u Chemical sedimentary rocks v derived from material carried in solution to lakes/seas v evaporation and precipitation from solution to form “chemical sediments” v These rocks can also form where ground water dissolves chemicals and precipitates the material in certain environments. An example of this process would be the formation of stalactites and stalagmites. Sedimentary rocks

Chemical Sedimentary Rocks These rocks form as a result of chemical weathering dissolving chemicals and transporting it in solution. When conditions are right, these dissolved chemicals change back into a solid through the processes of;  1)Precipitation 2)Evaporation.

Chemical Sedimentary Rocks Precipitation:  Evaporation:  Process where a change in environmental conditions cause chemicals dissolved in solution, to fall out of solution and forms a solid material. Most common in shallow water environments. Process where there is a change in state from a liquid to a gas. Chemicals dissolved in the liquid (water) are left behind as a solid material. Note: Evaporation and Precipitation often work together. As water evaporates, chemicals in solution will precipitate. Example: Rock Salt (Halite) 

u Chemical sedimentary rocks (Precipitation) Precipitates  Temperature, Concentration, or Chemical changes.  Chemicals dissolved in solution, fall out of solution and forms a solid rock.  Results from a change in environmental conditions, such as; Sedimentary rocks

u Chemical sedimentary rocks (Precipitation) v composed primarily of calcite (calcium carbonate CaCO 3 ) v 10% of all sedimentary rocks (by volume) v most abundant chemical sedimentary rock v formed by marine organisms (corals, clams, algae) v some deposited directly out of ocean or other waters vMost abundant chemical precipitate rock which forms in shallow marine waters. Often contain shell fossils. 1) Limestone Sedimentary rocks

Coral reeflimestone mountain

Sedimentary rocks  Dolomite appears to form in many different types of environment  CaMg(CO3)2, Calcium Magnesium Carbonate  Dolomite is used as an ornamental stone and a concrete aggregate.  It is an important Petroleum reservoir rock u Chemical sedimentary rocks (Precipitation) 2) Dolomite

Sedimentary rocks  "Travertine" is sometimes used to mean cavestone, the calcium carbonate rock that makes up stalactites and other cave formations. v A kind of limestone deposited by springs.  Groundwater traveling through limestone beds dissolves calcium carbonate and as this dissolved matter precipitates it builds up travertine deposits. u Chemical sedimentary rocks (Precipitation) 3) Travertine

Sedimentary rocks v Stalactite: icicle-like pendants that hang from the ceilings of caverns and form where water seeps through cracks above. v Stalagmite: mound shaped deposits that form on the floors of caverns and build upwards toward the ceilings. u Chemical sedimentary rocks (Precipitation) 3) Travertine

u Chemical sedimentary rocks (Evaporation) Evaporites v Salt (Halite), Gypsum and Sylvite v water evaporates and dissolved stuff is deposited v mostly marine (ocean) rocks, but some lakes Salt flats, UtahDeath valley, Calif. Sedimentary rocks

u Chemical sedimentary rocks (Evaporation) Evaporites v water evaporates and dissolved stuff is deposited Sedimentary rocks

Chemical Sedimentary Rocks Examples of chemical sedimentary rocks include; 4) Rock Salt Consist of the mineral Halite.  Forms by evaporation of shallow seas and lagoons that have high concentrations of halite in solution. The mineral precipitates out of solution as the water evaporates.  Common use is table salt and road salt. 

Chemical Sedimentary Rocks Examples of chemical sedimentary rocks include; 5) Rock Gypsum Consist of the mineral Gypsum.  Forms by evaporation of shallow seas and lagoons that have high concentrations of gypsum in solution. The mineral precipitates out of solution as the water evaporates.  Common use is plaster and gyproc (drywall). 

Chemical Sedimentary Rocks and Depositional Environments (Summary) EnvironmentRock types Shallow Marine- gypsum, halite (rock salt), sylvite, limestone, dolomite Deep Marine/ocean- limestone, dolostone, chert Cave- travertine (stalactites and stalagmites)

u Chemical sedimentary rocks (Biochemical) Biochemical v Sedimentary rock created when organisms use materials dissolved in air or water to build their tissue. v Examples include; -- Coquina -- Chaulk -- Chert -- Limestone (Coral) -- Coal Sedimentary rocks

u Chemical sedimentary rocks (Biochemical)  Organic rock of biochemical origin  Rock of shell fragments Sedimentary rocks 6) Coquina

Sedimentary rocks v most formed in ocean v very fine grained silica v also called flint, jasper, agate v occurs as layers (beds) & as irregular blobs in limestone v marine creatures remove silica from sea water, make shells Agate u Chemical sedimentary rocks (Precipitation) 7) Chert

u Chemical sedimentary rocks (Biochemical) Sedimentary rocks 10) Coal v the end product of large amounts of plant material that has been buried and chemically altered over millions of years. 8) Limestone (Coral) v formed as a result of organisms creating limestone from their shells. 9) Chaulk v formed as a result of the build-up, compaction, and cementation of microscopic marine organisms (ex. Foraminiferia).

Biochemical Sedimentary Rocks and Depositional Environments (Summary) EnvironmentRock types Swamp- coal Shallow Marine- coquina, limestone (coral) Beach- coquina Deep Marine- chaulk, chert

Sample Problem Describe two conditions necessary for chemical sedimentary rocks to form. Answer: One of two processes must occur, that being chemical precipitation or evaporation of water. Their must also be an accumulation of chemicals within the water so it can fall out of solution and form solid chemical sedimentary rock. Example: Salt water has an accumulation of salt dissolved in the oceans. In shallow marine environments, where water evaporates, the salt (halite) precipitates and forms rock salt.