424 nm. The studied sample was actually a mixture of two mineral species: halloysite (10Å) and halloysite (7Å) or metahalloysite. Aluminian chromite was identified in association with them, and impurities of kaolinite, clinochlore, quartz and goethite were detected. The formation of the mineral aggregate was due to chemical weathering of primary silicates and oxides, which were part of the rocks of the Derenyukhinskiy massif. Originality. Halloysite has been identified for the first time in the weathering crust of the Derenyukhinskiy gabbro-peridotite massif (Middle Pobuzhzhya). It was found that chromium-containing halloysite exhibits violet luminescence under ultraviolet radiation. The fluorescence spectrum of the mineral also has been studied. Practical implication. Detection of luminescence of chromium-containing halloysitemay be helpful in the use of composite materials made of this mineral, designed to remove chromium from wastewater.