Which type of rock commonly contains fossils?

Concept

Fossils are preserved when the remains or traces of organisms are buried by sediment and become rock without intense heating. This preservation process therefore occurs most commonly in sedimentary rocks.

Application

Layers of sediment can rapidly bury shells, bones, leaves, or traces and protect them while compaction and cementation form rock. Igneous rock forms from molten material, whereas metamorphic rock undergoes substantial heat and pressure; those conditions generally prevent or destroy fossil preservation.

Contrast

• Sedimentary rocks: deposition and burial provide the usual setting for fossil preservation.

• Metamorphic rocks: heat and pressure usually alter or destroy fossil evidence.

• Igneous rocks: formation from magma or lava involves temperatures unsuitable for preserving remains.

• More than one of the above: rare exceptions do not make multiple listed rock classes commonly fossil-bearing.

• None of the above: the standard fossil-bearing rock class is present among the choices.

Cross-check

USGS and National Park Service geology resources identify sedimentary rocks as the rocks in which fossils are found most commonly or almost exclusively.

Result: sedimentary rocks.