Concretions on Bowling Ball Beach (Mendocino County, California) weathered out of steeply tilted Cenozoic mudstone. Concretions in Torysh, Western Kazakhstan.  Concretions with lens shape from island in Vltava river, Prague, Czech Republic. Marlstone aggregate concretion, Sault Ste. Marie, Michigan.  A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin "(act of) compacting, condensing, congealing, uniting", itself from con meaning 'together' and crescere meaning "to grow". Concretions form within layers of sedimentary strata that have already been deposited. They usually form early in the burial history of the sediment, before the rest of the sediment is hardened into rock. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum. Occurrence A mosaic of images showing spherules, some partly embedded, spread over (smaller) soil grains on the Martian surface.  Septarian concretions  upA slice of a typical carbonate-rich septarian nodule. Septarian concretions (or septarian nodules) are carbonate-rich concretions containing angular cavities or cracks (septaria; , from the Latin "partition, separating element", referring to the cracks / cavities separating polygonal blocks of hardened materials). Cracks are highly variable in shape and volume, as well as the degree of shrinkage they indicate. Although it has commonly been assumed that concretions grew incrementally from the inside outwards, the fact that radially oriented cracks taper towards the margins of septarian concretions is taken as evidence that in these cases the periphery was stiffer while the inside was softer, presumably due to a gradient in the amount of CaCO3 precipitate progressively cementing the mud porosity from outside to inside. Moeraki Boulders, New Zealand. A spectacular example of boulder septarian concretions, which are as much as in diameter, are the Moeraki Boulders. These concretions are found eroding out of Paleocene mudstone of the Moeraki Formation exposed along the coast near Moeraki, South Island, New Zealand. They are composed of calcite-cemented mud with septarian veins of calcite and rare late-stage quartz and ferrous dolomite.Boles, J. R., C. A. Landis, and P. Dale, 1985, The Moeraki Boulders; anatomy of some septarian concretions, Journal of Sedimentary Petrology, vol. 55, n. 3, p. 398-406.Fordyce, E., and P. Maxwell, 2003, Canterbury Basin Paleontology and Stratigraphy, Geological Society of New Zealand Annual Field Conference 2003 Field Trip 8, Miscellaneous Publication 116B, Geological Society of New Zealand, Dunedin, New Zealand. Forsyth, P.J., and G. Coates, 1992, The Moeraki boulders. Institute of Geological & Nuclear Sciences, Information Series no. 1, (Lower Hutt, New Zealand)Thyne, G.D., and J.R. Boles, 1989, Isotopic evidence for origin of the Moeraki septarian concretions, New Zealand, Journal of Sedimentary Petrology. v. 59, n. 2, p. 272-279. The much smaller septarian concretions found in the Kimmeridge Clay exposed in cliffs along the Wessex coast of England are more typical examples of septarian concretions. Hiatus concretions upA model of Dinocochlea with Natural History Museum research scientist Paul Taylor as a scale. Hiatus concretions at the base of the Menuha Formation (Upper Cretaceous), the Negev, southern Israel. Hiatus concretion encrusted by bryozoans (thin, branching forms) and an edrioasteroid; Kope Formation (Upper Ordovician), northern Kentucky. Hiatus concretions  are distinguished by their stratigraphic history of exhumation, exposure and reburial. They are found where submarine erosion has concentrated early diagenetic concretions as lag surfaces by washing away surrounding fine-grained sediments. Their significance for stratigraphy, sedimentology and paleontology was first noted by Voigt who referred to them as Hiatus-Konkretionen.Voigt, E., 