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SEDIMENTARY ROCKS
Lesson 2 - Page 4

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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. 


Lithographic Limestone - a recrystallized 
fossiliferous sedimentary rock


Opaline (form of quartz)

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