chert

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chert:

see flintflint,
variety of quartz that commonly occurs in rounded nodules and whose crystal structure is not visible to the naked eye. Flint is dark gray, smoky brown, or black in color; pale gray flint is called chert.
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Chert

 

a mineral formation consisting of crystalline and amorphous silica (opal, chalcedony, or quartz). Chert is widespread in nature in the form of concretions, nodules, and seams that either lie parallel with the enclosing limestone and chalk deposits or cut across bedding. It is formed either by diagenesis of deposits, by catagenesis of rocks, or by weathering. It has a hardness of 7 on the mineralogical scale and breaks with a conchoidal fracture. Because of its ability to form a sharp cutting edge when chipped, chert (flint) was used by man from the most ancient times to the Iron Age to make stone tools.

chert

[chərt]
(petrology)
A hard, dense, sedimentary rock composed of fine-grained silica, characterized by a semivitreous to dull luster and a splintery to conchoidal fracture; commonly gray, black, reddish brown, or green. Also known as hornstone; phthanite.

chert

A very fine-grained dense rock consisting of chalcedony or opal, often with some quartz, and sometimes with calcite, iron oxide, organic matter, or other impurities; has a homogeneous texture and white, gray, or black color; some of its constituents may react with cement alkalies and therefore may be undesirable as concrete aggregate for exposed concrete in northern climates.
References in periodicals archive ?
VMS deposits are commonly associated with regionally developed iron- and (or) manganese-rich metalliferous sediment and chert developed at the same time-stratigraphic horizon as the massive sulfide deposits.
Folk, "Exogenous carbonaceous microstructures in Early Archaean cherts and BIFs from the Isua Green-stone Belt: Implications for the search for life in ancient rocks," Precambrian Research, vol.
Caption: Billions of years ago, localized hydrothermal activity, not globally warm oceans, heated and altered this South African chert (rocks in the foreground) that formed on the seafloor.
Rhyolite, slightly coarser than the cherts and chalcedonies, also became relatively more prominent in C2, especially within the tool assemblage.
Brookite, the orthorhombic trimorph of [TiO.sub.2], occurs in fine, doubly terminated, deep reddish brown crystals in chert cutting Hale Creek, Trinity County, California.
More than 12,000 years ago, local natives started to quarry chert from a small Alibates-capped hill within the Canadian River Valley, and tribes continued to quarry the colorful chert for weapons and tools into historic time.
Both the Shepherds Bush and the Spotted Dog Prospects are topographically dominated by a ridge of outcropping chert and ironstone, with zones of brecciation, silicification and quartz veining along the strike of this unit.
Key words: geochemical analysis, energy dispersive X-ray fluorescence; Mackenzie Inuit, Dene, Kuukpak, lithic raw material procurement, quarry sites, Thunder River chert, oral history
Raw materials include banded light, dark grey and patinated cherts, but white quartzite predominates.
Bedrock consists of limestone, sandstone, shale, chert and mafic igneous rocks (Selkregg, 1974).
The gravel portion of the deposits are dominantly composed of chert commonly containing Paleozoic fossils of crinoids, brachiopods, corals, bryozoans, gastropods, stromatolites, stromotoporids, and rare trilobites.
The name New Harmony Group was proposed by Becker & Droste (1978) to include the Grassy Knob Chert, Backbone Limestone, and Clear Creek Chert (Fig.