Generally, calcareous concretions are valued much like pearls. Brighter colors and stronger saturations command higher prices. Rounds and ovals are more desirable, and other shapes are judged based on how symmetrical they appear. Smoother surfaces, higher luster, and larger sizes also increase value.

How do you identify a concretion?

A concretion consists of the same material as the rock around it, plus the cementing mineral, whereas a nodule (like flint nodules in limestone) is composed of different material. Concretions can be shaped like cylinders, sheets, nearly perfect spheres, and everything in between. Most are spherical.

Are concretions fossils?

Concretions are commonly misunderstood geologic structures. Often mistaken for fossil eggs, turtle shells, or bones, they are actually not fossils at all but a common geologic phenomenon in almost all types of sedimentary rock, including sandstones, shales, siltstones, and limestones.

What does a concretion look like?

Concretions are often ovoid or spherical in shape, although irregular shapes also occur. ... 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.

How do you break open a concretion?

The best method to open concretions is to alternately freeze and thaw them. Put the concretions in a bucket of water and allow them to soak for several days so the water thoroughly penetrates the concretion. Then, place the bucket of concretions in a freezer.

Crackin' The Concretion Open - What's inside?

38 related questions found

What is inside a concretion?

Stratigraphic nomenclature: How rocks are named

Concretions are masses of mineral matter embedded within rock layers, including limestone, sandstone, and shale. They often take shape when minerals precipitating (settling) out of water collect around a nucleus, such as a pebble, leaf, shell, bone, or fossil.

How long do concretions take to form?

"However, our results show that concretions grow at a very fast rate over several months to several years." This rapid sealing mechanism could explain why some concretions contain well-preserved fossils of soft tissues that are rarely fossilized under other conditions.

What do fossil nodules look like?

The formation of nodules within sediments is often vital for good fossil preservation. Nodules are rounded lumps of hard stone found within mudstones and limestones, which are often small but may reach metres in size. They are clearly distinct from the surrounding rock known as matrix.

What does concretion mean?

1 : something concreted: such as. a : a hard usually inorganic mass (such as a bezoar or tophus) formed in a living body. b : a mass of mineral matter found generally in rock of a composition different from its own and produced by deposition from aqueous solution in the rock.

What is tiny concretion in kidney?

Renal concretions, commonly known as kidney stones, are small crystal lumps of different substances, such as salt, calcium, uric acid, and other minerals. They form as hard, pebble-like deposits which can range from anywhere between the size of a kernel to a grain of salt, or a sugar cube to a ping pong ball.

What are perfectly round rocks called?

Completely round rocks, known as concretions, are simply a natural phenomenon.

Why are pebbles round?

Transport of pebbles in a stream causes them to collide and rub against one another and the stream bed, and the resulting abrasion produces the familiar smooth and rounded shape of river rocks.

How do rock nodules form?

Chert and flint nodules are often found in beds of limestone and chalk. They form from the redeposition of amorphous silica arising from the dissolution of siliceous spicules of sponges, or debris from radiolaria and the postdepositional replacement of either the enclosing limestone or chalk by this silica.

What is a concretion in the eye?

Concretions are small white or yellowish dots, usually less than 1mm in diameter, commonly seen on the undersides of the eyelids. They contain cell debris and calcium. They may be the result of past inflammation. Occasionally they cause irritation or the feeling that there is something in the eye.

What causes cross bedding?

Cross-bedding is formed by the downstream migration of bedforms such as ripples or dunes in a flowing fluid. ... Cross-bedding can form in any environment in which a fluid flows over a bed with mobile material. It is most common in stream deposits (consisting of sand and gravel), tidal areas, and in aeolian dunes.

What's inside a geode?

Most geodes contain clear quartz crystals, while others have purple amethyst crystals. Still others can have agate, chalcedony, or jasper banding or crystals such as calcite, dolomite, celestite, etc. There is no easy way of telling what the inside of a geode holds until it is cut open or broken apart.

How do you tell if a rock is a nodule?

A nodule rock is a solid rock with no hollow center. So unlike geodes, the interior of a nodule rock contains no empty space. It does, however, contain minerals. Nodule rocks are harder than the rocks that surround them.

What does a nodule rock look like?

Nodules commonly are elongate with a knobby irregular surface; they usually are oriented parallel to the bedding. Chert and flint often occur as dense and structureless nodules of nearly pure silica in limestone or chalk, where they seem to be replacements of the carbonate rock by silica.

What do you call a concretion of earthy or mineral matter?

(Entry 1 of 7) 1 : a concretion of earthy or mineral matter: a(1) : such a concretion of indeterminate size or shape. (2) : rock.

What is calcareous concretions?

Calcareous concretions are pearl-like growths produced in mollusks that lack nacre. While still composed of calcite and aragonite, the crystals are much coarser. Some of these “pearls” may have a flame-like sheen on their surface. Calcareous concretions seen in jewelry include Conch Pearls and Quahogs.

What is iron concretion?

Iron oxide concretions are formed from post depositional, paleogroundwater chemical interaction with iron minerals in porous sedimentary rocks. The concretions record a history of iron mobilization and precipitation caused by changes in pH, oxidation conditions, and activity of bacteria.

What are conglomerate rocks?

Conglomerate is a sedimentary rock made of rounded pebbles and sand that is usually held together (cemented) by silica, calcite or iron oxide. It is a stone similar to sandstone but the rock particles are rounded or angular gravel rather than sand.

What does a rock hammer look like?

Shape. Geologist's hammers, as with most hammers, have two heads, one on either side. Most commonly, the tool consists of a flat square head on one end, with either a chisel or a pick head at the other end. A corner or edge of the flat head is used to deliver a blow to a rock with the intention of splitting it.