Concretion

A concretion is a hard, compact mass of sedimentary rock formed by the precipitation of mineral cement within the spaces between the sediment grains. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin 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.

There is an important distinction to draw between concretions and nodules. Concretions are formed from mineral precipitation around some kind of nucleus while a nodule is a replacement body.

Descriptions dating from the 18th century attest to the fact that concretions have long been regarded as geological curiosities. Because of the variety of unusual shapes, sizes and compositions, concretions have been interpreted to be dinosaur eggs, animal and plant fossils (called pseudofossils), extraterrestrial debris or human artifacts.

Read more about Concretion:  Origins, Appearance, Composition, Occurrence, Gallery

Other articles related to "concretion, concretions":

Concretion - Gallery
... Concretions of various shapes Sandstone concretion formed around crystals Sandstone Concretion at Año Nuevo State Reserve Cannonball concretion in Jameson Land, East Greenland Fossiliferous ... is about 3 cm in diameter “Button Rock” concretions found within Schoharie County, New York ... Scalecube is one centimeter square Concretions of the Llewellyn Formation in the south wall of the Bear Valley Strip Mine, located west of Shamokin in Northumberland County ...
Physiology Of Dinosaurs - Cardiovascular System
... other researchers published a paper where they assert that the heart is really a concretion of entirely mineral "cement" ... of concentric layers in some places and another concretion is preserved behind the right leg ... their position they agreed that the chest did contain a type of concretion, but one that had formed around and partially preserved the more muscular portions of the ...
Kolponomos Newportensis
... skull, jaw and post-cranial bones found in a concretion of sediment ... The concretion was discovered in two pieces by fossil collector Douglas Emlong near Newport, Oregon, the first in 1969 and the second, eight years later ... Because the concretion had been hardened so much by tectonic stress, the paleontological laboratory at the Smithsonian Institution considered them "the most difficult materials ever ...
Dinosaur Egg - Identification - False Eggs
... Concretions Concretions are formed when decaying organisms change the chemistry of their immediate surroundings in a manner that is conducive to allowing minerals to ... The shape of the concretion only roughly reflects the shape of the decomposing organic matter that triggered its formation ... Instead the concretion's shape more closely reflects the extent that the decomposion has raised the pH of the local environment ...