Flint, Chert, and Jasper
Chert is a sedimentary rock composed of microcrystallite quartz. It is a tough rock that ancient people used to make tools and weapons. It can be broken to form very sharp edges. It also produces a spark when struck with a piece of metal. Chert (/ ? t? ??r t /) is a hard, fine-grained sedimentary rock composed of microcrystalline (or cryptocrystalline) crystals of quartz, the mineral form of silicon dioxide (SiO 2). Chert is characteristically of biological origin but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood.. Chert is typically composed of the petrified.
Covid has significantly affected our fundraising. Please help! Learning Center What is a mineral? Mineral Name:. Locality Name:. Keyword s :. Chert This page is currently not sponsored. Click here to sponsor this page. Photos of Chert Chert Gallery Search Photos of Chert. Flint Helgoland, Schleswig-Holstein, Germany. Hide all sections Show all sections. This section is currently hidden. Click the show button to view. Colour: Gray, how to view website certificate black, brown and other colors due to staining.
Name: "Chert, perhaps originally chirt, is believed to be a local English term that was taken into geological use. It may be of onomatopoeic origin. The name chert may be of more recent origin than flint, and unlike flint, is not found in literary usage. It was well established in meaning in A dense, hard siliceous-rock how to update to windows 10 low porosity.
Cherts are tough, compact rocks with low porosity that are composed mainly of microcrystalline quartz and varying amounts of impurities Folk et al ; Smith The quartz occurs as randomly interlocked, gock quartz grains microquartz or fibrous chalcedony Folk et al ; Smith ; Oldershaw ; Knauth Cherts occur in a variety of geological settings, roxk example: - Bedded cherts may form by compaction and recrystallization of silica-rich biogenic sediments made of opaline tests of single-cell organisms diatoms, radiolaria or remains of silicious sponges, both in marine ued in lake environments.
During diagenesis, the silica in the sediments undergoes a transformation from opal-A through opal-CT to microcrystalline quartz in the mature chert Oldershaw ; Calvert ; Lancelot ; Hein et al ; Pisciotto ; Riech ; Levitan ; Jones et al ; Compton Accordingly, these cherts may contain some opal-CT.
Silica mobilized from volcaniclastic sediments, hydrothermal solutions whatt clay minerals may contribute to the silicification Calvert ; Thurston ; Pollock ; Hesse They typically form during early diagenesis by precipitation of silica mobilized from biogenic sources like radiolarian tests or sponge spicules.
Buurman et al ; Meyers ; Bustillo et al ; Maliva et al ; Knauth ; Madsen et al The term "chert" is occasionally also used for massive rocks made primarily of microcrystalline rocl that deposits around submarine volcanic rocm vents "black smokers"; Hopkinson et al ; Gutzmer et alor that formed as siliceous sinter, like Rhynie chert Hesse Siliceous precursor rocks of comparable texture that are primarily made of opal-A or opal-CT are sometimes also called chert, but usually with the addition of the dominant silica phase, for example, "opaline chert" e.
Weaver et al ; PisciottoCalvert dhert Cady et al Rock Sedimentary rock and sediment Sedimentary rock Biochemical and chemical sedimentary rock Siliceous-rock Chert. Non-essential minerals - these minerals are common, sometimes major components, but are not always present:. Hornstone Mozarkite. German: Mozarkit Hornstein in part Silex in part. Novaculite Novaculite is a uniform, fine-grained hard rock mostly composed of extremely fine-grained to cryptocrystalline quartz.
It may be white, gray, or black due to impurities. It is not a slate. Ribbonstone A ksed variety of chert. Taconite Taconite also spelled taconyte The cherty or jaspery rock that enclosed the Mesabi iron ores in Minnesota. In a somewhat more general sense, it designates any bedded ferruginous chert of the Lake Superior district.
Associated Minerals Based on Photo Data:. Reference List:. American Journal of Science Smith, W. Geologie en Mijnbouw 39e, Hay, R. Contributions to Mineralogy and Petrology 17, Oldershaw, A. Sedimentology fr, what is chert rock used for Ernst, W. G, Calvert, S. American Journal of Science A, Eugster, H.
Contributions to Mineralogy and Petrology 22, Mizutani, S. Sedimentology 15, Buurman, P. Geologie en Mijnbouw 50, wyat Calvert, S. Contributions to Mineralogy and Petrology 33, Thurston, D. Contributions to Ls and Petrology 36, Lancelot, Y. Meyers, W. Sedimentology 24, Contributions to Mineralogy and Petrology, 61, Hein, J. What size file can i upload to dropbox, Allan, M.
Pisciotto, K. Sedimentology 28, Riech, V. Levitan, M. Laschet, C. Facies 10, Hesse, R. Earth-Science Reviews 26, os Bustillo, M. Sedimentology 34, Maliva, R. Palaios 4, Sedimentology 36, Compton, J. Clay fod Clay Minerals 39, Knauth, L. In: Reviews in Mineralogy, Vol. Cady, S. American Mineralogist 81, Sugitani, K.
