The L type ordinary chondrites are the second most common group of meteorites, accounting for 35% of all those catalogued, 40% of the ordinary chondrites. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively, their name comes from their low iron abundance, with respect to the H chondrites, which are about 20–25% iron by weight. The L chondrites have been named hypersthene chondrites or olivine hypersthene chondrites for the dominant minerals, but these terms are now obsolete. Characteristic is the fayalite content in olivine of 21 to 25 mol%. About 4–10% iron–nickel is found as a free metal, making these meteorites magnetic, but not as as the H chondrites; the most abundant minerals are hypersthene, as well as iron -- nickel and troilite. Chromite, sodium-rich feldspar and calcium phosphates occur in minor amounts. Petrologic type 6 dominates, with over 60% of the L chondrites falling into this class.
This indicates. Many of the L chondrite meteors may have their origin in the Ordovician meteor event. Compared to other chondrites, a large proportion of the L chondrites have been shocked, taken to imply that the parent body was catastrophically disrupted by a large impact; this event has been radioisotope dated to around 470±6 million years ago. The parent body/bodies for this group are not known, but plausible suggestions include 433 Eros and 8 Flora, or the Flora family as a whole. 433 Eros has been found to have a similar spectrum, while several pieces of circumstantial evidence for the Flora family exist: the Flora family is thought to have formed about 1,000 to 500 million years ago. Glossary of meteoritics The Catalogue of Meteorites
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites; the C chondrites represent. Some famous carbonaceous chondrites are: Allende, Orgueil, Murray, Tagish Lake, Sutter's Mill. Carbonaceous chondrites are grouped according to distinctive compositions thought to reflect the type of parent body from which they originated; these C chondrite groups are now each named with a standard two-letter CX designation, where C stands for "carbonaceous" plus a capital letter in the spot X, often the first letter of the name of a prominent meteorite—often the first to be discovered—in the group. Such meteorites are named for the place where they fell, thus giving no clue as to the physical nature of the group. Group CH, where H is for "high metal" is so far the only exception. See below for name derivations of each group. Several groups of carbonaceous chondrites, notably the CM and CI groups, contain high percentages of water, as well as organic compounds.
They are composed of silicates and sulfides, with the minerals olivine and serpentine being characteristic. The presence of volatile organic chemicals and water indicates that they have not undergone significant heating since they were formed, their compositions are considered to be close to that of the solar nebula from which the Solar System condensed. Other groups of C chondrites, e.g. CO, CV, CK chondrites, are poor in volatile compounds, some of these have experienced significant heating on their parent asteroids; this group, named after the Ivuna meteorite, have chemical compositions that are close to that measured in the solar photosphere. In this sense, they are chemically the most primitive known meteorites. CI chondrites contain a high proportion of water, organic matter in the form of amino acids and PAHs. Aqueous alteration promotes a composition of hydrous phyllosilicates and olivine crystals occurring in a black matrix, a possible lack of chondrules, it is thought they have not been heated above 50 °C, indicating that they condensed in the cooler outer portion of the solar nebula.
Five CI chondrites have been observed to fall: Ivuna, Alais and Revelstoke. Several others have been found by Japanese field parties in Antarctica. In general, the extreme fragility of CI chondrites causes them to be susceptible to terrestrial weathering, they do not survive on Earth's surface for long after they fall; this group takes its name from Vigarano. Most of these chondrites belong to the petrologic type 3. CV chondrites observed falls: Allende Bali Bukhara Grosnaja Kaba Mokoia Vigarano The group takes its name from Mighei, but the most famous member is the extensively studied Murchison meteorite. Many falls of this type have been observed and CM chondrites are known to contain a rich mix of complex organic compounds such as amino-acids and purine/pyrimidine nucleobases. CM chondrite famous falls: Murchison Sutter's Mill The group takes its name from Renazzo; the best parent body candidate is 2 Pallas. CR chondrites observed falls: Al Rais Kaidun RenazzoOther famous CR chondrites: Dar al Gani 574 El Djouf 001 NWA 801 "H" stands for "high metal" because CH chondrites may contain up to as much as 40% of metal.
