The empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater.
Minerals precipitate from the groundwater, occupying the empty spaces.
The totality of fossils is known as the fossil record.
Paleontology is the study of fossils: their age, method of formation, and evolutionary significance.
For permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decay process.
The degree to which the remains are decayed when covered determines the later details of the fossil.
If this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved.
Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization.
A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates.
Some fossils are biochemical and are called chemofossils or biosignatures.
Permineralization is a process of fossilization that occurs when an organism is buried.
Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. In some cases the original remains of the organism completely dissolve or are otherwise destroyed.
The remaining organism-shaped hole in the rock is called an external mold.
Specimens are usually considered to be fossils if they are over 10,000 years old.