Chemical sedimentary rocks

derived from material carried in solution to lakes/seas

evaporation and precipitation from solution to form “chemical sediments”

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 RocksPrecipitation:

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)

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

Chemical sedimentary rocks(Precipitation)

composed primarily of calcite (calcium carbonate CaCO3)

10% of all sedimentary rocks (by volume)

most abundant chemical sedimentary rock

formed by marine organisms (corals, clams, algae)

some deposited directly out of ocean or other waters

Most abundant chemical precipitate rock which forms in shallow marine waters. Often contain shell fossils.

1) Limestone

Sedimentary rocks

Coral reef limestone 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

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.

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.

Chemical sedimentary rocks(Precipitation)

3) Travertine

Sedimentary rocks

Stalactite: icicle-like pendants that hang from the ceilings of caverns and form where water seeps through cracks above.

Stalagmite: mound shaped deposits that form on the floors of caverns and build upwards toward the ceilings.

Chemical sedimentary rocks(Precipitation)

3) Travertine

Chemical sedimentary rocks(Evaporation)

Evaporites

Salt (Halite), Gypsum and Sylvite

water evaporates and dissolved stuff is deposited

mostly marine (ocean) rocks, but some lakes

Salt flats, Utah Death valley, Calif.

Sedimentary rocks

Chemical sedimentary rocks(Evaporation)

Evaporites water evaporates and dissolved stuff is deposited

Sedimentary rocks

Chemical Sedimentary RocksExamples 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 RocksExamples of chemical sedimentary rocks include;

5) Rock GypsumConsist 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)

Environment Rock types

Shallow Marine - gypsum, halite (rock salt), sylvite, limestone, dolomite

Deep Marine/ocean - limestone, dolostone, chert

Cave - travertine (stalactites and stalagmites)

Chemical sedimentary rocks(Biochemical)

Biochemical Sedimentary rock created when organisms use materials dissolved in air or water to build their tissue.

Examples include;-- Coquina-- Chaulk-- Chert-- Limestone (Coral)-- Coal

Sedimentary rocks

Chemical sedimentary rocks(Biochemical)

Organic rock of biochemical origin Rock of shell fragments

Sedimentary rocks

6) Coquina

Sedimentary rocks

most formed in ocean

very fine grained silica

also called flint, jasper, agate

occurs as layers (beds) & as irregular blobs in limestone

marine creatures remove silica from sea water, make shells

Agate

Chemical sedimentary rocks(Precipitation)

7) Chert

Chemical sedimentary rocks(Biochemical)

Sedimentary rocks

10) Coal the end product of large amounts of plant material that has been buried and chemically altered over millions of years.

8) Limestone (Coral) formed as a result of organisms creating limestone from their shells.

9) Chaulk formed as a result of the build-up, compaction, and cementation of microscopic marine organisms (ex. Foraminiferia).

Biochemical Sedimentary Rocks and Depositional Environments

(Summary)

Environment Rock types

Swamp - coal

Shallow Marine - coquina, limestone (coral)

Beach - coquina

Deep Marine - chaulk, chert

Sample ProblemDescribe 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.