1. Permineralization or Mineralization

(Fossil Sharks Teeth)
Permineralization occurs when the pores of the plant or animal remains are impregnated by minerals. When this happens, the original shape of the object is not changed.

2. Petrifaction

(Pertified Wood)
Petrifaction is a type of permineralization. It occurs when the organic matter is completely replaced by minerals and the fossil turns to stone. Petrified wood is a common example of this.

3. Molds

(Fossil Fern leaf)
Molds types of fossils where the physical characteristics of organisms have been impressed onto rocks. The bodies decayed, leaving molds of the organism.

4. Casting

(Fossil Sea shells)
Internal molds form from hollowed structures when the interior of an organism is filled with inorganic material. When the shell deteriorates, an impression of the interior is left.

5. Impressions

(Dinosaur tracks and a leaf imprint)
Impressions are imprints of an organism. Impressions may be of plants or animals, or of tracks left by animals. Impressions are formed when mud or sediment in which they were made hardens into stone.

6. Desiccation, or Mummification.

(Insects trapped in amber)
Bones and tissues of organisms can be preserved, even keeping their natural colors. Desiccation occurs in areas void of moisture, such as insects trapped in tree sap which hardens to a stone called amber.

7. Dehydration

(Marsupial Lion from dry cave)
Also the desert or a dry cave can perserve an entire organism like this lion fossil. Dehydration occurs and the entire skeleton or organism is preserved.

8. Preservation

(Baby Mastodon)
The La Brea tar pits provide excellent examples of fossils which are of the whole organism. Numerous examples of organisms have been preserved there by asphalt, which preserves only the hard parts of the organisms. Bones, complete skeletons, insects, leaves, and flowers have been reclaimed from this site.

9. Freezing

(Frozen Mammoth and Tusks)
Freezing preserves a fossil of the highest quality. It preserves the organism with little alteration to the chemical composition. The temperature prevents little, if any, change to the organism.

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