CHARACTERIZATION OF OBSIDIAN FROM NORTH MACEDONIA (original) (raw)
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An Overview of the Analytical Techniques Applied to Study the Carpathian Obsidians
2019
In this paper, we give a brief overview of the analytical techniques applied on Carpathian obsidians, from the mid-sixties until present. Besides modern analytical techniques that are focussed especially on the determination of obsidian artefact provenance, microscopic methods are also applied: investigation in thin section under polarising microscope (flow fabric, inclusions, phenocrysts), characterization of individual microlites and trichites embedded in a glassy groundmass using microprobe, measurement of glass refractive index. Already in 1886, Gyula Szádeczky used the determination of specific gravity on Hungarian obsidians to describe black, translucent, green and red varieties. Magnetic susceptibility was used to distinguish obsidian tools from pieces of artificial glassy slag resembling to artefacts and found during field prospection. The presented methods are discussed according to their physical features, i.e. how the information obtained, elemental-, isotopicor structura...
In Eastern Slovakia obsidians were used most extensively during the Late Palaeolithic and Neolithic. Natural occurrences of obsidian are linked with products of rhyolite/rhyodacite volcanism, where they associate with perlite. Viničky, Malá Bara and Brehov are the known natural occurrences. Considering the present state of knowledge, the Brehov locality is a primary source of secondary obsidian ccumulations in Quaternary deluvial/fluvial deposits, partially covered by eolian sands, in the area of Brehov and Cejkov. Some of the macroscopic attributes, especially surface sculpture, of the obsidian cores from archeological sites resemble more those from the secondary accumulations. Conventional K/Ar dating of obsidians from natural occurrences and archeological sites implies multiple ages of natural sources. However, dating of obsidians at archeological sites points rather to a single source, or yet unknown source in addition to the secondary accumulations. Obsidians from at least two phases of rhyolite volcanic activity have been utilized for production of obsidian industry. Obsidians from the secondary accumulations in the area of Brehov and Cejkov apparently dominate at archeological sites and probably are equivalent to the subgroup C1a of the Carpathian obsidians.
Preliminary report on obsidian petrography from the Transcarpathian region in Ukraine
Natural Resource Environment and Humans, 2014
This paper reports the field occurrence, mineralogy, and whole-rock chemistry of the obsidian from the Neogen Carpathian volcanic arc area. The study area encompasses the Transcarpathian (Zakarpattia) region in Ukraine. A mafic xenolith comprising of a plagioclase, amphibole, and olivine mineral assemblage was found from the obsidian in this area. SEM-EDS analysis indicates that the olivine has high magnesium content. The forsterite (Mg2SiO4) content varies from 77% to 80%. The chemical composition of plagioclase remains constant, and is enriched in calcium. The anorthite (CaAl2Si2O8) content varies from 89% to 94%. The amphibole is classified into the tschermakite following the nomenclature of Leake et al. (1997). Based on the compositions of the amphibole and the plagioclase, pressure and temperature conditions of the mafic xenolith were estimated to be 4.5–7.9kbar and 1185–1358°C respectively. These results indicate that this mineral aggregate is not genetically associated with the rhyolitic magma from which the obsidian was derived, but is considered to be of an exotic xenolith originated from the gabbroic rocks of the lower crustal level of the Carpathian volcanic arc. The finding of mafic xenolith will help in characterizing the obsidian from this area, and is a key in understanding the tectonic and evolutionary history of the Carpathian volcanic arc.
Chemical, mineralogical and structural features of native and expanded perlite from Macedonia
Geologia croatica, 2019
The physico-mechanical, chemical and mineralogical characteristics of volcanic glass (perlite) from the Mariovo region (Macedonia) as well as the mineralogical changes that occur during its thermal treatment were investigated to demonstrate its utilization for industrial use. The native perlite was characterized by chemical analysis, X-ray powder diffraction (XRPD), infrared (IR) spectroscopy, thermal analysis (TGA/DTA), scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), and solid- state NMR. The chemical examination suggests that the perlite represents an acidic volcanic rock with a high percentage of SiO2 (72.45%), high in alkali metal oxides (4.21 wt.% K2O, 3.56 wt.% Na2O), with a loss of ignition 3.54 wt.%. Results from the XRPD indicated major amorphous behaviour, with low amounts of feldspars, quartz, and cristobalite. SEM examinations revealed glassy structure with presence of certain pores (dimensions ranging from 50–100 μm). The determined expansion coefficient was 20 times its original volume. XRPD of expanded perlite compared to the native perlite depicted new intensive peaks of cristobalite. SEM and TEM revealed irregular morphology with broken or ragged edges. On the basis of the chemical and mineralogical composition, the studied perlite is classified as an appropriate material suitable as ceramic flux to lower the sintering temperature.