Concretion

Clay concretion from road cut, Sharon VT.

© 2019 Jonelle DeFelice

Large orange-colored carbonate sphere, known as concretion, weathered out of the Devonian-age Ohio Shale. Ohio Shale concretions are composed primarily of carbonate (limestone or dolomite) rock and are enclosed within a dark-gray to black shale. The cores of larger concretions are typically calcite, which may surround an arthrodire fish bone or a ...

© Johan Maertens

Fossil wood fragments. Large orange-colored carbonate sphere, known as concretion, weathered out of the Devonian-age Ohio Shale. Ohio Shale concretions are composed primarily of carbonate (limestone or dolomite) rock and are enclosed within a dark-gray to black shale. The cores of larger concretions are typically calcite, which may surround an ...

© Johan Maertens

Collected by Steve Harapiak 1960's-70's.

© Craig Wilson

Septarian concretion (cut to reveal the internal cracks). Bought from Helge Grolig at a mineral show. Found by Dorothea and Helge Grolig in 1986. Collection and photo Erwin Löffler.

© Erwin Löffler

Two cut and polished septarian nodules. Diameter estimated. (Two pale yellow 'Lösskindl' concretions from a different locality in the foreground.) Collection Brunner, photo Erwin Löffler.

© Erwin Löffler

This clay concretion was in a collection we purchased and the information was it came from the shore along the lake, east of Ashland. Rolf Luetcke specimen and photo.

Broken concretion which consist mainly of calcite.

© Martin Reich

Large orange-colored carbonate sphere, known as concretion, weathered out of the Devonian-age Ohio Shale. Ohio Shale concretions are composed primarily of carbonate (limestone or dolomite) rock and are enclosed within a dark-gray to black shale. The cores of larger concretions are typically calcite, which may surround an arthrodire fish bone or a ...

© Johan Maertens

Rounded clay concretion found along the shore east of the town of Ashland. Rolf Luetcke specimen and photo.

Carbonate concretion. Gift from Martin Reich who found it in 2009. Collection and photo Erwin Löffler.

© Erwin Löffler

Collected by Steve Harapiak 1960's-70's.

© Craig Wilson

Group of four cross-sections of apparently cylindrical concretions, each containing longitudinal, radially-oriented veins of quartz uniformly 2-4 mm thick that extend beyond the edges of the concretions, possibly to the surface of a less competent outer layer has since weathered away. The circular portion of the largest piece (upper left) is 25 ...

© 2025 E. L. Clopton

A weathered carbonate concretion in sandstone, with a remnant limonitic rim. Some tafoni also visible.

© R. Bottrill

Concretion, found in 2006. Such concretions were found in the central part of the northern quarry wall. They reached, in rare cases, head-sized dimensions. Collection and photo Erwin Löffler.

© Erwin Löffler

This is a cabinet specimen of a concretion from Mexico. This specimen was in the former collection of Ben B. Chomiak (1924-1958). Ben Chomiak worked for the American Smelting and Refining Corporation (ASARCO) between 1952-1953; the Tsumeb Corporation Ltd. From 1954 until 1955; and ASARCO from 1956 until his death in 1958. While in Mexico he worked ...

© Jamison K. Brizendine

Gray flint in white chalk. From spoils at Dyke Park dredged up from Stamford Harbor.

© 2020 Harold Moritz

Flint nodules within carbonate host rock. Ingrid Palfrader collection.

"Helgoländer Feuerstein" or "roter Feuerstein" (Helgoland flint or red flint) is found at the shores of the small island of Helgoland in the North Sea. The "ideal" Helgoland flint has a red core in black flint surrounded by a white cortex and is high in demand, as it is used by the locals for lapidary works. It was already exported from the ...

© Amir Akhavan

A ball-shaped fossil, the skeleton of a sea urchin (possibly Galerites sp.), inside a gray flint nodule. The skeleton's interior was not completely filled with silica, so a botryoidal layer of blue-gray chalcedony could form and later be overgrown by small sparkling quartz crystals. I found this specimen lying in the sand at the Weissenhäuser ...

© Amir Akhavan

A fossilized sea urchin (Echinocorys scutatus) partially penetrated by irregular flint nodules. The creme-colored test of the fossil is still made of calcite. This is a very clear indication of the concretionary nature of this flint. The specimen (with the locality Dalbyover on the label) very likely comes from a quarry in Cretacean chalk, south ...

© Amir Akhavan

Dimensions: 3" x 1.5" x 1" (left) and 3.5" x 2" x 1" (right). Child photo, closeup of shell imprint, field of view 1/2" across. Two blobby menilite opal concretions. Both are opaque, off-white. The "whale" shaped specimen has a glossy surface, the other more matte. Small shell imprints are scattered on the surface as shown in the close-up ...

Bottle shaped flint concretion, self collected in 2013. Gerard van der Veldt collection and photo.

