1. FOSSILS!!!!
By: Patty Kittrell

2. How are fossils formed? Unaltered preservation
Permineralization (petrification)
Replacement
Carbonization (coalification)
Recrystalization
Authigenic preservation (casts or molds)

3. Unaltered preservation
Unaltered preservation is when amber or tree sap that has completely encased insects, spiders, and sometimes small lizards.
This is the preservation of chemicals such as aragonite, calcite, chitin, cellulose, and calcium phosphate, all the original material from the organism still remains.

4. Permineralization
The common name of this process is Petrification, this occurs when minerals like calcite, pyrite, or silica carried by water begin to fill the internal casts and other tissues in the organism. The minerals in the porous walls start harden then crystalize, leaving the animal preserved as rock.
You commonly see this as petrified wood or bone!

5. Replacement
Unlike unaltered preservation , in replacement the original hard parts of the organism are dissolved away. The organic material is replaced by minerals like silica and pyrite this happens on an atom to atom ratio.
Silica is usually found in replacement fossilization when the original material was aragonite and cacite this happens in oxidizing and acidic conditions. Pyrite on the other hand happens in reducing conditions when oxygen is absent in an atom for atom substitution. This is usually not a destructive process.

6. Carbonization
Also known as distillation, is fossilization of soft bodies including plants, fish, and reptiles. This is a decomposing process when all other elements like hydrogen, oxygen, and nitrogen are removed leaving only carbon.
Identifying carbonization is easy! It is the shiny black/brown carbon film left behind in the fossil impressions.

7. Recrystallization
Generally a pretty destructive process, this happens after time and pressure the original organic material is transformed into more stable minerals, or the smaller transform into larger crystals. Micro-structures are usually preserved while there is loss of all the original material.

8. Authigenic preservation
This type of preservation refers to impressions, molds, and casts of an organism that has previously been decomposed. This process begins when organisms are entrapped in sedimentary rock usually in course porous rock that allow water to dissolve the original organism.

9. Reference Page
2003/1fossil&taph&ichno.htm ml
ssils/Fossilhow.html
rocks.html
finds.com/how_are_fossils_formed.html