What happens to an igneous rocks that makes finding fossils in them likely

Igneous rocks are known as metamorphic rocks. They are formed from hot lava so  it is highly unlikely that any fossils or remnants of a living organism are formed in igneous rocks. The majority of fossils are found in sedimentary rocks. Fossils formed when a layer of sediment covers dead plants and animals. This layer of sediment protects the fossil from rotting. In other words, the sediment preserves the dead animal or plant. With time, it turns into a fossil. Rocks such as limestone, sandstone and shale are the best rocks to find fossils in.