© Gerard van der Veldt

Cast of very late cretaceous (just before K-T boundary) animal burrow.

© RussRizzo & CAL NEVA MINERAL COMPANY

Dark brown-gray flint with white coating. From spoils at Dyke Park dredged up from Stamford Harbor. Full-res image.

© 2020 Harold Moritz

Part of a tubular flint nodule picked up at a pebble beach of the Baltic Sea near Dänisch Nienhof, Schwedeneck, Schleswig Holstein. Such nodules weather out of Cretacean chalk rocks and have accumulated on beaches along the southern shores of the Baltic Sea. The thick white crust is made of fine-grained quartz, the dense and homogeneously colored ...

© Amir Akhavan

An attractive slab of flint, showing the internal patterns. One side is polished. Size: 15.0 x 8.5 x 0.7 cm. Ex Wolfgang E. Henkel collection.

© Weinrich Minerals, Inc.

3cm "barbapappa with a fossile heart" ;) Found by me in sep.2008 Photo by Tim Welting nov.2008

© Frank de Wit

Nodule of Flint from Cromer, Norfolk in the United Kingdom, showing glassy dark grey (almost black) interior, and some of the lighter-coloured rougher exterior.

© TRG Collection

polished Slice

© Marcus V.

Typical flint nodule from the white (chalk) cliffs at Dover, Kent, England. In this view the nodule is about 7 cm in width. University of Southern Indiana specimen photographed by Norman King.

© Norman King

Broken flint nodule. In 2002 we went to the Cap Blanc Nez to find some fossils and pyrite/marcasite but the beach was covered with sand and found nothing. Bored, we seat down near Strouanne in the flint pebbles and started inspecting them. We recovered this specimen with a fossil shark tooth inbedded in it as well as a few sea urchins turned in ...

© Collection and Copyright (c) 2012, Paul De Bondt

Polished section of flint, measuring 15 x 8 cm. Photo and collection: Gf. Capolupi

© Gf. Capolupi

Flint from this region was used extensively for making all kinds types of tools in Neolithic times. Southern Netherlands Limburg and northeastern Belgian Limburg became one of the most important flint mining sites of Europe, traces of prehistoric mining (3950 - 2650 B.C) can be found near Ryckholt, St.Geertruid (Savelsbos), Valkenburg and Voeren. ...

A cross section of a roughly cylindrical flint nodule that weathered out of marl. Numerous sand grains are embedded in the flint matrix, evidence that the calcite in the marl has been metasomatically replaced by chalcedony during diagenesis.

© Amir Akhavan

Sílex. Nódulo bandeado. 5 x 4 cm. Col. Rafa Muñoz, foto Honorio Cócera

© Rafa Muñoz Alvarado

This piece of dark grey flint with yellow-white cortex, contains small fossil remains such as Echinodermata (spiny-skinned animals like starfish, sea urchins, sea cucumbers, sand dollars etc.) The white spines of the calcareous exoskeleton are clearly visible with magnifying glass on the fracture surfaces. This type of flint is very common in the ...

Chert in dolomite rock

© J.Kornaga

Collected in a field near Chalfont S. Peter

Colorful chips of flint (mostly made of quartz, var. chalcedony) lying on the ground at the Alibates Flint Quarries National Monument, Potter County, Texas. The local American Indian population has worked the flint out of a dolomite rock of Permian age, in which it occurs in nodules. Field of view approximately 20cm.

© Amir Akhavan

Field of view is about 5mm. Photo and Collection, Martin Stolworthy. Forams and Micro Fossils in Flint.

© Martin Stolworthy

Extraordinary brown Menilite Opal recreating a humanoid shape (approx. 6 cm).

© Carlos Calvet - GemCat -

Fossil of a radiolarian skeleton in the white crust of the flint (specimen shown on photo 1), seen in a thin section. The once opaline skeleton has turned into chalcedony and the cavity inside the radiolarian skeleton has been filled with chalcedony that grew radially from the wall towards the center of the cavity. Don't be mistaken by the ...

© Amir Akhavan

Flint from Sintra collected in 2008. Rui Nunes' specimen and photo, June 2010.

© Rui Nunes 2010

Name: Polish Flint (light brown) Measurements: 35 x 13 cm Collected: Other - in the collection of Crater Rock Museum, Central Point, Oregon Photographer: Phyllis Richardson Info: Incredibly beautiful banding of Polish flint

© Crater Rock Museum

Flint nodules used in a wall construction in Etretat, Normandy, France. July 1, 2010.

Flint from an abandoned quarry at Malveira, Sintra Rui Nunes' specimen and photo, June 2010.

© Rui Nunes 2010

Polished section of Quartz (var. Flint) Specimen size 5x4 cm.Photo and collection GF. Capolupi

© Gianfranco Capolupi

Flint outcrop located in the back pit at Nether's Farm, Flint Ridge, Ohio. This piece is approximately 2ft long and a foot deep.

