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Dissolved elements and compounds produced during chemical weathering
follows a different path. This material is transported down the stream
to the ocean but is not deposited. Organisms aid in the creation of
chemical sedimentary rocks. Sometimes the ions of SiO2 or
CaCO3 are absorbed by organisms. They use the minerals to
create their shells or skeletons. Most skeletons are composed of the
mineral aragonite (a form of calcite) or opal (a form of quartz).
After a fossiliferous sedimentary rock forms, the minerals that make
up the fossils may undergo recrystallization. The crystals
dissolve and precipitate when conditions are right.
Recrystallization destroys the original fossils and produces chemical
sedimentary rocks.
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