That makes them the most metal-rich of any chondrite group. The first meteorite discovered was ALH 85085. Chemically, these chondrites are related to CR and CB groups. All specimens of this group belong only to petrologic types 2 or 3; the group takes its name from the most representative member: Bencubbin. Although these chondrites contain over 50% nickel-iron metal, they are not classified as mesosiderites because their mineralogical and chemical properties are associated with CR chondrites; this group take its name from Karoonda. These chondrites are related to the CO and CV groups; the group take its name from Ornans. The chondrule size is only about 0.15 mm on average. They are all of petrologic type 3. Famous CO chondrite falls: Ornans Kainsaz Warrenton MossFamous finds: Dar al Gani 749 The most famous members: Tagish Lake Ehrenfreund et al. found that amino acids in Ivuna and Orgueil were present at much lower concentrations than in CM chondrites, that they had a distinct composition high in β-alanine, glycine, γ-ABA, β-ABA but low in α-aminoisobutyric acid and isovaline.
This implies that they had formed by a different synthetic pathway, on a different parent body from the CM chondrites. Most of the organic carbon in CI and CM carbonaceous; that is similar to the description for kerogen. A kerogen-like material is in the ALH84001 Martian meteorite; the CM meteorite Murchison has over 70 extraterrestrial amino acids and other compounds including carboxylic acids, hydroxy carboxylic acids and phosphonic acids, aliphatic and polar hydrocarbons, heterocycles, carbonyl compounds, alcohols and amides. Glossary of meteoritics List of meteorite minerals Carbonaceous chondrites at The Encyclopedia of Astrobiology and Spaceflight Gilmour, I.. Origins of earth and life. Bletchley: The Open University. ISBN 978-0-7492-8182-3. Carbonaceous Chondrite Images from Meteorites Australia - Meteorites
Graphite, archaically referred to as plumbago, is a crystalline form of the element carbon with its atoms arranged in a hexagonal structure. It occurs in this form and is the most stable form of carbon under standard conditions. Under high pressures and temperatures it converts to diamond. Graphite is used in lubricants, its high conductivity makes it useful in electronic products such as electrodes and solar panels. The principal types of natural graphite, each occurring in different types of ore deposits, are Crystalline small flakes of graphite occurs as isolated, plate-like particles with hexagonal edges if unbroken; when broken the edges can be angular. Ordered pyrolytic graphite refers to graphite with an angular spread between the graphite sheets of less than 1°; the name "graphite fiber" is sometimes used to refer to carbon fibers or carbon fiber-reinforced polymer. Graphite occurs in metamorphic rocks as a result of the reduction of sedimentary carbon compounds during metamorphism, it occurs in igneous rocks and in meteorites.
Minerals associated with graphite include quartz, calcite and tourmaline. The principal export sources of mined graphite are in order of tonnage: China, Canada and Madagascar. In meteorites, graphite occurs with silicate minerals. Small graphitic crystals in meteoritic iron are called cliftonite; some microscopic grains have distinctive isotopic compositions, indicating that they were formed before the Solar system. They are one of about 12 known types of mineral that predate the Solar System and have been detected in molecular clouds; these minerals were formed in the ejecta when supernovae exploded or low- to intermediate-sized stars expelled their outer envelopes late in their lives. Graphite may be the third oldest mineral in the Universe. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond; the two most common are graphite. In diamond the bonds are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors. In graphite they are sp2 orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart.
The individual layers are called graphene. In each layer, the carbon atoms are arranged in a honeycomb lattice with separation of 0.142 nm, the distance between planes is 0.335 nm. Atoms in the plane are bonded covalently, with only three of the four potential bonding sites satisfied; the fourth electron is free to migrate in the plane. However, it does not conduct in a direction at right angles to the plane. Bonding between layers is via weak van der Waals bonds, which allows layers of graphite to be separated, or to slide past each other; the two known forms of graphite and beta, have similar physical properties, except that the graphene layers stack differently. The alpha graphite may be either buckled; the alpha form can be converted to the beta form through mechanical treatment and the beta form reverts to the alpha form when it is heated above 1300 °C. The equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally.
The pressure changes linearly between 1.7 GPa at 0 K and 12 GPa at 5000 K. However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, 20 °C and 1 standard atmosphere, the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible. However, at temperatures above about 4500 K, diamond converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa is needed; the acoustic and thermal properties of graphite are anisotropic, since phonons propagate along the bound planes, but are slower to travel from one plane to another. Graphite's high thermal stability and electrical and thermal conductivity facilitate its widespread use as electrodes and refractories in high temperature material processing applications. However, in oxygen-containing atmospheres graphite oxidizes to form carbon dioxide at temperatures of 700 °C and above.
