Very nice big specimen with large (for the locality), clear quartz crystals with inclusions of fossil fungi mycelia respectively archaea bacteria. Fossil stromatolites built from or including threads of bacteria and/or fungi mycelia with quartz crystals. Worldwide singular geological phenomenon in the Sauerland area. Here's an extract from a German publication: "Fossil fungi in iron stromatolites from Warstein (Rhenish Massif, Northwestern Germany) Zeitschrift Facies Verlag Springer Berlin / Heidelberg ISSN 0172-9179 (Print) 1612-4820 (Online) Heft Volume 7, Number 1 / Dezember 1982 DOI 10.1007/BF02537228 Seiten 237-259 Fossil iron stromatolites, formed by fungi, have been found near Warstein, W. Germany. The stromatolitic and massive ferruginous quartzes are always confined to karstic hollow molds of the Devonian "Massenkalk". The few occurrences show that these are chalcedony-quartz-silicifations of mainly ac-oriented, corrosively widened cracks. A mineralization temperature of about 120°C was found by microthermometrical measurements. Druses in ferruginous quartz sometimes carry clear, prismatic to pseudocubic quartzes embedding fungal mycelia. The fungal filaments are generally encrusted with goethite and appear in stromatolitic, massive and patch-like forms. An Oligocene/Miocene age is presumed ... " Newer texts suggest that the fossil inclusions are threads of bacteria archaea. For sure the fine threads we see are of organic origin, and in my opinion, these are clearly mycelia fossils. Hohenlimburg is the same geological setting as Warstein. Some of the best 'fossil inclusion'-quartz crystals I've seen so far.