Banded Iron Formation
Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock that are almost always of Precambrian age. A typical BIF consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shales and cherts, often red in color, of similar thickness, and containing microbands (sub-millimeter) of iron oxides. Some of the oldest known rock formations, formed over 3,700 million years ago, include banded iron layers. Banded layers rich in iron were a common feature in sediments for much of the Earth's early history but are now rare. Phanerozoic ironstones generally have a different genesis.
Read more about Banded Iron Formation: Relation To Atmospheric Oxygenation, Origins, Snowball Earth Scenario, Effect of Asteroid Impact
Famous quotes containing the words banded, iron and/or formation:
“That excitement about Kossuth, consider how characteristic, but superficial, it was!—only another kind of politics or dancing. Men were making speeches to him all over the country, but each expressed only the thought, or the want of thought, of the multitude. No man stood on truth. They were merely banded together, as usual one leaning on another, and all together on nothing.”
—Henry David Thoreau (1817–1862)
“Hate-hardened heart, O heart of iron,
iron is iron till it is rust.
There never was a war that was
not inward; I must
fight till I have conquered in myself what
causes war, but I would not believe it.”
—Marianne Moore (1887–1972)
“The moral virtues, then, are produced in us neither by nature nor against nature. Nature, indeed, prepares in us the ground for their reception, but their complete formation is the product of habit.”
—Aristotle (384–322 B.C.)