1968, Uber-Hiatus-Konkretion (dargestellt an Beispielen aus dem Lias): Geologische Rundschau. v. 58, pp. 281–296 "Hiatus" refers to the break in sedimentation that allowed this erosion and exposure. They are found throughout the fossil record but are most common during periods in which calcite sea conditions prevailed, such as the Ordovician, Jurassic and Cretaceous.Zaton, M., 2010, Hiatus concretions: Geology Today. v. 26, pp. 186–189. Most are formed from the cemented infillings of burrow systems in siliciclastic or carbonate sediments. Moqui Marbles Moqui Marbles, hematite, goethite concretions, from the Navajo Sandstone of southeast Utah. The "W" cube at the top is one cubic centimeter in size.  Moqui Marbles, also called Moqui balls or "Moki marbles", are iron oxide concretions which can be found eroding in great abundance out of outcrops of the Navajo Sandstone within south-central and southeastern Utah. These concretions range in shape from spheres to discs, buttons, spiked balls, cylindrical forms, and other odd shapes. They range from pea-size to baseball-size. They were created by the precipitation of iron, which was dissolved in groundwater.Chan, M.A. and W.T. Parry, 2002, 'Mysteries of Sandstone Colors and Concretions in Colorado Plateau Canyon Country PDF version, 468 KB : Utah Geological Survey Public Information Series. n. 77, pp. 1–19.Chan, M.A., B.B. Beitler, W.T. Parry, J. Ormo, and G. Komatsu, 2005. Red Rock and Red Planet Diagenesis: Comparison of Earth and Mars Concretions PDF version, 3.4 MB : GSA Today, v. 15, n. 8, pp. 4–10.Loope D.B., Kettler R.M., Weber K.A., 2011, Morphologic Clues to the origin of Iron Oxide-Cemented Sphereoids, Boxworks, and Pipelike Concretions, Navajo Sandstone of South-Central Utah, U.S.A, The Journal of Geology, Vol. 119, No. 5 (September 2011), pp. 505–520 Claystones, clay dogs, and fairy stones Disc concretions composed of calcium carbonate are often found eroding out of exposures of interlaminated silt and clay, varved, proglacial lake deposits. For example, great numbers of strikingly symmetrical concretions have been found eroding out of outcrops of Quaternary proglacial lake sediments along and in the gravels of the Connecticut River and its tributaries in Massachusetts and Vermont. Depending the specific source of these concretions, they vary in an infinite variety of forms that include disc-shapes; crescent-shapes; watch-shapes; cylindrical or club-shapes; botryoidal masses; and animal-like forms. They can vary in length from to over and often exhibit concentric grooves on their surfaces. In the Connecticut River Valley, these concretions are often called "claystones" because the concretions are harder than the clay enclosing them. In local brickyards, they were called "clay-dogs" either because of their animal-like forms or the concretions were nuisances in molding bricks.Gratacap, L.P., 1884. Opinions Upon Clay Stones and Concretions. The American Naturalist, 18(9), pp.882-892.Sheldon, J.M.A., 1900. Concretions from the Champlain clays of the Connecticut Valley. University Press, Boston. pp.74.Tarr, W.A., 1935. Concretions in the Champlain formation of the Connecticut River Valley. Bulletin of the Geological Society of America, 46(10), pp.1493-1534. Similar disc-shaped calcium carbonate concretions have also been found in the Harricana River valley in the Abitibi-Témiscamingue administrative region of Quebec, and in Östergötland county, Sweden. In Scandinavia, they are known as "marlekor" ("fairy stones").Kindle, E.M., 1923. Range and distribution of certain types of Canadian Pleistocene concretions. Bulletin of the Geological Society of America, 34(3), pp.609-648.Warkentin, B.P., 1967. Carbonate content of concretions in varved sediments. Canadian Journal of Earth Sciences, 4(2), pp.333-333.  
