ONCOID FLINT FROM THURINGIA (GERMANY) AND SILESIA (POLAND): A Gemmological Study and Lapidary Workshop of a Unique Silicified Fossil

This study explores the gemmological potential and lapidary characteristics of Oncoid Flint (oncolitic chert) from the Middle Triassic of Thuringia (Germany) and Silesia (Poland). The author provides a comparative analysis of two distinct varieties: the high-contrast, jet-black Thuringian material and the translucent, honey-colored Silesian erratics. The paper details the technical challenges of the lapidary process—specifically addressing the hardness differential between the silica matrix and calcareous oncoids—and offers practical solutions to prevent "undercutting" during polishing. By combining paleontological origins with artistic application, the study positions Oncoid Flint as a unique, high-value material for jewelry and gemstone collecting. Multimedia documentation of the workshop process is included as a supplemental resource.