Wiktionary
lithify
vb. To turn sediment into solid rock
Usage examples of "lithify".
Immediately, she began to roam, examining the stalactites that hung from the ceiling, still forming, still dripping with water, each drop leaving a minute quantity of calcium which would harden and lithify, gradually growing the inverted steeple of mineral deposits longer and longer.
For example, a set of footprints was once laid down in muddy ground that got covered over and lithified as shale.