This is a specimen of menilite, also known as nodular opal, from the outcrops of opal deposits in the Agramón region. Although these opals most often exhibit rounded forms, they can occasionally develop more complex aggregates. Rui Nunes' collection and photo, 2006.

© Rui Nunes 2006

Disconnected fragments in cut flint nodule cemented again by white Cretaceous limestone. Diameter 210 mm. From 1995 roadworks. Collection and photo A. Zordan.

© Antonio Zordan

Menilite - brown nodular concretion.

© Christopher O'Neill

Opal - (to form sediment chemistry) with 7x6x2cm - April of 2002

© Photo & Collection of Martins da Pedra

Four small Menilite "dwarfs" made of more or less "hydrophaned" brown Opal (each 2-3 cm).

© Carlos Calvet - GemCat -

Sample with: 95x60x50mm

© Bruno Fonseca

Quartz variety "flint" filling a part of a Echinocorys sp. shell, rest filled with chalk-clay, showing how the sea-urchin was burried. Sample is 10 cm high and 10 cm wide. Collected and in the collection of the photographer. Photo taken 14. March 2008.

© Peter Andresen

A polished slab of Polish flint with its typical banding pattern. Size of specimen 95 x 72 mm.

© Amir Akhavan

Flint, field of view 50x40mm

Thin section of the black core of a flint nodule weathered out of Cretacean chalk rocks, viewed with crossed polarizers (specimen shown on photo 1). It is the same view as that shown in photo 2 done with parallel polarizers. The typical, apparently granular structure of the flint is revealed. Radially grown fibrous length-fast chalcedony is ...

© Amir Akhavan

Nódulo de 15 cm de sílex (flint) sobre caliza. Tamaño pieza: 16 x 12 cm. Colección y foto Rafa Muñoz.

© Rafa Muñoz Alvarado

Polished Menilite. The Hydrophane surface has been eliminated, showing the nice brown color of local Opal (approx. 6 cm).

© Carlos Calvet - GemCat -

The ranch advertises arrowheads and topaz. This is a scraper, fashioned from flint, 3.12"x1.25" See other picture for back. Flint different color that naturally occurring flint in area, so maybe brought in by native Commanche once.

© Paul J. Broyles 2011

This is a specimen of menilite, also known as nodular opal, from the outcrops of opal deposits in the Agramón region. Although these opals most often exhibit rounded forms, they can occasionally develop more complex aggregates. Rui Nunes' collection and photo, 2006.

© Rui Nunes 2006

This is a small cabinet specimen of flint and crystalline quartz from Flint Ridge, Hopewell, Ohio. Flint is considered to be a cryptocrystalline variety of silicon dioxide, similar in composition to chert (Akhaven, 2012), but nodular in origin. Akhaven (2012) noted that small cavities are often found in flint, with quartz being the dominant ...

© Jamison K. Brizendine

Specimen size: 7.5 x 6.5 cm. Photo and collection: Gf. Capolupi

© GF. Capolupi

This piece of Flint measures 2" x 2". I found this while on vacation in Texas with my Daddy. We climbed what the locals call "The Twin Sister" hills and found lots of flint and fossils.

Polished Flint from Licking County. Size: 45 X 35 mm

Flint With Nodules, "Mr. oooh" Collected by Barb Campbell in March 2011 in the vicinity of Stonehenge, Wiltshire England. Specimen 9.5cm x 9.5cm x 4.5cm Barb is my sister and she named this piece "Mr. oooh", two eyes and mouth....lol

© Lloyd Van Duzen

Three 2 - 3 cm long Menilites made of brown Opal (right) and Opal partially altered to Hydrophane (left).

© Carlos Calvet - GemCat -

Thin section of the black core of a flint nodule weathered out of Cretacean chalk rocks (specimen shown on photo 1). One can recognize small fossils and inclusions of mostly organic material. Normal light. Black and white photo. Field of view 1.2 mm.

© Amir Akhavan

Menilite - close-up of surface.

© Christopher O'Neill

At Caestert, flint does not only occur as nodules, but also forms vertical veins that cross the bedding of the rock and sometimes extend to several meters. This is a small part of such a vein, and it shows all features that can be seen in the common flint nodules, including a cortex and small vugs with quartz crystals. It probably has formed in ...

© Amir Akhavan

A grey flint nodule in limestone. Rui Nunes' photo, January 2012.

© Rui Nunes 2012

A really cool piece of brownish colored flint from the tallest peak in the Judean Desert. The locality is actually a truncated cone-shaped hill where Herod the Great built a fortress between 23 and 15 BC. It should be noted that Flint is not a mineral, but it's actually considered to be a rock comprising tiny grains of cryptocrystalline quartz. ...

© Brian Kosnar - Mineral Classics