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Chert (/ tʃ ɜːr t /) is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, [1] the mineral form of silicon dioxide (SiO 2). [2] Chert is characteristically of biological origin, but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood. [3]
When opal silica accumulates faster than it dissolves, it is buried and can provide a diagenetic environment for marine chert formation. [8] The processes leading to chert formation have been observed in the Southern Ocean, where siliceous ooze accumulation is the fastest. [8] Chert formation however can take tens of millions of years. [7]
The compaction of radiolarites is dependent on their chemical composition and correlates positively with the original SiO 2-content. The compaction factor varies generally between 3.2 and 5, which means that 1 meter of consolidated sediment is equivalent to 3.2 to 5 meters of ooze.
To reduce susceptibility to fragmentation, flint/chert may be heat-treated, being slowly brought up to a temperature of 150 to 260 °C (300 to 500 °F) for 24 hours, then slowly cooled to room temperature. This makes the material more homogeneous and thus more knappable and produces tools with a cleaner, sharper cutting edge. Heat treating was ...
The size of the oolites reflect the time that they were exposed to the water before they were covered with later sediment. Oolites are often used in the home aquarium industry because their small grain size (0.2 to 1.22 mm) is ideal for shallow static beds and bottom covering of up to 1" in depth.
In Poland, quartzite deposits at surface level exists in Świętokrzyskie Mountains. In Norway, deposits are quarried near Austertana , [ 19 ] which is one of the largest quarries in the world at 850,000 tonnes (840,000 long tons; 940,000 short tons) annually, and Mårnes near Sandhornøya with an output of 150,000 tonnes (150,000 long tons ...
Banded iron formation from the Barberton Greenstone Belt, South Africa. A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe 3 O 4) or hematite (Fe 2 O 3), alternating with bands of iron-poor chert, often red in color, of similar thickness.
While crystalline magnesite has a well developed crystal structure, the cryptocrystalline magnesite is amorphous- mostly aggregate of fine grains. Since clumped isotopic composition depends on specific bonding, difference in crystal structure is very likely to affect the way clumped isotopic signatures are recorded in these different structures.