In which type of rock are fossils most likely found?

Fossils are most likely found in shale because it is a sedimentary rock formed from the accumulation of fine sediment, primarily clay. Sedimentary rocks are conducive to fossil preservation because they typically form in environments where organisms can be buried quickly, such as river deltas, lakes, or ocean beds. The fine particles in shale can encapsulate remains of plants and animals, allowing them to be preserved over geological time.

In contrast, basalt is an igneous rock formed from the rapid cooling of lava and typically does not contain fossils due to the high temperatures and molten state in which it forms. Slate, also a metamorphic rock, originates from shale but has undergone transformation under heat and pressure, which generally destroys any fossils that may have been present. Quartzite, another metamorphic rock that forms from sandstone, is similar in that it undergoes intense heat and pressure, which also typically precludes the preservation of fossils. This makes shale the most likely type of rock to contain fossils.