zoocreation


CONCRETIONS




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CONCRETIONS



SAND CRYSTALS AND sand concretions



A number of different sand-included mineral formations (calcite, gypsum, barite, etc.) have traditionally been referred to as concretions. Technically, sand crystals have a regular crystalline growth pattern (not obviously influenced by the sand itself), while sand concretions are round or irregular, but the composition is essentially the same when both occur together (Neutkens, Löffler, and Wilson 2014). Sand crystals are known from different parts of the world, but readily-identifiable crystals come from a handful of locations. The local sand composition determines whether the crystals are fine- or coarse-grained, as well as coloration.



SAND CALCITE



FONTAINEBLEAU, FRANCE



Sand calcites in the Paris Basin formed during the Pleistocene, long after the sand deposition. “Horizontal arrays of sand calcite crystals mark the position of paleo-water tables and are evidence of former hydrologic conditions” (Thiry et al. 2020). The chemical generation of hydrogen carbonate in the presence of calcium from limestone lead to the precipitation of calcium carbonate. As the calcite crystalized, it incorporated sand particles (Neutkens, Löffler, and Wilson 2014). The crystal habit at Fontainebleau suggests formation at a lower temperature than crystals formed at Rattlesnake Butte, South Dakota.



SAND CALCITE



RATTLESNAKE BUTTE, SOUTH DAKOTA



The sand calcite crystals from Rattlesnake Butte are usually rhombohedral, and often found in attractive group clusters. While the Rattlesnake Butte locality is now closed to collecting (though there are plenty of old specimens out there), very similar sand crystal forms are being dug up near Lake Havasu, Arizona. Other sand calcite crystal habits have been recorded from Cholame Hills, California, Goshen Hole, Wyoming, and Garfield Co., Utah (Sargent and Zeller 1984; Huizing and Richards 2021).



SAND CALCITE



Near lake havasu city, Mohave county, arizona



SAND CALCITE



Goshen hole, wyoming



SAND CALCITE



gARFIELD cOUNTY, uTAH



SAND GYPSUM CRYSTALS



jET, oKLAHMOA



GYPSUM ROSE



SAHARA DESERT



Desert roses are evaporites, where a sulphate (gypsum or barite) precipitates from evaporating fluid to form ‘petals’ or ‘rosettes.’ These enclose sand grains, cementing them together as the crystals grow. (Shahid and Abdelfattah (2009) noted some gypsum roses that were relatively pure of sand inclusion.) While these are found in arid regions, desert rose formation requires groundwater beneath the sands. Formation is frequent, each probably completed within tens of years, as exposed desert roses do not last weathering long (Mougenot 2000). A fluctuating water table helps bring a ‘brine’ close to the surface, where evaporation allows the crystals to start forming through precipitation in the spaces between the loosely-packed sand grains (Al-Hussaini et al. 2015).



GYPSUM ROSE



Chihuahua, MEXICO



These desert roses are “spherical aggregates, built up of . . . colorless gypsum plates, and on the edge of the rosettes a white crust of anhydrite . . . is present” (Papp et al. 2012). Sand inclusions are found banded with sand-free zones within the desert rose. Some desert roses are referred to as ‘selenite,’ but that term, according to White (2003), refers specifically to the gypsum variety that is transparent, with distinct crystals or broad folia. Sand-included desert roses would not qualify.



SAND CALCITE



Mályi, Borsod-Abaúj-Zemplén County, Hungary



Huizing and Richards (2021) noted the botryoidal sand calcite formations from this locality could be considered true concretions.


SAND CELESTINE



Mount Ungoza, KAZAKHSTAN



This is the primary (only?) locality with sand-included celestine crystals.



BARITE ROSE



OKLAHOMA



The barite rose is the official state rock of Oklahoma, though technically it is a mineral (London 2008). Barite is the ‘cementing’ agent, incorporating quartz sand grains. It can form nodular concretions or rosettes, and may include disc or radial blade growth (Tarr 1933; London 2008). Similar barite roses are known from Kansas (Knerr 1897-1898) and a few other localities around the world. The Oklahoma barite roses are found in the Garber Sandstone. London (2008) noted that they “could have formed in a single event, episodically, or continuously since the end of the Permian, and they may still be forming today.”



