How are nodules formed in geology?

How are nodules formed in geology?

Nodules form due to chemical reactions in the sediment often very soon after burial, whilst the rest of the sediment is still soft. Localised chemical conditions cause the rock to harden (cementation).

What are nodule rocks?

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. They can be found in sandstone, shale or limestone.

How do iron nodules form?

Their formation has been variously ascribed to volcanic activity; rhythmic deposition from iron and silica solutions due to seasonal variations; oxidation of iron-rich sediments contemporaneous with deposition; and precipitation from solution as a result of special oxidation-reduction conditions.

How do pyrite nodules form?

Pyrite nodules have been identified in many sedimentary rocks and their formation has attracted much interest. The lack of zonation suggests that it formed early during sedimentation when the pore waters were still connected with the overlying water column.

Where are manganese nodules found in the ocean?

Abstract. Manganese nodules have a widespread occurrence on the sediment-covered seafloor of the NE Pacific in about 4000–6000 m water depth and form an important habitat for deep-sea fauna.

How do flint nodules form?

How is it formed? Flint forms during or after the chalk in which it is found. Flint nodules grow within the sediment by being precipitated from solutions which are rich in silica. The silica probably came from the silica-rich skeletons of the animals which make up the chalk.

Where are concretions found?

Concretions are found in a variety of rocks, but are particularly common in shales, siltstones, and sandstones. They often outwardly resemble fossils or rocks that look as if they do not belong to the stratum in which they were found.

Are concretions rocks?

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.

Where are Septarian nodules located?

Septarian nodules, sometimes called lightning stones, can also found on the Lake Michigan shoreline as well as in New Zealand, England, Morocco, and Madagascar. Septarians are composed of calcite (the yellow centers), aragonite (the brown lines), and limestone (the outer grey surface).

What is concretion and nodules?

A concretion is a clearly bound body of rock within generally softer enclosing sediments of the same composition. Nodules are hard bodies of rock similar to concretions, though of different composition than the sediments that contain them.

Where do manganese nodules form?

Manganese Nodules. Manganese nodules (also referred to as polymetallic nodules) are spherical precipitates of manganese, iron oxides and other metals (e.g., copper, cobalt, and zinc) that form around a core material, such as a shell fragment or shark’s tooth.

Where do phosphate rich nodules form?

Significant deposits of phosphorite are found in the Xisha Islands (Ritterbush, 1978). Phosphorite is also formed in regions of oceanic upwelling where large volumes of phosphate-rich cold water rise from great depths to the surface.

What does a nodule look like in rock?

Nodule. 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 is a nodular sedimentary rock?

Nodular is used to describe a sediment or sedimentary rock composed of scattered to loosely packed nodules in matrix of like or unlike character. It is also used to describe mineral aggregates that occur in the form of nodules, e.g. colloform mineral aggregate with a bulbed surface.

What type of nodules are found in limestone?

Nodule. 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. Clay ironstone, a mixture of clay and siderite (iron carbonate), sometimes occurs as layers of dark-gray to brown, fine-grained nodules overlying coal seams.

Which of the following minerals typically form nodules?

Minerals that typically form nodules include calcite, chert, apatite (phosphorite), anhydrite, and pyrite. Nodular is used to describe a sediment or sedimentary rock composed of scattered to loosely packed nodules in matrix of like or unlike character.