Abstract
Abstract In this paper, we report on electron microscopy studies of single crystals of the natural mineral lorándite, TlAsS2. The main focus of this investigation was to address the question as to whether those lorándite crystals are chemically and structurally homogeneous, in order to be utilized as an effective neutrino detector within the lorándite experiment (LOREX) project. Apart from few secondary minerals, being present only at the surface of the lorándite samples, scanning electron microscopy (SEM) indicated homogeneous crystals. Similarly, transmission electron microscopy (TEM) imaging revealed a homogenous and undisturbed crystal structure, with the only exception of local coffee-bean contrasts; however, rarely observed. These specific contrast variations are known to be a typical strain indicator caused by a local deformation of the crystal lattice. Energy-dispersive X-ray spectroscopy (EDS) in conjunction with electron energy-loss spectroscopy (EELS) did not show any significant chemical difference when analysing regions on or off those coffee-bean features, indicating a chemically homogenous mineral. Since the presence of lattice disturbing secondary phase precipitates could be excluded by imaging and complementary chemical analysis, crystal defects such as dislocations and stacking faults or minor fluid inclusions are discussed as the probable origin of this local elastic strain. The experimental results confirm that the studied lorándite single crystals fulfil all structural and chemical requirements to be employed as the natural mineral that allows to determine solar neutrino fluxes. In addition, critical issues regarding the rather challenging sample preparation of lorándite are reported and a quantification of the maximum tolerable electron dose in the TEM is presented, since lorándite was found to be sensitive with respect to electron beam irradiation. Furthermore, the limits of EDS measurements due to peak overlapping are shown and discussed utilizing the case of Pb in lorándite. In this regard, a comparison with the Tl- and Pb-containing natural mineral hutchinsonite, TlPbAs5S9, is also included.
Highlights
The monoclinic thallium sulfosalt mineral lorándite, TlAsS2, was first described by József Krenner in 1894, based on samples from the epithermal Sb-As-Tl-Au deposit of Allchar in Macedonia, where it was mined and smelted as a thallium ore at that time [1]
In this paper, we report on electron microscopy studies of single crystals of the natural mineral lorándite, TlAsS2
The experimental results confirm that the studied lorándite single crystals fulfil all structural and chemical requirements to be employed as the natural mineral that
Summary
The monoclinic thallium sulfosalt mineral lorándite, TlAsS2, was first described by József Krenner in 1894, based on samples from the epithermal Sb-As-Tl-Au deposit of Allchar in Macedonia, where it was mined and smelted as a thallium ore at that time [1]. Due to the three cleavage planes of (100) excellent, (201) very good and (001) good, lorándite crystals very separate into cleaved pieces or rather thin lamellae which can be plastically deformed [3, 4]. The crystal structure of lorándite (shown in Figure 1(a) and (b)) was first described by Zemann and Zemann in 1955 [3], slightly corrected and refined by Fleet [4] and later by BalićŽunić et al [5]. The (100) cleavage requires the disruption of one TI–TI interaction and two
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