SAND SPIKE



MT. SIGNAL, IMPERIAL COUNTY, CALIFORNIA



Sand spikes are formed from a botryoidal ball concretion from which a tapering stem projects. Best known from the Imperial Valley near Mt. Signal (Garner 1936), similar spikes have been found in Germany (Buchner, Sach, and Schmieder 2021).



SAND SPIKE



MT. SIGNAL, IMPERIAL COUNTY, CALIFORNIA



Particularly of interest at the Mt. Signal location was that, “Regardless of size or minor structural details all specimens of the mace-like or club type were found to lie with their ‘heads’ to the South and toward the primary beds, while their tail-like stems of course pointed to the North” (Garner 1936). While it was originally thought that water flow was responsible for their orientation, recent research shows that these may be seismites, formed during an earthquake. Seismic waves ‘dewater’ the sediment, with compacted sand bodies being cemented into spike-like forms by available carbonate in the sediment. The ‘tails’ grow in the direction away from the seismic source (Buchner, Sach, and Schmieder 2021).



FAIRY sTONES



These calcium carbonate concretions are known by different names around the world, including marlekor or imatra stones.



FAIRY STONE



hARRICANA rIVER, qUEBEC, cANADA



FAIRY STONE



hARRICANA rIVER, qUEBEC, cANADA



FAIRY STONE



hARRICANA rIVER, qUEBEC, cANADA



FAIRY STONE



hARRICANA rIVER, qUEBEC, cANADA



FAIRY STONE



hARRICANA rIVER, qUEBEC, cANADA



DROPSTONE CARRIED BY GLACIER



JAMES BAY ROAD, QUEBEC, CANADA



claystone concretion





Sharon, Vermont



claystone concretion





'The Salamander,'

Sharon, Vermont



PSEUDOFOSSILS AND PSEUDOMORPHS



Pseudofossils are natural rock or mineral formations and structures that resemble fossils, but have no relationship to actual fossilized organisms. The cracks in rough septarian stones have fooled some people into thinking they were fossil turtles, for example (Monroe and Dietrich 1990). A pseudomorph is a mineral that replaces another mineral, taking on the original mineral's form (which usually isn't part of the second mineral's habit).



GLENDONITE



Taimyr Peninsula, Krasnoyarsk, Siberia



Glendonites are calcite pseudomorphs after ikaite. The crystals often form within the core of mudstone concretions (Boggs, Jr. 1975; Selleck et al. 2007), which themselves form from decomposition of organic matter. The decomposing matter serves as a carbon source for both concretion and ikaite crystals (Muramiya et al. 2022). The crystals form rapidly at the same time as the concretion (Muramiya et al. 2022; Vasileva et al. 2020).



GLENDONITE



KOLA PENINSULA, RUSSIA



Ikaite forms in water of near-freezing temperature, and rapidly decomposes to calcite when the water warms to temperatures above 4°C (Selleck et al. 2007). It can develop into tufa, also (Bischoff et al. 1993). These low temperatures have implications for exploring paleoenvironments, so glendonites are of interest to those researchers (De Lurio and Frakes 1999), though there are some issues that need to be addressed (Vickers et al. 2018).



GOETHITE AFTER PYRITE / MARCASITE



WHITE SANDS DESERT, EGYPT



These mineral aggregates are found in many different forms (stellate, as above, as well as cuboid, tubular, spherical, etc.). Allen, Bailey, and Tewksbury (2014) determined these aggregates are primarily goethite, having replaced either pyrite or marcasite, depending on the specimen.



KERKOUB



MOROCCO



Soleilhavoup (2011) noted that kerkoubs are sandstone concretions found in the north and central Sahara, and in Jordan. The grain may be fine or coarse depending on the host sandstone. These are sometimes mistaken as stromatolites, but are probably the result of colonial calcifying bacteria, possibly formed during the last ‘wet phase’ of the Sahara.



GOETHITE PSEUDO-STROMATOLITE



MOROCCO



Goethite concretions form in the North African desert as dissolved iron in the water precipitates, sometimes in concentric patterns. Erosion by water and wind wears away the softer host material. These concretions are sometimes mistakenly identified as stromatolites because of the banding pattern.



