banded-iron formation

banded-iron formation

      chemically precipitated sediment, typically thin bedded or laminated, consisting of 15 percent or more iron of sedimentary origin and layers of chert, chalcedony, jasper, or quartz. Such formations occur on all the continents and usually are older than 1.7 billion years. They also are highly metamorphosed. Most BIFs contain iron oxides—hematite with secondary magnetite, goethite, and limonite—and are commonly used as low-grade iron ore (e.g., as in the Lake Superior region of North America). Because BIFs apparently have not formed since Precambrian time, special conditions are thought to have existed at the time of their formation. Considerable controversy exists over BIF origin, and a number of theories have been proposed. 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.

* * *


Universalium. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Banded iron formation — Banded iron formations (also known as banded ironstone formations or BIFs) are a distinctive type of rock often found in primordial (Precambrian) sedimentary rocks. The structures consist of repeated thin layers of iron oxides, either magnetite… …   Wikipedia

  • Banded Iron Formation — Bändereisenerz aus Nordamerika, 2,1 Milliarden Jahre alt Bändereisenerz von Upper Michigan, U.S.A. Ein Bändererz ist ein eisenhaltiges, marines …   Deutsch Wikipedia

  • Iron ore — Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in colour from dark grey, bright yellow, deep purple, to rusty red. The iron itself is usually found in the …   Wikipedia

  • Iron — Fe redirects here. For other uses, see Fe (disambiguation). This article is about the chemical element. For other uses, see Iron (disambiguation). manganese …   Wikipedia

  • Formation (stratigraphy) — A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties. Formations are not defined on the… …   Wikipedia

  • Channel-iron deposits — (CID) are iron rich fluvial sedimentary deposits of possible Miocene age occupying meandering palaeochannels in the Early to Mid Tertiary Hamerlsey palaeosurface of Western Australia. Examples are also known from Kazakhstan. The deposits are… …   Wikipedia

  • Mesabi Iron Range — Die Mesabi Range liegt westlich des Lake Superior und nördlich von Duluth Bergleute bei der Arb …   Deutsch Wikipedia

  • sedimentary rock — Rock formed at or near the Earth s surface by the accumulation and lithification of fragments of preexisting rocks or by precipitation from solution at normal surface temperatures. Sedimentary rocks can be formed only where sediments are… …   Universalium

  • Slave craton — which is one of the oldest dated rock units on Earth at 4.03 Ga. The crust of the Slave craton is thought to have amalgamated during a 2.69 Ga collision between a proto Slave western basement complex, known as the Central Slave Basement Complex,… …   Wikipedia

  • Precambrian time — Interval of geologic time from с 3. 8 billion years ago, the age of the oldest known rocks, to 544 million years ago, the beginning of the Cambrian Period. This interval represents more than 80% of the geologic record and thus provides important… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”