Petrification – the
impregnation with minerals such as silica or calcite from
sediments which increases the weight and hardness of the
Replacement – where
the original material of the organism may have dissolved
and the space left filled with minerals from the surrounding
rocks. These can be very beautiful especially if the replacing
material is silica or pyrite.
Carbonization – the
process where the tissue of the organism may be converted
into a film
of carbon and can be seen in some plants and planktonic animals.