Limestone is used in many ways. Some of the most common are: production of cement, crushed stone , and acid neutralization. Iron Ore is a chemical sedimentary rock that forms when iron and oxygen and sometimes other substances combine in solution and deposit as a sediment. Hematite shown above is the most common sedimentary iron ore mineral. Rock Salt is a chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters.
It is also known by the mineral name " halite. It is often mined for use in the chemical industry or for use as a winter highway treatment. Some halite is processed for use as a seasoning for food. Oil Shale is a rock that contains significant amounts of organic material in the form of kerogen.
This is usually much less efficient than drilling rocks that will yield oil or gas directly into a well. The processes used for hydrocarbon extraction also produce emissions and waste products that cause significant environmental concerns.
It typically breaks into thin flat pieces. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains, and deltas. The best way to learn about rocks is to have a collection of specimens to examine while you study. Seeing and handling the rocks will help you understand their composition and texture much better than reading about them on a website or in a book.
The Geology. Mineral collections and instructive books are also available. The specimen in the photo is about two inches five centimeters across. Article by: Hobart M. Find Other Topics on Geology. Maps Volcanoes World Maps. Rock, Mineral and Fossil Collections.
Hardness Picks. Flint, Chert, and Jasper. Tumbled Stones. Fluorescent Minerals. Explanation: Erosion breaks down rocks, sedimentary layers, metaphoric rocks and igneous protrusions are all broken down by erosion. Related questions What are sediments and how are they formed?
How are sediments classified? What is an evaporite and how is it formed? How are sedimentary rocks different from igneous and metamorphic rocks? Why do sedimentary rocks have layers? What happens when limestone comes in contact with an acid? Why are sedimentary rocks the only rock type to contain fossils? Why are sedimentary rocks stratified? Why are sedimentary rocks important?
What are some examples of sedimentary rocks that react with acid? Tufa can form near degassing water and in saline lakes. Waterfalls downstream of springs often precipitate tufa as the turbulent water enhances the degassing of carbon dioxide, which makes calcite less soluble and causes it to precipitate. Saline lakes concentrate calcium carbonate from a combination of wave action causing degassing, springs in the lakebed, and evaporation. In salty Mono Lake in California, tufa towers were exposed after water was diverted and lowered the lake levels.
Cave deposits like stalactites and stalagmites are another form of chemical precipitation of calcite, in a form called travertine. Calcite slowly precipitates from water to form the travertine, which often shows banding. This process is similar to the mineral growth on faucets in your home sink or shower that comes from hard mineral-rich water. Oxygenation of the atmosphere and oceans caused free iron ions, which are water-soluble, to become oxidized and precipitate out of solution.
The iron oxide was deposited, usually in bands alternating with layers of chert. Chert , another commonly found chemical sedimentary rock, is usually produced from silica SiO 2 precipitated from groundwater. Silica is highly insoluble on the surface of Earth, which is why quartz is so resistant to chemical weathering.
Water deep underground is subjected to higher pressures and temperatures, which helps dissolve silica into an aqueous solution. As the groundwater rises toward or emerges at the surface the silica precipitates out, often as a cementing agent or into nodules.
For example, the bases of the geysers in Yellowstone National Park are surrounded by silica deposits called geyserite or sinter. The silica is dissolved in water that is thermally heated by a relatively deep magma source.
Chert can also form biochemically and is discussed in the Biochemical subsection. Chert has many synonyms, some of which may have gem value such as jasper, flint, onyx, and agate, due to subtle differences in colors, striping, etc.
Oolites are among the few limestone forms created by an inorganic chemical process, similar to what happens in evaporite deposition. When water is oversaturated with calcite, the mineral precipitates out around a nucleus, a sand grain or shell fragment, and forms little spheres called ooids see figure.
As evaporation continues, the ooids continue building concentric layers of calcite as they roll around in gentle currents. Biochemical sedimentary rocks are not that different from chemical sedimentary rocks; they are also formed from ions dissolved in solution. However, biochemical sedimentary rocks rely on biological processes to extract the dissolved materials out of the water. Most macroscopic marine organisms use dissolved minerals, primarily aragonite calcium carbonate , to build hard parts such as shells.
When organisms die the hard parts settle as sediment, which becomes buried, compacted, and cemented into rock. This biochemical extraction and secretion is the main process for forming limestone , the most commonly occurring, non-clastic sedimentary rock.
Solid calcite reacts with hydrochloric acid by effervescing or fizzing. Dolomite only reacts to hydrochloric acid when ground into a powder, which can be done by scratching the rock surface see Chapter 3 , Minerals. Limestone occurs in many forms, most of which originate from biological processes. Entire coral reefs and their ecosystems can be preserved in exquisite detail in limestone rock see figure.
Fossiliferous limestone contains many visible fossils. A type of limestone called coquina originates from beach sands made predominantly of shells that were then lithified. Coquina is composed of loosely-cemented shells and shell fragments. You can find beaches like this in modern tropical environments, such as the Bahamas. Chalk contains high concentrations of shells from a microorganism called a coccolithophore. Micrite , also known as microscopic calcite mud, is a very fine-grained limestone containing microfossils that can only be seen using a microscope.
Biogenetic chert forms on the deep ocean floor, created from biochemical sediment made of microscopic organic shells. This sediment, called ooze, may be calcareous calcium carbonate-based or siliceous silica-based depending on the type of shells deposited.
For example, the shells of radiolarians zooplankton and diatoms phytoplankton are made of silica, so they produce siliceous ooze.
Under the right conditions, intact pieces of organic material or material derived from organic sources are preserved in the geologic record. Although not derived from sediment, this lithified organic material is associated with sedimentary strata and created by similar processes—burial, compaction, and diagenesis.
Deposits of these fuels develop in areas where organic material collects in large quantities. Lush swamplands can create conditions conducive to the coal formation. Shallow-water, organic material-rich marine sediment can become highly productive petroleum and natural gas deposits. See Chapter 16 , Energy and Mineral Resources, for a more in-depth look at these fossil-derived energy sources.
In contrast to detrital sediment, chemical, biochemical, and organic sedimentary rocks are classified based on mineral composition. Most of these are monomineralic, composed of a single mineral, so the rock name is usually associated with the identifying mineral. Chemical sedimentary rocks consisting of halite are called rock salt. Rocks made of Limestone calcite is an exception, having elaborate subclassifications and even two competing classification methods: Folk Classification and Dunham Classification [ 11 ; 21 ].
The Folk Classification deals with rock grains and usually requires a specialized, petrographic microscope. The Dunham Classification is based on rock texture, which is visible to the naked eye or using a hand lens and is easier for field applications. Most carbonate geologists use the Dunham system. Udden, J. Mechanical composition of clastic sediments.
Wentworth, C. A scale of grade and class terms for clastic sediments. Folk, R. Petrography of sedimentary rocks. Texas, Hemphill, Austin, Tex , Dickinson, W. Interpreting detrital modes of graywacke and arkose. Affolter, M. On the nature of volcanic lithic fragments: Definition source and evolution. Plate tectonics and sandstone compositions.
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