GOETHITE PSEUDO-STROMATOLITE



MOROCCO



The color difference comes from 'desert varnish,' that produces a darker, shiny coloration. Desert varnish is a coating of silica layers that are deposited over time, turning black through concentration of manganese (Perry and Sephton 2008). These layers can trap other trace elements and biological material.



Dinocochlea ingens





Dinocochlea was first thought the be the shell of a giant gastropod (Woodward 1922; images left), later a possible coprolite or trace fossil. Taylor and Sendino (2011) proposed that it was a concretion that grew around a slender helical burrow. Similar helical concretions have been discovered in Alaska (Locock et al. 2020), accompanied by spheroidal and botryoidal concretions.



PEARLS AND similar BIOLOGICAL CONCRETIONS



Kidney stones are also concretions, but pearls are more interesting.



PEARL



TAHITI (CULTIVATED)



Natural pearls form when, after an irritation, the oyster (or other mollusk) first produces horny skin (periostracum), then secretes calcium carbonate (columnar calcite), forming a concretion. After some time, tabular aragonite (nacre) is precipitated (Hanni 1995). This nacre, as added layers become more ordered with smaller crystals, adds lustre and fracture resistance (Liu et al. 2012). In cultured pearls, nucleation may begin with beads or mantle tissue.



QUEEN CONCH PEARL



(Credit: Florida Atlantic University, Harbor Branch Oceanographic Institute)



Other mollusks can produce non-nacreous pearls, including scallops (Scarratt and Hanni 2004), quahog clams (Ho 2015), pen shells (Sturman et al. 2014), and gastropods (Hainschwang et al. 2010). The Caribbean’s queen conch (Strombus gigas) produces pearls in a variety of colors, but is best known for pink pearls. The coloration of pink conch pearls is not stable (likely originating in organic carotenoid pigments) and can fade with prolonged exposure to sunlight (Dexter 1954; Fritsch and Miosiorowski 1987). Melo sea snails of southeast Asian waters can produce an attractive yellow to orange pearl (Pardieu 2009). Some crustaceans have produced non-nacreous calcareous concretions (Tirmizi and Kazmi 1990), and they may turn up as growths in other organisms also.



CONE-IN-CONE



Cone-in-cone calcite is a type of “fibrous diagenetic” calcite (Kershaw and Guo 2016). Gypsum and quartz can also form fibrous cements, and siderite and pyrite cones have been found (Sellés-Martinez 1994). Cone-in-cone formations are nested masses of crystals that look like stacked cones. They can be found around the world in a wide stratigraphic range, and have been found in both marine and non-marine sediments (Kershaw and Guo 2016). They are mostly found in “horizontal veins or layers and also in calcitic rims of concretions in shales or sandy shales” (Selles-Martinez 1994).



CONE-IN-CONE



LAKE KANOPOLIS, kansas



Aso et al. (1992) noted that several forms of cone-in-cone have been described based on fiber arrangement: feather-like, with fibers diverging independently from the axis; arborescent, with fibers diverging independently but bilateral symmetry; card house, with cones showing bilateral symmetry and parallel axis, and structural connections between fibers.



CONE-IN-CONE



LAKE KANOPOLIS, kansas



The direct relationship between cone-in-cone formations and concretions varies depending on how they may have formed. Hesse et al. (2019) noted that while there are many hypotheses of formation, they can be grouped generally as “those assuming early displacive formation of concretions in soft, unconsolidated sediment, and those that emphasize late fracturing of concretions with or without excess pore fluid.”



CONE-IN-CONE



ELK CREEK, ERIE COUNTY, PENNSYLVANIA



One paper by early researchers suggested that, at least in some cases, cone-in-cone started out as an aragonite concretion that recrystallized into calcite, with the cone structures developing under various internal and external pressures (Gilman and Metzger 1967).



CONE-IN-CONE



ELK CREEK, ERIE COUNTY, PENNSYLVANIA



Lyle et al. (2008) suggested that cone-in-cone formations are the result of “precipitation and growth of fibrous crystals of calcite soon after sediments were deposited,” before the sediment had firmed, with organic matter lowering the pH to cause the calcite to recrystallize, and compaction directing the near-vertical orientation.