Concretions on Bowling Ball Beach (Mendocino County, California) weathered out of steeply tilted Cenozoic mudstone. Concretions in Torysh, Western Kazakhstan. |left Concretions with lens shape from island in Vltava river, Prague, Czech Republic. Marlstone aggregate concretion, Sault Ste. Marie, Michigan. |left A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin "(act of) compacting, condensing, congealing, uniting", itself from con meaning 'together' and crescere meaning "to grow". Concretions form within layers of sedimentary strata that have already been deposited. They usually form early in the burial history of the sediment, before the rest of the sediment is hardened into rock. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum. Occurrence A mosaic of images showing spherules, some partly embedded, spread over (smaller) soil grains on the Martian surface. |left Septarian concretions Moeraki Boulders, New Zealand. upA slice of a typical carbonate-rich septarian nodule. Septarian concretions (or septarian nodules) are carbonate-rich concretions containing angular cavities or cracks (septaria; , from the Latin "partition, separating element", referring to the cracks / cavities separating polygonal blocks of hardened materials). Cracks are highly variable in shape and volume, as well as the degree of shrinkage they indicate. Although it has commonly been assumed that concretions grew incrementally from the inside outwards, the fact that radially oriented cracks taper towards the margins of septarian concretions is taken as evidence that in these cases the periphery was stiffer while the inside was softer, presumably due to a gradient in the amount of CaCO3 precipitate progressively cementing the mud porosity from outside to inside. A spectacular example of boulder septarian concretions, which are as much as in diameter, are the Moeraki Boulders. These concretions are found eroding out of Paleocene mudstone of the Moeraki Formation exposed along the coast near Moeraki, South Island, New Zealand. They are composed of calcite-cemented mud with septarian veins of calcite and rare late-stage quartz and ferrous dolomite.Boles, J. R., C. A. Landis, and P. Dale, 1985, The Moeraki Boulders; anatomy of some septarian concretions, Journal of Sedimentary Petrology, vol. 55, n. 3, p. 398-406.Fordyce, E., and P. Maxwell, 2003, Canterbury Basin Paleontology and Stratigraphy, Geological Society of New Zealand Annual Field Conference 2003 Field Trip 8, Miscellaneous Publication 116B, Geological Society of New Zealand, Dunedin, New Zealand. Forsyth, P.J., and G. Coates, 1992, The Moeraki boulders. Institute of Geological & Nuclear Sciences, Information Series no. 1, (Lower Hutt, New Zealand)Thyne, G.D., and J.R. Boles, 1989, Isotopic evidence for origin of the Moeraki septarian concretions, New Zealand, Journal of Sedimentary Petrology. v. 59, n. 2, p. 272-279. The much smaller septarian concretions found in the Kimmeridge Clay exposed in cliffs along the Wessex coast of England are more typical examples of septarian concretions. Hiatus concretions Hiatus concretion encrusted by bryozoans (thin, branching forms) and an edrioasteroid; Kope Formation (Upper Ordovician), northern Kentucky. Hiatus concretions at the base of the Menuha Formation (Upper Cretaceous), the Negev, southern Israel.|left Hiatus concretions are distinguished by their stratigraphic history of exhumation, exposure and reburial. They are found where submarine erosion has concentrated early diagenetic concretions as lag surfaces by washing away surrounding fine-grained sediments. Their significance for stratigraphy, sedimentology and paleontology was first noted by Voigt who referred to them as Hiatus-Konkretionen.Voigt, E., 1968, Uber-Hiatus-Konkretion (dargestellt an Beispielen aus dem Lias): Geologische Rundschau. v. 58, pp. 281–296 "Hiatus" refers to the break in sedimentation that allowed this erosion and exposure. They are found throughout the fossil record but are most common during periods in which calcite sea conditions prevailed, such as the Ordovician, Jurassic and Cretaceous.Zaton, M., 2010, Hiatus concretions: Geology Today. v. 26, pp. 186–189. Most are formed from the cemented infillings of burrow systems in siliciclastic or carbonate sediments. Moqui Marbles Moqui Marbles, hematite, goethite concretions, from