lithified

/ˈlɪθɪfaɪd/
adjective
  1. Turned into rock; describing sediment that has become solid rock through natural processes.
    • Hikers walked across a lithified lava flow that had cooled and hardened thousands of years ago.
    • Fossils are often found in lithified mud that was once soft and wet.
    • The lithified sand dunes now form a beautiful red sandstone cliff.
Synonyms
verb
  1. Past tense of lithify: to have turned into rock.
    • Scientists studied how the ancient seabed lithified under the weight of glaciers.
    • The volcanic ash lithified quickly after being buried by later eruptions.
    • Over millions of years, the sediment lithified into a hard layer of limestone.