I am reading on the petrification process. I found that there are two processes which are permineralization and replacement. I am not sure I fully comprehend the difference between them. I wonder if someone could explain them to me in simple terms.

Am I right to understand that permineralization is where the minerals replace the space where the bones of animal (for examples) reside making a cast of what the organism looks like while replacement replaces the bones of that animal on a molecular level where each molecule of the the organism's bones are replacement by a molecule from the mineral i.e. the replacement process is transforming/converting the bones into another substance. Also do the molecules of bones cease to exist after they are replaced?

Thanks for your time.


1 Answer 1


Simply put permineralization is dissolved minerals filling in the existing pore space in fossilized material. Replacement is dissolved minerals replacing the existing minerals (calcium phosphate, calcium carbonate, etc.) in fossil material via atom by atom or molecule by molecule ion exchange. Often both can occur but permineralization can leave original material in the fossil while replacement does not.

Replacement can happen after permineralization, in which case most of the structure gets preserved (but not material) even though replacement occurs.

Keep in mind once the living cells are dead bone, wood, and even shell is full of tiny pores and holes that can get filled in. Think of a sponge, in permineralization the sponge gets filled in with stuff, in replacement the sponge slowly dissolves but gets replaced by something else dissolved in the water as it leaves charges behind.

  • $\begingroup$ Thank you for the detailed answer. I am still a bit confused. I understood what you said but when I look into YouTube videos they mention that in permineralization the remains of the animal (for example) can dissolve and then permineralization would fill the gap where the animal used to be like forming a cast of an available mold. From your answer I visualize that permineralization fills the bones of an animal so the animal bones are augmented with the filled material. So in my mind the end result is a composite of original bones material plus dissolved minerals. Am I wrong? $\endgroup$
    – Lynn B.
    Apr 24, 2022 at 2:37
  • $\begingroup$ Also in replacement, what happens to the original molecules of animal bones? Are they dissolved? Do they cease to exist? Do they leak out into soil? $\endgroup$
    – Lynn B.
    Apr 24, 2022 at 2:40
  • $\begingroup$ the original molecules dissolve into the ground water, which is were the replacing minerals come from. As I said both things can occur to a fossil, and bone is not a single material but a composite of several different things, permineralization replaces some of those things and not others. $\endgroup$
    – John
    Apr 24, 2022 at 3:24
  • $\begingroup$ This might be of interest to both you: Spider fossils from 22 million years ago may have been preserved by sulphur secreted by algae $\endgroup$
    – Fred
    Apr 24, 2022 at 9:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.