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Cryptocrystalline
Cryptocrystalline is a rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light. Among the sedimentary rocks, chert and flint are cryptocrystalline. Carbonado, a form of diamond, is also cryptocrystalline. Volcanic rocks, especially of the felsic type such as felsites and rhyolites, may have a cryptocrystalline groundmass as distinguished from pure obsidian (felsic) or tachylyte (mafic), which are natural rock glasses. Agate and onyx are examples of cryptocrystalline silica ( chalcedony). See also * List of rock textures * Macrocrystalline * Microcrystalline * Nanocrystalline A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Defi ... * Rock microstructure References ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chert
Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood. Chert is typically composed of 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. Precambrian cherts are notable for the presence of fossil cyanobacteria. In addition to microfossils, chert occasionally contains macrofossils. However, some chert is devoid of any fossils. Chert varies greatly in color (from white to black), but most often manifests as gray, brown, grayish brown and light green to rusty redW.L. Roberts, T.J. Campbell, G.R. Rapp Jr., "Encyclopedia of Mineralogy, Second Edition", 1990. R.S. Mitc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chalcedony
Chalcedony ( , or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Chalcedony's standard chemical structure (based on the chemical structure of quartz) is SiO2 ( 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. The color of chalcedony sold commercially is often enhanced by dyeing or heating. The name ''chalcedony'' comes from the Latin ''chalcedonius'' (alternatively spelled ''calchedonius'') and is probably derived from the town of Chalcedon in Turkey. The name appears in Pliny the Elder's '' Naturalis Historia'' as a term for a translucent kind of jaspis. Another reference to a gem by the name of ''k ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macrocrystalline
In geology, macrocrystalline rocks have crystals large enough to easily be identified by sight. Macrocrystalline or phaneritic texture is common in intrusive igneous rocks which cooled slowly enough for crystal growth. Pegmatites are noted for very large crystal size. Rocks with crystals requiring microscopic or X-ray analysis for identification are termed microcrystalline or cryptocrystalline Cryptocrystalline is a rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light. Among the sedimentary rocks, chert and flint are crypt .... Mineralogy Petrology {{petrology-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Matrix (geology)
The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic, crystals in which larger crystals, called phenocrysts, are embedded. This porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix. Also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock (kimberlite) called "yellow ground". The matrix of sedimentary rocks is finer-grained sedimentary material, such as clay or silt, in which larger grains or clasts are embedded. It is also used to describe the rock material in which a fossil is embedded. Cementation All sediments are at first in an incoherent condition (e.g. sands, clays and gravels, beds of shells), and they may remain in this state for an indefinite period. Millions of years h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flint
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start fires. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.''The Flints from Portsdown Hill'' Inside the nodule, flint is usually dark grey, black, green, white or brown in colour, and often has a glassy or waxy appearance. A thin layer on the outside of the nodules is usually different in colour, typically white and rough in texture. The nodules can often be found along streams and be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing as a compound of several minerals and as a synthetic product. Notable examples include fused quartz, fumed silica, silica gel, opal and aerogels. It is used in structural materials, microelectronics (as an electrical insulator), and as components in the food and pharmaceutical industries. Structure In the majority of silicates, the silicon atom shows tetrahedral coordination, with four oxygen atoms surrounding a central Si atomsee 3-D Unit Cell. Thus, SiO2 forms 3-dimensional network solids in which each silicon atom is covalently bonded in a tetrahedral manner to 4 oxygen atoms. In contrast, CO2 is a linear molecule. The starkly different structures of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Onyx
Onyx primarily refers to the parallel banded variety of chalcedony, a silicate mineral. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colors of its bands range from black to almost every color. Commonly, specimens of onyx contain bands of black and/or white. Onyx, as a descriptive term, has also been applied to parallel banded varieties of alabaster, marble, calcite, obsidian and opal, and misleadingly to materials with contorted banding, such as "Cave Onyx" and "Mexican Onyx". Etymology ''Onyx'' comes through Latin (of the same spelling), from the Ancient Greek , meaning "claw" or "fingernail". Onyx with flesh-colored and white bands can sometimes resemble a fingernail. The English word "nail" is cognate with the Greek word. Varieties Onyx is formed of bands of chalcedony in alternating colors. It is cryptocrystalline, consisting of fine intergrowths of the silica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agate
Agate () is a common rock formation, consisting of chalcedony and quartz as its primary components, with a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate was common in Ancient Greece, in assorted jewelry and in the seal stones of Greek warriors, while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus Valley civilisation. Etymology The stone was given its name by Theophrastus, a Greek philosopher and naturalist, who discovered the stone along the shore line of the Dirillo River or Achates ( grc, Ἀχάτης) in Sicily, sometime between the 4th and 3rd centuries BCE. Formation and properties Agate minerals have the tendency to form on or within pre-existing rocks, creating difficulties in accurately determining their time of formation. Their host rocks have been dated to have formed as early as the Archean Eon. Agates are most commonly found as nodules wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tachylyte
Tachylite ( ; also spelled tachylyte) is a form of basaltic volcanic glass. This glass is formed naturally by the rapid cooling of molten basalt. It is a type of mafic igneous rock that is decomposable by acids and readily fusible. The color is a black or dark-brown, and it has a greasy-looking, resinous luster. It is very brittle and occurs in dikes, veins, and intrusive masses. The word originates from the Ancient Greek , meaning "swift". Tachylites have the appearance of pitch and are often more or less vesicular and sometimes spherulitic. They are very brittle and break down readily under a hammer. Small crystals of feldspar or olivine are sometimes visible in them with the unaided eye. All tachylites weather rather easily and by oxidation of their iron become dark brown or red. Three modes of occurrence characterize this rock. In all cases they are found under conditions which imply rapid cooling, but they are much less common than acid volcanic glasses (or obsidi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystals
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations. The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification. The word ''crystal'' derives from the Ancient Greek word (), meaning both " ice" and " rock crystal", from (), "icy cold, frost". Examples of large crystals include snowflakes, diamonds, and table salt. Most inorganic solids are not crystals but polycrystals, i.e. many microscopic crystals fused together into a single solid. Polycrystals include most metals, rocks, ceramics, and ice. A third categor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rock Microstructure
Rock microstructure includes the texture and small-scale structures of a rock. The words ''texture'' and ''microstructure'' are interchangeable, with the latter preferred in modern geological literature. However, ''texture'' is still acceptable because it is a useful means of identifying the origin of rocks, how they formed, and their appearance. Textures are ''penetrative fabrics'' of rocks; they occur throughout the entirety of the rock mass on a microscopic, hand-specimen, and often outcrop scale. This is similar in many ways to foliations, except a texture does not necessarily carry structural information in terms of deformation events and orientation information. Structures occur on a hand-specimen scale and above. Microstructure analysis describes the textural features of the rock, and can provide information on the conditions of formation, petrogenesis, and subsequent deformation, folding, or alteration events. Sedimentary microstructures Description of sedimentary ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nanocrystalline
A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definitions vary, but nanocrystalline material is commonly defined as a crystallite (grain) size below 100 nm. Grain sizes from 100–500 nm are typically considered "ultrafine" grains. The grain size of a NC sample can be estimated using x-ray diffraction. In materials with very small grain sizes, the diffraction peaks will be broadened. This broadening can be related to a crystallite size using the Scherrer equation (applicable up to ~50 nm), a Williamson-Hall plot, or more sophisticated methods such as the Warren-Averbach method or computer modeling of the diffraction pattern. The crystallite size can be measured directly using transmission electron microscopy. Synthesis Nanocrystalline materials can be prepared in se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
