Chert

related topics
{@card@, make, design}
{acid, form, water}
{island, water, area}
{build, building, house}
{language, word, form}
{ship, engine, design}

Chert (pronounced /ˈtʃɜrt/) is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color (from white to black), but most often manifests as gray, brown, grayish brown and light green to rusty red; 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).

Contents

Occurrence

Chert occurs 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, 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 geosynclinal deposits. These thickly bedded cherts include the novaculite of the Ouachita Mountains of Arkansas, Oklahoma, and similar occurrences in Texas 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.[1]

Terminology: "chert", "chalcedony" and "flint"

There is much confusion concerning the exact meanings and differences among the terms "chert", "chalcedony" and "flint" (as well as their numerous varieties). In petrology the term "chert" is used to refer generally to all rocks composed primarily of microcrystalline, cryptocrystalline and microfibrous quartz. The term does not include quartzite. Chalcedony is a microfibrous (microcrystaline with a fibrous structure) variety of quartz.

Full article ▸

related documents
Bakelite
Match
Chalcedony
Erlenmeyer flask
Marble
Optical brightener
Soapstone
Opal
Insulator (electrical)
Arc lamp
Pig iron
Fiber
Jasper
Nitrocellulose
Calotype
Preform
Triboluminescence
Prismatic blade
Knapping
Canvas work
Applique
Bifocals
Hydroxyproline
Amethyst
Aerobic organism
Metal matrix composite
Thymidine
Pyrophosphate
Pyruvic acid
Nuclide