Why do fossils appear in sedimentary rocks?
Sedimentary rocks are built up from compressed sediment–the mud and other gunk found at the bottom of rivers, lakes, etc. Any bones that happen to be embedded in that mud will be fossilized. Fossils don’t appear in igneous or metamorphic rocks because these rocks are formed under conditions of heat and pressure that would destroy any organic material (or preexisting fossils) that might be present.
