petrified fossil
forms when the entire organism or parts of it are trapped in tar or ice and more which prevents the fossil from decaying.
cast fossil
forms when a mold fossil is filled with sand that hardens into the shape of the organism
mold fossil
forms when sediments bury a organism and the sediments change into rock and leaves a copy of the shape of the organism
Carbonized fossil
forms when organisms or parts of them are pressed between layers squeezing almost all the decaying organism away leave the carbon imprint on the rock.
trace fossil
forms when the mud or sand gardens to stone where a footprint trail or burrow of and organism was left behind.
index fossil
helps tell how old a fossil is