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Types of Rock Fossils

Fossils are the preserved remains or imprints of plants and animals that lived hundreds or thousands of years ago. They can be found all over the world in lava, sediment, tar, mineral deposits or amber and can range in size from microscopically small to the size of large dinosaurs. In rare cases, whole animals can be preserved through a natural mummification process.

Mold Fossils
- Mold fossils occur when sedimentary rock or lava form around a plant or animal, which then decays. The result is a cast imprint in the rock in the form of the captured plant or animal. The rock mold can be used to create a model of the organism.
Cast Fossils
- This ancient mollusk fossil was created over thousands of years through a casting process.
  
  Cast fossils are created when a natural substance fills the core of a mold fossil and then solidifies. This creates an identical rock formation in the shape of the original organism which the mold was created around.
Imprint Fossils
- Imprints are impressions that a living thing makes in a substance which then solidifies into a fossil. The most common imprints are footprints or other tracks an animal makes when walking across sand or clay. If left undisturbed these imprints can harden into rock fossils.
Petrification Fossils
- The most common example of petrified fossils are found in petrified forests.
  
  Wood or dead animals can be turned into fossils through a process called petrification in which the water in the organism's cells is replaced with minerals. Over time, the creature is transformed entirely into a permanent stone-like substance.
Whole Animal Fossils
- Amber is tree sap that has solidified over thousands of years.
  
  Fossilized remains of entire insects, birds, plants and small animals have been preserved whole in tree sap, tar or ice. Because the organisms are completely encased in a hard and impermeable substance, they do not decay and are not altered by the air, water or minerals in the environment.

Fossil Collecting