Chert

Chert
Sedimentary rock
Chert
Chert

Chert ( t/) is a hard, fine-grained sedimentary rock composed of crystals of quartz (silica) that are very small (microcrystalline or cryptocrystalline).[1] Quartz (silica) is the mineral form of silicon dioxide (SiO2).[2] Chert is often of biological origin (organic) but may also occur inorganically as a chemical precipitate or a diagenetic replacement (e.g., petrified wood).[3] Geologists use chert as a generic name for any type of microcrystalline or cryptocrystalline quartz.

Chert is usually of biological origin, being the petrified remains of siliceous ooze, the biogenic sediment that covers large areas of the deep ocean floor, and which contains the silicon skeletal remains of diatoms, silicoflagellates, and radiolarians. Depending on its origin, it can contain either microfossils, small macrofossils, or both. It varies greatly in color (from white to black), but most often manifests as gray, brown, grayish brown and light green to rusty red (occasionally dark green too); its color is an expression of trace elements present in the rock, and both red and green are most often related to traces of iron (in its oxidized and reduced forms respectively).

Occurrence

Flint with white weathered crust

Chert occurs in carbonate rocks as oval to irregular nodules in greensand, limestone, chalk, and dolostone formations as a replacement mineral, where it is formed as a result of some type of diagenesis. Where it occurs in chalk or marl, it is usually called flint. It also occurs in thin beds, when it is a primary deposit (such as with many jaspers and radiolarites). Thick beds of chert occur in deep marine deposits. These thickly bedded cherts include the novaculite of the Ouachita Mountains of Arkansas, Oklahoma, and similar occurrences in Texas and South Carolina[4] in the United States. The banded iron formations of Precambrian age are composed of alternating layers of chert and iron oxides.

Chert also occurs in diatomaceous deposits and is known as diatomaceous chert. Diatomaceous chert consists of beds and lenses of diatomite which were converted during diagenesis into dense, hard chert. Beds of marine diatomaceous chert comprising strata several hundred meters thick have been reported from sedimentary sequences such as the Miocene Monterey Formation of California and occur in rocks as old as the Cretaceous.[5]

Other Languages
العربية: شيرت
català: Chert
čeština: Rohovec
español: Chert (roca)
فارسی: چرت
français: Chaille
Gaeilge: Seirt
한국어: 각암
Nederlands: Hoornsteen
norsk: Chert
norsk nynorsk: Chert
português: Cherte
română: Chert
Simple English: Chert
српски / srpski: Рожнац
svenska: Hornsten
Tiếng Việt: Chert