Nodule (geology)

Source: Wikipedia, the free encyclopedia.
Devonian nodular limestone
Concretionary nodular limestone at Jinshitan Coastal National Geopark, Dalian
, China

In

strata. In general, they lack any internal structure except for the preserved remnants of original bedding or fossils. Nodules are closely related to concretions and sometimes these terms are used interchangeably. Minerals that typically form nodules include calcite, chert, apatite (phosphorite), anhydrite, and pyrite.[1][2]

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.[1]

Nodule is also used for widely scattered concretionary lumps of manganese, cobalt, iron, and nickel found on the floors of the world's oceans. This is especially true of manganese nodules. Manganese and phosphorite nodules form on the seafloor and are syndepositional in origin. Thus, technically speaking, they are concretions instead of nodules.[1][2]

Chert and

spicules of sponges, or debris from radiolaria and the postdepositional replacement of either the enclosing limestone or chalk by this silica.[2]

See also

  • Chert – Hard, fine-grained sedimentary rock composed of cryptocrystalline silica
  • Flint – Cryptocrystalline form of the mineral quartz

References