Sedimentology 45, Hopkinson, L. Contributions to Mineralogy and Petrology Gutzmer, J. Usedd, T. Mineralium Deposita 38, H, Simonson, B. Cheft Society of America What is chert rock used for Fischer, W. Madsen, H.
Chert; Chert is a fine-grained sedimentary rock composed of quartz (SiO2) that is microcrystalline or cryptocrystalline quartz. It is usually organic rock but also occur inorganically as a chemical precipitate or a diagenetic replacement. It occurs as nodules, concretionary masses, and as layered deposits. Chert and flint, very fine-grained quartz (q.v.), a silica mineral with minor impurities. Several varieties are included under the general term chert: jasper, chalcedony, agate (qq.v.), flint, porcelanite, and novaculite. Flint is gray to black and nearly opaque (translucent brown in thin. The term "chert" is occasionally also used for massive rocks made primarily of microcrystalline quartz that deposits around submarine volcanic hydrothermal vents ("black smokers"; Hopkinson et al ; Gutzmer et al ), or that formed as siliceous sinter, like Rhynie chert (Hesse ).
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth's surface , followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment , and may be composed of geological detritus minerals or biological detritus organic matter.
The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement , which are called agents of denudation. Biological detritus was formed by bodies and parts mainly shells of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies marine snow.
Sedimentation may also occur as dissolved minerals precipitate from water solution. Sedimentary rocks are deposited in layers as strata , forming a structure called bedding.
Sedimentary rocks are often deposited in large structures called sedimentary basins. Sedimentary rocks have also been found on Mars.
The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering , for example in the construction of roads , houses , tunnels , canals or other structures.
Sedimentary rocks are also important sources of natural resources including coal , fossil fuels , drinking water and ores. The study of the sequence of sedimentary rock strata is the main source for an understanding of the Earth's history , including palaeogeography , paleoclimatology and the history of life. The scientific discipline that studies the properties and origin of sedimentary rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences , such as pedology , geomorphology , geochemistry and structural geology.
Sedimentary rocks can be subdivided into four groups based on the processes responsible for their formation: clastic sedimentary rocks, biochemical biogenic sedimentary rocks, chemical sedimentary rocks, and a fourth category for "other" sedimentary rocks formed by impacts, volcanism , and other minor processes.
Clastic sedimentary rocks are composed of rock fragments clasts that have been cemented together. The clasts are commonly individual grains of quartz , feldspar , clay minerals , or mica.
However, any type of mineral may be present. Clasts may also be lithic fragments composed of more than one mineral. Clastic sedimentary rocks are subdivided according to the dominant particle size. The classification of clastic sedimentary rocks parallels this scheme; conglomerates and breccias are made mostly of gravel , sandstones are made mostly of sand , and mudrocks are made mostly of mud.
This tripartite subdivision is mirrored by the broad categories of rudites , arenites , and lutites , respectively, in older literature. The subdivision of these three broad categories is based on differences in clast shape conglomerates and breccias , composition sandstones , or grain size or texture mudrocks. Conglomerates are dominantly composed of rounded gravel , while breccias are composed of dominantly angular gravel.
Sandstone classification schemes vary widely, but most geologists have adopted the Dott scheme,  which uses the relative abundance of quartz, feldspar, and lithic framework grains and the abundance of a muddy matrix between the larger grains.
Six sandstone names are possible using the descriptors for grain composition quartz-, feldspathic-, and lithic- and the amount of matrix wacke or arenite.
Although the Dott classification scheme  is widely used by sedimentologists, common names like greywacke , arkose , and quartz sandstone are still widely used by non-specialists and in popular literature.
These relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension. Most authors presently use the term "mudrock" to refer to all rocks composed dominantly of mud.
Biochemical sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue. Examples include:. Chemical sedimentary rock forms when mineral constituents in solution become supersaturated and inorganically precipitate. Common chemical sedimentary rocks include oolitic limestone and rocks composed of evaporite minerals, such as halite rock salt , sylvite , baryte and gypsum. This fourth miscellaneous category includes volcanic tuff and volcanic breccias formed by deposition and later cementation of lava fragments erupted by volcanoes, and impact breccias formed after impact events.
Steeply dipping sedimentary rock strata along the Chalous Road in northern Iran. Alternatively, sedimentary rocks can be subdivided into compositional groups based on their mineralogy:. Sedimentary rocks are formed when sediment is deposited out of air, ice, wind, gravity, or water flows carrying the particles in suspension.
This sediment is often formed when weathering and erosion break down a rock into loose material in a source area. The material is then transported from the source area to the deposition area. The type of sediment transported depends on the geology of the hinterland the source area of the sediment. However, some sedimentary rocks, such as evaporites , are composed of material that form at the place of deposition.
The nature of a sedimentary rock, therefore, not only depends on the sediment supply, but also on the sedimentary depositional environment in which it formed. As sediments accumulate in a depositional environment, older sediments are buried by younger sediments, and they undergo diagenesis. Diagenesis includes all the chemical, physical, and biological changes, exclusive of surface weathering, undergone by a sediment after its initial deposition. This includes compaction and lithification of the sediments.
Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. Compaction takes place as the sediments come under increasing overburden lithostatic pressure from overlying sediments.
Sediment grains move into more compact arrangements, grains of ductile minerals such as mica are deformed, and pore space is reduced. Sediments are typically saturated with groundwater or seawater when originally deposited, and as pore space is reduced, much of these connate fluids are expelled. In addition to this physical compaction, chemical compaction may take place via pressure solution.
Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact.
Lithification follows closely on compaction, as increased temperatures at depth hasten the precipitation of cement that binds the grains together. Pressure solution contributes to this process of cementation , as the mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. This further reduces porosity and makes the rock more compact and competent. Unroofing of buried sedimentary rock is accompanied by telogenesis , the third and final stage of diagenesis. At sufficiently high temperature and pressure, the realm of diagenesis makes way for metamorphism , the process that forms metamorphic rock.
The color of a sedimentary rock is often mostly determined by iron , an element with two major oxides: iron II oxide and iron III oxide. Iron II oxide FeO only forms under low oxygen anoxic circumstances and gives the rock a grey or greenish colour. Iron III oxide Fe 2 O 3 in a richer oxygen environment is often found in the form of the mineral hematite and gives the rock a reddish to brownish colour.
In arid continental climates rocks are in direct contact with the atmosphere, and oxidation is an important process, giving the rock a red or orange colour. Thick sequences of red sedimentary rocks formed in arid climates are called red beds. However, a red colour does not necessarily mean the rock formed in a continental environment or arid climate. The presence of organic material can colour a rock black or grey. Organic material is formed from dead organisms, mostly plants.
Normally, such material eventually decays by oxidation or bacterial activity. Under anoxic circumstances, however, organic material cannot decay and leaves a dark sediment, rich in organic material. This can, for example, occur at the bottom of deep seas and lakes. There is little water mixing in such environments; as a result, oxygen from surface water is not brought down, and the deposited sediment is normally a fine dark clay.
Dark rocks, rich in organic material, are therefore often shales. The size , form and orientation of clasts the original pieces of rock in a sediment is called its texture. The texture is a small-scale property of a rock, but determines many of its large-scale properties, such as the density , porosity or permeability. The 3D orientation of the clasts is called the fabric of the rock.
The size and form of clasts can be used to determine the velocity and direction of current in the sedimentary environment that moved the clasts from their origin; fine, calcareous mud only settles in quiet water while gravel and larger clasts are moved only by rapidly moving water. The grain size can be expressed as a diameter or a volume, and is always an average value, since a rock is composed of clasts with different sizes.
The statistical distribution of grain sizes is different for different rock types and is described in a property called the sorting of the rock. When all clasts are more or less of the same size, the rock is called 'well-sorted', and when there is a large spread in grain size, the rock is called 'poorly sorted'.
The form of the clasts can reflect the origin of the rock. For example, coquina , a rock composed of clasts of broken shells, can only form in energetic water. The form of a clast can be described by using four parameters:  . Chemical sedimentary rocks have a non-clastic texture, consisting entirely of crystals.
To describe such a texture, only the average size of the crystals and the fabric are necessary. Most sedimentary rocks contain either quartz siliciclastic rocks or calcite carbonate rocks.
In contrast to igneous and metamorphic rocks, a sedimentary rock usually contains very few different major minerals. However, the origin of the minerals in a sedimentary rock is often more complex than in an igneous rock. Minerals in a sedimentary rock may have been present in the original sediments or may formed by precipitation during diagenesis.
In the second case, a mineral precipitate may have grown over an older generation of cement. Carbonate rocks predominantly consist of carbonate minerals such as calcite , aragonite or dolomite. Both the cement and the clasts including fossils and ooids of a carbonate sedimentary rock usually consist of carbonate minerals. The mineralogy of a clastic rock is determined by the material supplied by the source area, the manner of its transport to the place of deposition and the stability of that particular mineral.
The resistance of rock-forming minerals to weathering is expressed by the Goldich dissolution series. In this series, quartz is the most stable, followed by feldspar , micas , and finally other less stable minerals that are only present when little weathering has occurred.
In most sedimentary rocks, mica, feldspar and less stable minerals have been weathered to clay minerals like kaolinite , illite or smectite.
Among the three major types of rock, fossils are most commonly found in sedimentary rock. Unlike most igneous and metamorphic rocks, sedimentary rocks form at temperatures and pressures that do not destroy fossil remnants.
Often these fossils may only be visible under magnification. Dead organisms in nature are usually quickly removed by scavengers , bacteria , rotting and erosion, but under exceptional circumstances, these natural processes are unable to take place, leading to fossilisation.
The chance of fossilisation is higher when the sedimentation rate is high so that a carcass is quickly buried , in anoxic environments where little bacterial activity occurs or when the organism had a particularly hard skeleton.