Graphite is hence useful in such applications as arc lamp electrodes. It can conduct electricity due to the vast electron delocalization within the carbon layers; these valence electrons are free to move. However, the electricity is conducted within the plane of the layers; the conductive properties of powdered graphite allow its use as pressure sensor in carbon microphones. Graphite and graphite powder are valued in industrial applications for their self-lubricating and dry lubricating properties. There is a common belief that graphite's lubricating properties are due to the loose interlamellar coupling between sheets in the structure. However, it has been shown that in a vacuum environment, graphite degrades as a lubricant, due to the hypoxic conditions; this observation led to the hypothesis that the lubrication is due to the presence of fluids between the layers, such as air and water, which are adsorbed from the
Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron rich endmember of the pyrrhotite group. Pyrrhotite has the formula FeS, iron deficient; as troilite lacks the iron deficiency which gives pyrrhotite its characteristic magnetism, troilite is non-magnetic. Troilite can be found as a native mineral on Earth but is more abundant in meteorites, in particular, those originating from the Moon and Mars, it is among the minerals found in samples of the meteorite that struck Russia on February 15th, 2013. Uniform presence of troilite on the Moon and on Mars has been confirmed by the Apollo and Phobos space probes; the relative intensities of isotopes of sulfur are rather constant in meteorites as compared to the Earth minerals, therefore troilite from Canyon Diablo meteorite is chosen as the international sulfur isotope ratio standard. Troilite has hexagonal structure, its unit cell is a combination of two vertically stacked basic NiAs-type cells of pyrrhotite, where the top cell is diagonally shifted.
For this reason, troilite is sometimes called pyrrhotite-2C. A meteorite fall was observed in 1766 at Albareto, Italy. Samples were collected and studied by Domenico Troili who described the iron sulfide inclusions in the meteorite; these iron sulfides were long considered to be pyrite. In 1862 German mineralogist Gustav Rose analyzed the material and recognized it as stoichiometric FeS and gave it the name troilite in recognition of the work of Domenico Troili. Troilite has been reported from a variety of meteorites occurring with daubréelite, sphalerite, a variety of phosphate and silicate minerals, it has been reported from serpentinite in the Alta mine, Del Norte County, California and in layered igneous intrusions in Western Australia, the Ilimaussaq intrusion of southern Greenland, the Bushveld Complex in South Africa and at Nordfjellmark, Norway. In the South African and Australian occurrence it is associated with copper, platinum iron ore deposits occurring with pyrrhotite, mackinawite, valleriite and pyrite.
Troilite is rarely encountered in the Earth's crust. Most troilite on Earth is of meteoritic origin. One iron meteorite, Mundrabilla contains 25 to 35 volume percent troilite; the most famous troilite-containing meteorite is Canyon Diablo. Canyon Diablo Troilite is used as a standard of relative concentration of different isotopes of sulfur. Meteoritic standard was chosen because of the constancy of the sulfur isotopic ratio in meteorites, whereas the sulfur isotopic composition in Earth materials varies due to the bacterial activity. In particular, certain sulfate reducing bacteria can reduce 32SO2−4 1.07 times faster than 34SO2−4, which may increase the 34S/32S ratio by up to 10%. Troilite is the most common sulfide mineral at the lunar surface, it forms about one percent of the lunar crust and is present in any rock or meteorite originating from moon. In particular, all basalts brought by the Apollo 11, 12, 15 and 16 missions contain about 1% of troilite. Troilite is found in Martian meteorites.
Similar to the Moon's surface and meteorites, the fraction of troilite in Martian meteorites is close to 1%. Based on observations by the Voyager spacecraft in 1979 and Galileo in 1996, troilite might be present in the rocks of Jupiter’s satellites Ganymede and Callisto. Whereas experimental data for Jupiter's moons are yet limited, the theoretical modeling assumes large percentage of troilite in the core of those moons. Glossary of meteoritics
The term strewnfield indicates the area where meteorites from a single fall are dispersed. There are two strewnfield formation mechanisms: Mid-air fragmentation: when a large meteoroid enters the atmosphere, it fragments into many pieces before touching the ground, due to thermal shock; this mid-air explosion disperses the material over a large oval-shaped area. The long axis of this oval is along the flight path of the meteoroid; when multiple explosions occur, the material can be found in several overlapping ovals. Impact fragmentation: when there is no mid-air fragmentation, the fragmentation can occur upon impact. In this case, the strewnfield shape can be different circular. In the case of mid-air fragmentation, smaller fragments tend to fall shorter; that is why the biggest fragment is found at one end of the oval. In order to get an idea of the original flight direction, it is necessary to analyze the size pattern of the material over the strewnfield. Fragments of about 1 to 5 grams can be picked up on weather radar, as they fall at terminal velocity.
