Fossilium

Fossilium is a term used in paleontology to describe a distinctive fossil-preserving material recognized in some sedimentary rocks. It denotes mineralized deposits that enclose and reveal fine details of ancient organisms, including soft tissues, that are not usually preserved in ordinary fossils.

Fossilium forms during diagenesis when silica- and phosphate-rich fluids migrate through buried organic matter. Mineral replacement and infilling around the decaying tissues produce microcrystalline silica, calcium phosphate, and iron-bearing phases that retain cellular outlines and sometimes three-dimensional structures. The result is a hard, glassy to pearly material that preserves microstructures at high fidelity.

Fossilium has been reported in several globally distributed sedimentary basins, most often in fine-grained limestone, marl, and shale layers with high fossil content. It is valued by paleontologists for its potential to yield preserved soft-tissue impressions, cellular patterns, and isotopic signatures that illuminate ancient ecosystems and environmental conditions.

Researchers employ micro-CT scanning, electron microscopy, and isotopic analyses to study Fossilium. Some debates persist over the relative contributions of biogenic versus abiogenic processes in its formation, and about the taxonomic scope of organisms that it preserves. Nevertheless, it is considered a valuable, though rare, source of paleobiological information.