Ex limestones chert and evaporates limestonecomposed

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formed by chemical reactions occurring at/near Earth’s surface. EX: limestones, chert and evaporates. Limestone—composed of mineral calcite (CaCO3) Can be formed by organic (involving life processes) or inorganic chemical reactions—as  an example of an organic chemical reaction forming limestone—we go to the oceans Living near ocean surface are microscopic organisms like coccolithophorids and  foraminifera Coccolithophorids- are phytoplankton floating plants that are photosynthesizers Foraminifera are zooplankton – floating organisms that feed off other material In life processes, coccolithophorids and foraminifera take in seawater and precipitate out  (convert from liquid to solid) calcium (Ca 2+) and carbonate (CO 3   2+ ) – the calcium and  carbonate bond and form the mineral calcite this this is the material that makes their shells From lithified accumulations of organic  debris
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When these organisms die shells (encapsulated within fecal fish pellets) sink to bottom  of ocean floor—large quantities of these accumulate—as they get buried squeezed  tighter, water is squeezed out, eventually these shells lithified to form limestone The three most dominant types (95%) of sedimentary rocks:  Shales (70%)  Sandstones (20%) Limestones (10%)
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