Petrographic and geochemical investigation of a stone adze made of nephrite from the site Balatonőszöd – Temetői dűlő (Hungary)

The present study reports on results of petrographic and geochemical analyses on a stone adze from the archaeological site Balatonőszöd – Temetői dűlő (Hungary). This is the largest excavated site of the Baden Culture in Hungary (more than 200.000 m2) and has the longest continuous settlement history. In the site, features of the Balaton-Lasinja Culture (Middle Copper Age) and the Boleraz Culture were also found. Altogether 500 stone artefacts were found and registered. The present study reports on the results of the investigation of a unique stone adze made of nephrite, found on the site. The nephrite adze found in Balatonőszöd – Temetői dűlő has proved to be the first find made of nephrite having an established archaeological context in Hungarian prehistory. By applying detailed petrographic, geochemical and petrophysical methods as well as comparing data from technical literature we located the origin of the raw material of the nephrite adze. Its most probable source is the Northern part of the Bohemian Massif, Lower Silesia, a geological site near Jordanów (Poland)

Origin of serpentinite-related nephrites from Gogołów-Jordanów Massif, Poland

The Gogołów-Jordanów Massif (GJM) in the Fore-Sudetic Block, SW Poland, hosts nephrites traditionally interpreted as serpentinite-related (ortho-nephrite). This contribution confirms the serpentinite-related origin of the nephrites on the basis of mineralogy, bulk-rock chemistry, and O and H isotopes. Rock-forming amphiboles from nephrites of the GJM have 7.73–7.99 Si apfu, comparable to 7.76–8.03 Si apfu of serpentinite-related Crooks Mountain nephrite amphibole (Granite Mountains, Wyoming, USA). The GJM amphiboles also have Mg/(Mg + Fe2+) values ranging from 0.82 to 0.94, similar to serpentinite-related Crooks Mountain and New Zealand nephrites amphiboles with Mg/(Mg + Fe2+) values of 0.86–0.90 and 0.91 to 0.92, respectively. The GJM nephrite amphiboles differ from the Val Malenco dolomite-related nephrite (Italy) amphibole, e.g., Val Malenco has a higher Si content (~8.0 Si apfu), although it overlaps with some of the GJM nephrite samples, and ~1.0 Mg/(Mg + Fe2+), also higher than the GJM samples. Also, apatite in the nephrite studied from the GJM has a slightly higher Ca content than apatite from dolomite-related nephrite. Chlorites found in the Jordanów nephrite have similar compositions to that of chlorites in the serpentinite-related nephrites and also to chlorites associated with serpentinisation/rodingitisation. The bulk-rock FeO vs. Fe/(Fe + Mg), Cr, Ni, and Co are also typical of the serpentinite-related nephrites. The d18O values range from +6.1 to +6.7‰ (±0.1‰), and the average dD values = –61‰, corresponding with the serpentinite-related nephrites range. Based on petrographic observations, we suggest four crystallisation stages (including rodingitisation prior to nephrite formation): 1 – leucogranite rodingitisation and black-wall formation; 2 – tremolite formation at the expense of rodingite diopside and black-wall chlorite (nephritisation) and garnet break-down, with spinel and chlorite formation (chlorite can be a product of garnet break-down or spinel with serpentine reaction); 3 – prehnite vein formation; 4 – tremolite formation at the expense of prehnite veins and actinolite veins formation. Spinels composed of 0.29–1.96 wt.% MgO, 24.87–29.67 wt.% FeO, 8.72–22.82 wt.% Fe2O3, 3.11–4.36 wt.% Al2O3, and 39.07–54.46 wt.% Cr2O3 suggest nephritisation in the greenschist to lower-amphibolite-facies conditions

Comparability of heavy mineral data – The first interlaboratory round robin test

Heavy minerals are typically rare but important components of siliciclastic sediments and rocks. Their abundance, proportions, and variability carry valuable information on source rocks, climatic, environmental and transport conditions between source to sink, and diagenetic processes. They are important for practical purposes such as prospecting for mineral resources or the correlation and interpretation of geologic reservoirs. Despite the extensive use of heavy mineral analysis in sedimentary petrography and quite diverse methods for quantifying heavy mineral assemblages, there has never been a systematic comparison of results obtained by different methods and/or operators. This study provides the first interlaboratory test of heavy mineral analysis. Two synthetic heavy mineral samples were prepared with considerably contrasting compositions intended to resemble natural samples. The contributors were requested to provide (i) metadata describing methods, measurement conditions and experience of the operators and (ii) results tables with mineral species and grain counts. One hundred thirty analyses of the two samples were performed by 67 contributors, encompassing both classical microscopic analyses and data obtained by emerging automated techniques based on electron-beam chemical analysis or Raman spectroscopy. Because relatively low numbers of mineral counts (N) are typical for optical analyses while automated techniques allow for high N, the results vary considerably with respect to the Poisson uncertainty of the counting statistics. Therefore, standard methods used in evaluation of round robin tests are not feasible. In our case the ‘true’ compositions of the test samples are not known. Three methods have been applied to determine possible reference values: (i) the initially measured weight percentages, (ii) calculation of grain percentages using estimates of grain volumes and densities, and (iii) the best-match average calculated from the most reliable analyses following multiple, pragmatic and robust criteria. The range of these three values is taken as best approximation of the ‘true’ composition. The reported grain percentages were evaluated according to (i) their overall scatter relative to the most likely composition, (ii) the number of identified components that were part of the test samples, (iii) the total amount of mistakenly identified mineral grains that were actually not added to the samples, and (iv) the number of major components, which match the reference values with 95% confidence. Results indicate that the overall comparability of the analyses is reasonable. However, there are several issues with respect to methods and/or operators. Optical methods yield the poorest results with respect to the scatter of the data. This, however, is not considered inherent to the method as demonstrated by a significant number of optical analyses fulfilling the criteria for the best-match average. Training of the operators is thus considered paramount for optical analyses. Electron-beam methods yield satisfactory results, but problems in the identification of polymorphs and the discrimination of chain silicates are evident. Labs refining their electron-beam results by optical analysis practically tackle this issue. Raman methods yield the best results as indicated by the highest number of major components correctly quantified with 95% confidence and the fact that all laboratories and operators fulfil the criteria for the best-match average. However, a number of problems must be solved before the full potential of the automated high-throughput techniques in heavy mineral analysis can be achieved