In this study, the geochemical characteristics of obsidian were compared through mineralogical and geochemical analysis using obsidians from Baekdusan and Kyushu, Japan. As a result, the mineralogical characteristics as well as the major elements, minor elements, and trace elements of Baekdusan and Kyushu obsidians, were identified and these characteristics that can be distinguished by region. In addition, the standard range of quantitative values for obsidians according to the analysis method for obsidians by region was presented, and which is expected to be used as a new chemical discrimination scheme for interpreting the provenance of obsidian artifacts. The results of the geochemical analysis of obsidians were compared with each other through various analysis, and the applicability to the neutron activation analysis for obsidians was examined. As a result, it is expected that the whole rock quantitative analysis using INAA/PGAA of obsidians can be possible as a good discriminator of the distinct sources by confirming high accuracy in the major elements and trace elements. In particular, the high accuracy of the major elements analysis in PGAA and the quantitative analysis of light elements such as boron and chlorine suggest the possibility of comparing the characteristics of volcanic rocks by region. The comparison with the results of ICP-MS shows that the 11 elements in NAA have a high resolution. Among them, elements like Rb, Ce, Nb, Sm, Tb, Dy, and Th may be applied as a characteristic elements that can distinguish between Baekdusan and Kyushu obsidians. However, discrepancies between whole rock analysis and spot analysis results are found depending on the analysis method due to the presence of microlites contained in obsidians. In the case of the FE-EPMA analysis, it is appropriate to interpret the spot analysis and the whole rock analysis separately because since analysis errors may occur depending on the overlapping of the major elements and the amounts of microlites. However, in the case of LA-ICPMS, the beam size to be analyzed is sufficiently large, so even if it is a spot analysis of the matrix, the discrepancies between the composition of whole rock analysis is considered to be negligible.
In the geochemical analysis of obsidians, the necessity of developing a geological reference material to obtain accurate and precise quantitative values was increased, and the geological standard sample was produced and developed using Korean granite rocks. However, due to the disadvantage that it is expensive and difficult to obtain, it is necessary to develop a geostandards using Korean rocks. For this reason, three representative granite samples were selected and conducted petrological observation to establish the Korean geostandards. Samples were taken from the two Jurassic (KJG-1, KJG-2) and one Cretaceous (KCG-1) granites in South Korea. The powder samples were prepared by the standard pulverization process, and glass beads were made for geochemical analysis using X-ray fluorescence (XRF) method, and finally, major element contents of the samples were acquired. The analytical data are shown with mean, standard deviation and relative standard deviation. The accuracy of the analysis was confirmed within an estimated error range of about 5% by comparing the recommended true values of the USGS and GSJ geostandards. In addition, I checked the analytical precision by calculating a relative standard deviation of about 3% from the XRF analytical results for the three samples.
Glass reference materials have been essentially used for precise geochemistry analytical techniques. In order to make up for the drawback of synthetic glass reference materials, which have the high uncertainty caused by the difference in composition of natural rocks, and introduce a glass geostandard using natural glass. The NK-B1 sample, which comes from the Baekdusan obsidian, is a natural glassy rock that contains only few crystals such as microlites or inclusions. In this study, I examined the feasibility of the sample as a reference material for microanalysis like EPMA or LA-ICPMS, and a quantitative value for it was suggested as a recommended value. This glass reference sample and quantitative values are expected to be used as a standard sample to confirm the accuracy of the analysis in microanalysis and to distinguished between Baekdusan and Kyushu, Japan.