CONE-IN-CONE



ELK CREEK, ERIE COUNTY, PENNSYLVANIA



Meinhold et al. (2019) stated, “CIC calcite forms by precipitation, mainly from supersaturated aqueous solutions, as a result of chemical reactions, or changes in physical conditions, especially temperature and pressure, in bedding parallel fractures that formed by fluid overpressure or by force of crystallization. . . . CIC in general does not form over multiple stages and mineral aggregates composing the structure precipitate with their conical form displacing host sediment.”



CONE-IN-CONE



breathitt formation, perry county, kentucky



CONE-IN-CONE



breathitt formation, perry county, kentucky



CONE-IN-CONE



breathitt formation, perry county, kentucky



CONCRETIONS on Mars



Planetary scientists also study concretions on Earth, to learn more about those found on Mars.



CONCRETIONS ON MARS NEAR FRAM CRATER



(Credit: NASA / JPL-Caltech / Cornell / USGS)



Iron oxide concretions on Earth are often examined as possible analogues for concretions found on Mars.



CONCRETIONS ON MARS AT CUMBERLAND



(Credit: NASA / JPL-Caltech / MSSS)



Concretions on Mars includes ‘blueberry’ spherules and less-densely cemented ‘popcorn’ concretions (Chan et al. 2005).



"BERRIES" ON MARS AT MERIDIANI PLANUM



(Credit: NASA / JPL / Cornell / USGS)



Chan et al. (2005) suggested that Mars concretions “may have formed from mixing of an aqueous fluid that contained iron in solution and a separate oxidizing groundwater that precipitated hematite.” Yoshida et al. (2018) noted the possibility of initial carbonate concretion formation within a warm, wet, dense atmosphere, followed by interaction with acid sulfate water.



concretions or not?



Not every round stone is a concretion, and other geological formations can end up confusing the issue. (And of course, concretions have often been mistaken for other geological specimens, like fossil eggs.)



EGG STONE (NATIVE AMERICAN ARTIFACT)



Midwest



This is a quartzite egg stone, which may have been used as the weight in a cudgel.



VOLCANIC EJECTA



MOJAVE DESERT



Volcanic ejecta tumbled over the desert, coating itself with sand.



KEOKUK GEODE



HAMILTON, ILLINOIS



A geode is "a discrete mass . . . [consisting] of a relatively thin siliceous (commonly dense chalcedony) or calcareous shell and inward-projecting crystals of one or more minerals that partially or completely fill its shell” (Dietrich 2010). Igneous geodes form through mineral deposition in voids that were originally created by gas bubbles in lava or magma, while the origin of sedimentary geodes has been the subject of debate.



GEODE



BLOOMINGTON, INDIANA



Historical speculation about sedimentary geodes suggested that calcareous concretions were internally dissolved, leaving voids that could be filled by minerals (Van Tuyl 1916; Hayes 1964). Today, however, research suggests that anhydrite nodules were the first step in geode formation (Maliva 1987; Smith 2007). Anhydrite can be concretionary, but these nodules weren’t necessarily so.



GEODE



MOROCCO



Some of the internal crystallization in this geode is stalagtitic, which is concretionary.



AGATE NODULE



HEBEI PROVINCE, CHINA



Not all mineral concentration is concretionary, such as with this siliceous (agate) nodule.



MUDBALL



CACHE CREEK, OKLAHOMA



Mudballs are neither concretions or geodes. They are accretionary (Garner 1908), forming “clot-like masses” from sediment suspended in the water (Siemers et al. 2000), or are molded by currents from chunks of mud or clay along lakes, creeks, or marine beaches (Bell 1940; Tanner 1996).



MUDBALL, POLISHED FACE



CACHE CREEK, OKLAHOMA



Additional minerals like calcite may precipitate within the mudball. A particularly interesting form, the armored mudball, will accumulate pebbles on its exterior as it rolls down a stream, bank, or beach (Tanner 1996).



SERPENT MOUND IMPACT EVENT SHATTER CONE



ADAMS COUNTY, OHIO



Cone-in-cone concretions are sometimes mistaken for shatter cones (Lugli et al. 2005). Shatter cones are a “fracture phenomenon” associated with shock metamorphism (Baratoux and Reimold 2016).



SERPENT MOUND IMPACT EVENT SHATTER CONE



ADAMS COUNTY, OHIO



2021-2025





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