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Flint is a compact microcrystalline quartz. It was originally the name for chert found in chalk or marly limestone formations formed by a replacement of calcium carbonate with silica. Commonly found as nodules, this variety was often used in past times to make bladed tools. Today, some geologists refer to any dark gray to black chert as flint.
Chalcedony's standard chemical structure (based on the chemical structure of quartz) is SiO 2 (silicon dioxide). Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black.
Quartz is, therefore, classified structurally as a framework silicate mineral and compositionally as an oxide mineral. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. [9] Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation ...
Individual layers consist of translucent or opaque, microcrystalline, fibrous quartz called chalcedony. Impurities in different layers cause variations in color. Many agate masses are simply geodes that have completely filled up with quartz. Common agate colors are clearish-whitish-grayish, brownish-red, and yellowish-brown.
Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, [1] [2] is an opaque, [3] impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. Jasper breaks with a smooth surface and is used for ornamentation or as ...
Its color is normally apple-green, but varies from turquoise-like cyan to deep green. The darker varieties of chrysoprase are also referred to as prase . (However, the term prase is also used to describe chlorite -included quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.)
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, [1] [2] categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start fires. Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.
This conglomerate consists of pebbles and cobbles of white vein quartz, red and green quartzite, sandstone, red and gray chert, and red shale. The grayish-purple to grayish-red conglomerate and sandstone is cemented largely by hematite and microcrystalline quartz. The cobbles that it contains range in size from 2.5 in (6.4 cm) to 6.5 in (17 cm).
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