the Navajo Sandstone of southeast Utah. The "W" cube at the top is one cubic centimeter in size. |left Moqui Marbles, also called Moqui balls or "Moki marbles", are iron oxide concretions which can be found eroding in great abundance out of outcrops of the Navajo Sandstone within south-central and southeastern Utah. These concretions range in shape from spheres to discs, buttons, spiked balls, cylindrical forms, and other odd shapes. They range from pea-size to baseball-size. They were created by the precipitation of iron, which was dissolved in groundwater.Chan, M.A. and W.T. Parry, 2002, 'Mysteries of Sandstone Colors and Concretions in Colorado Plateau Canyon Country PDF version, 468 KB : Utah Geological Survey Public Information Series. n. 77, pp. 1–19.Chan, M.A., B.B. Beitler, W.T. Parry, J. Ormo, and G. Komatsu, 2005. Red Rock and Red Planet Diagenesis: Comparison of Earth and Mars Concretions PDF version, 3.4 MB : GSA Today, v. 15, n. 8, pp. 4–10.Loope D.B., Kettler R.M., Weber K.A., 2011, Morphologic Clues to the origin of Iron Oxide-Cemented Sphereoids, Boxworks, and Pipelike Concretions, Navajo Sandstone of South-Central Utah, U.S.A, The Journal of Geology, Vol. 119, No. 5 (September 2011), pp. 505–520 Claystones, clay dogs, and fairy stones Disc concretions composed of calcium carbonate are often found eroding out of exposures of interlaminated silt and clay, varved, proglacial lake deposits. For example, great numbers of strikingly symmetrical concretions have been found eroding out of outcrops of Quaternary proglacial lake sediments along and in the gravels of the Connecticut River and its tributaries in Massachusetts and Vermont. Depending the specific source of these concretions, they vary in an infinite variety of forms that include disc-shapes; crescent-shapes; watch-shapes; cylindrical or club-shapes; botryoidal masses; and animal-like forms. They can vary in length from to over and often exhibit concentric grooves on their surfaces. In the Connecticut River Valley, these concretions are often called "claystones" because the concretions are harder than the clay enclosing them. In local brickyards, they were called "clay-dogs" either because of their animal-like forms or the concretions were nuisances in molding bricks.Gratacap, L.P., 1884. Opinions Upon Clay Stones and Concretions. The American Naturalist, 18(9), pp.882-892.Sheldon, J.M.A., 1900. Concretions from the Champlain clays of the Connecticut Valley. University Press, Boston. pp.74.Tarr, W.A., 1935. Concretions in the Champlain formation of the Connecticut River Valley. Bulletin of the Geological Society of America, 46(10), pp.1493-1534. Similar disc-shaped calcium carbonate concretions have also been found in the Harricana River valley in the Abitibi-Témiscamingue administrative region of Quebec, and in Östergötland county, Sweden. In Scandinavia, they are known as "marlekor" ("fairy stones").Kindle, E.M., 1923. Range and distribution of certain types of Canadian Pleistocene concretions. Bulletin of the Geological Society of America, 34(3), pp.609-648.Warkentin, B.P., 1967. Carbonate content of concretions in varved sediments. Canadian Journal of Earth Sciences, 4(2), pp.333-333. Gogotte Gogotte concretion Goggottes are sandstone concretions found in Oligocene (~30 million years) aged sediments near Fontainebleau, France. Gogottes have fetced high prices at auction due to their sculpture-like quality.
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Moeraki Boulders, New Zealand.
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Moeraki Boulders, New Zealand.
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upA model of Dinocochlea with Natural History Museum research scientist Paul Taylor as a scale. Hiatus concretions at the base of the Menuha Formation (Upper Cretaceous), the Negev, southern Israel. Hiatus
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at the base of the Menuha Formation (Upper Cretaceous), the Negev, southern Israel.|left Hiatus concretions
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Gogotte Gogotte concretion
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Goggottes are sandstone concretions found in Oligocene (~30 million years) aged sediments near Fontainebleau, France. Gogottes have fetced high prices at auction due to their sculpture-like quality.