What are some examples of biochemical sedimentary rocks?
The three basic types of biochemical (biogenic) sedimentary rocks are classified according to their original material: limestone (calcium carbonate), coal (carbon), and chert (silica).
Biochemical sedimentary rocks are biogenic, meaning that their material was gathered biochemically from the surrounding medium or substrate by certain types of organisms to form their skeletons or supporting framework. When the organisms died, their exoskeletons dropped down to the sea bottom and/or were deposited by waves and currents and became compacted into sedimentary rock over time.
Most limestones are formed from the exoskeletons of reef-forming corals, molluscs, and foraminiferans.
Coal is formed from the carbon in the buried organic material and wood of dead plants that did not decay (because of lack of oxygen) but got petrified over time.
Chert is rock formed from the siliceous ooze on the seabottom that accumulated from the glassy or siliceous skeletons of radiolarians and diatoms.