3 Types of Sedimentary Rocks

•Clastic•Chemical•Organic

Clastic Sedimentary Rock

• Sediments form when rocks are weathered and eroded

• Sediments are moved by wind, glaciers and water

• Most clastic sediments are deposited in the ocean

Clastic Sedimentary Rock

• Sediments are converted into solid sedimentary rock by the processes of compaction and cementation.

Clastic Sedimentary Rock

Compaction & Cementation

Clastic Sedimentary Rock

Compaction & Cementation

Clastic Sedimentary Rock

• Compaction occurs when the weight of overlying materials compresses the deeper sediments.

• Cementation occurs when soluble cementing materials, such as calcite, silica, and iron oxide, are precipitated onto sediment grains, fill open spaces, and join the particles.

Clastic Sedimentary Rock

•Particle (clast) size is key to type of rock–Gravel is > 2 mm–Sand is 1/16 mm to 2 mm–Mud is < 1/16 mm

•Clay is < 4 um•Silt is > 4 um

Sandstone

Conglomerate

Shale

Chemical Sedimentary Rock

• Chemical sedimentary rocks are made of mineral crystals that formed from chemicals dissolved in water.

• The water in the oceans, lakes, and underground is often full of dissolved minerals and other elements.

Chemical Sedimentary Rock

• When water is so full of elements that not all will fit, some are not able to remain dissolved.

• They come out of solution, or precipitate, forming solid mineral crystals.

• Precipitation is the opposite of dissolving.

Chemical Sedimentary Rock

• Minerals precipitate when some water has been evaporated or when a chemical reaction occurs.

• Evaporation takes only water molecules into the atmosphere so the elements in the remaining liquid water become very concentrated. Eventually, they do not all fit and some precipitate out as mineral.

Chemical Sedimentary Rock

Chemical Sedimentary Rock

• Inorganic Precipitates– Halite– Gypsum

• Organic precipitates– Limestone - (Calcite: a Calcium carbonate mineral)- CaCO3

– Dolomite - CaMg(CO3)2

Halite

Gypsum

Limestone

Dolomite

Organic Sedimentary Rock

Coal

– Peat --> Lignite --> Coal– Coal: Bituminous & Anthracite

Bituminous

Anthracite

Organic Sedimentary Rock

Coal• Coal is an organic sedimentary rock that has been altered slightly by being compressed and heated.

• It was formed by the rapid burial of large numbers of plants; swamp forest.

• Over time the plant material is compacted so much by the weight of the overlying sediment that it is turned in to rock.

Organic Sedimentary Rock

Coal• Coal is a nonrenewable energy source because it takes millions of years to create. (mostly formed during the Carboniferous period)

• It is composed primarily of carbon along with variable quantities of other elements, chiefly sulfur, hydrogen, oxygen and nitrogen.

Organic Sedimentary Rock

Organic Sedimentary Rock

Organic Sedimentary Rock

Organic Sedimentary Rock

Organic Sedimentary Rock

Coal

Coal

•Xcel's Cherokee Power Plant near 64th and Washington streets.

•Plant Description: Cherokee Station is a coal-fired, steam-electric generating station with four operating units.

•Fuel Source: Low-sulfur coal supplied by several mines in western Colorado, including Twentymile Mine, ColoWyo Mine, West Elk Mine and Powderhorn Mine.

Sedimentary Environments

• A sedimentary rock can tell you something about what the environment was like when and where the sediment was deposited.

o Lakeso Lower courses of riverso Shallow oceano Deep ocean