0 to become or to make something become a fossil (= something preserved in rock for a very long period):
The birds' bones are very fragile and tend to break down before they fossilize.
a fossilizing process in which wood is gradually replaced by silica
The dark contrast of the fossilized cell walls suggests that a light element (low atomic number), perhaps carbon, is still present.
However, this technique only provides an external morphological description of putative fossilized cells and is incapable of distinguishing between abiotic fossils of similar morphologies.
These methods, especially in relation to the theory of frames, have imported a new interest into a subject which was in danger of becoming fossilized.
The resulting structures (stromatolites) often undergo only moderate diagenesis and fossilize with characteristic biofabrics.
In the case of fossilized, older, adult learners this may be true.