Mineralogical and geochemical characterization of the "bituminous" agates from Nowy Kosciol (Lower Silesia, Poland)
Dumańska-Słowik, Magdalena; Natkaniec-Nowak, Lucyna; Kotarba, Maciej J.; Sikorska, Magdalena; Rzymełka, Jan A.; Łoboda, Agata; Gaweł, Adam
published: Apr 1, 2008
ArtNo. ESP154018403003, Price: 29.00 €
The agates from Nowy Kościół (Lower Silesia) exhibit mainly monocentric, horizontally stratified structures often developed as typical multiradial stars. The agates occurring in this region are usually spherical, shaped with diameters from 2 to 40-70 centimetres. Most of them are brownish red, honey-black or red. The dark colour of their bands is mainly caused by the occurrence of Fe-compounds, REE-bearing minerals, Zn sulphides and organic matter. The content of the latter one is relatively low (0.15 wt%), however it is strongly dispersed within the silica matrix. It forms thin laminae or irregularly shaped drops or lenses. The composition of bitumens is dominated by asphaltenes (56 wt.%) and the contribution of remaining fractions varies between 10% (aromatic hydrocarbons), 16% (resins) and 18% (saturated hydrocarbons). The stable carbon isotope analysis (saturated hydrocarbons = −28.9‰; aromatic hydrocarbons = −28.3‰; resins = −28.6‰; asphalthenes = −28.3‰; whole organic matter = −25.9‰) revealed its algal or mixed, algal-humic origin.