Mineralogy and crystallographic properties of Heu-type zeolitic tuff from the Novakovic deposit, Bosnia and Herzegovina

Abstract

This paper presents mineralogical and crystallographic characterization of the zeolitic tuff from the Novakovic deposit, Republic of Bosnia and Herzegovina. The zeolitic tuff is of a whitish color composed of Ca-clinoptilolite and an amorphous phase (volcanic glass and amorphous SiO2). The zeolitic tuff was analyzed by X-ray diffraction of the polycrystalline sample (XRPD), scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), and differential thermal and thermo- gravimetric (DTA/DTG) methods. According to the results obtained, it can be concluded that the studied zeolitic tuff is composed of Heu-type minerals. Based on the chemical analysis, thermal treatment and XRPD analysis it was determined that this is a mineral Ca-clinoptilolite. Thermal analysis in the temperature range from 300 up to 700?C showed that the examined zeolite minerals from the Novakovic deposit are stable up to the temperature of 600?C. The crystal structure of Ca-clinoptilolite has been refined in the centrosymmetric space group C2/m (S.G. 12) with disordered distribution of Al and Si in the tetrahedral framework. The unit-cell parameters are as follows: a = 17.662 ?, b = 17.874 ?, c = 7.402 ?, ? = 116.32? and V = 2122.73 ?3. The basic structural motif is represented by four channels. Three channels are composed of eight-membered rings, and one of ten-membered rings. The ten-membered (channel A) and one eight-membered channel (B) are parallel to the crystallographic axis c, and the other eight-membered channel is parallel to the a-axis. Ca-clinoptilolite comprises approximately 90 % of the studied zeolite tuff while the rest 10 % is the amorphous phase. The overall cation exchange capacity (CEC) amounts to 187 mmolM+/100g, and calcium represents the most abundant cation in the studied sample. The atomic ratios of Si/Al, Na+/(Na++K+), and Ca2+/(Ca2++Mg2+) are as follows: 4.36, 0.14, and 0.55, respectively. The zeolite tuff is both thermally and structurally stable and has applications in various areas of industry and agriculture.