Glossary of meteoritics
The ordinary chondrites are a class of stony chondritic meteorites. They comprise about 87 % of all finds. Hence, they have been dubbed "ordinary"; the ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively. It is suspected that they are not representative of typical asteroid parent bodies, but rather of a select few which are advantageously placed to send impact fragments to Earth-crossing orbits; such positions secular resonances in the main asteroid belt. In fact, only the one rather insignificant asteroid 3628 Božněmcová has been identified to have a spectrum close to the ordinary chondrites. A probable parent body of the H chondrites is 6 Hebe, but its spectrum is dissimilar due to what is a metal impact melt component, it is that the ordinary chondrites comprise a detailed sample of but a few select asteroids which happen to have been in the right place at the right time to send many fragments toward Earth at the present moment in solar system history.
On the other hand, observations of 243 Ida by the Galileo spacecraft found weathering of Ida's surface, the reflection spectra of freshly exposed parts of the surface resembled that of OC meteorites, while the older regions matched the spectra of common S-type asteroids. The ordinary chondrites comprise three mineralogically and chemically distinct groupings, they differ in the amount of total iron, of iron metal and iron oxide in the silicates: The H chondrites have the Highest total iron, high metal, but lower iron oxide in the silicates The L chondrites have Lower total iron, lower metal, but higher iron oxide in the silicates The LL chondrites have Low total iron and Low metal, but the highest iron oxide content in the silicates. Glossary of meteoritics Chondrite Chondrule The Catalogue of Meteorites A Pictorial of Ordinary Chondrites - Meteorites Australia Gallery of Ordinary Chondrites by James St. John, a geologist at Ohio State University
Glossary of meteoritics
This is a glossary of terms used in meteoritics, the science of meteorites. 2 Pallas – an asteroid from the asteroid belt and one of the parent bodies of the CR meteorites. 4 Vesta – second-largest asteroid in the asteroid belt and source of the HED meteorites. 221 Eos – an asteroid from the asteroid belt and one of the parent bodies of the CO meteorites. 289 Nenetta – an asteroid from the asteroid belt and one of the parent bodies of the angrites. 3103 Eger – an asteroid from the asteroid belt and one of the parent bodies of the aubrites. 3819 Robinson – an asteroid from the asteroid belt and one of the parent bodies of the angrites. IA meteorite – an iron meteorite group now part of the IAB group/complex. IAB meteorite – an iron meteorite and primitive achondrite of the IAB group/complex. IB meteorite – an iron meteorite group now part of the IAB group/complex. IC meteorite – an iron meteorite, part of the IC group. Ablation – the process of a meteorite losing mass during the passage through the atmosphere.
Acapulcoite – a group of primitive achondrites. Accretion – the process in which matter of the protoplanetary disk coalesces to form planetesimals. Achondrite – a differentiated meteorite. Aerolite – an old term for stony meteorites. ALH – an abbreviation used for meteorites from Allan Hills. Allan Hills – a mountain chain in Antarctica where meteorites are concentrated by ice movements and can be spotted in the snow. Allan Hills 84001 – is an exotic meteorite from Mars that does not fit into any of the SNC groups and was thought to contain evidence for life on Mars. Allende meteorite – is the largest carbonaceous chondrite found on Earth. Amphoterite – an obsolete classification of chondritic meteorites that are now classified as LL. Angrite – a basaltic meteorite. Anomalous – meteorites that have properties that are unusual for their group or grouplet. ANSMET – the ANtarctic Search for METeorites is scientific program that looks for meteorites in the Transantarctic Mountains. Asteroidal achondrite – an achondrite that differentiated on an asteroid or planetesimal Asteroid spectral types – classification of asteroids according to their spectra.
Ataxite – an iron meteorite that has no visible structures when etched. Basaltic achondrite – a grouping of basalt meteorites Brachinite – either a primitive achondrite or an asteroidal achondrite C – can refer to carbonaceous chondrite or to an iron meteorite designation. Carbonaceous chondrite CAI – an abbreviation of Calcium-aluminium-rich inclusion Calcium-aluminium-rich inclusion Chassignite Chondrite – stony meteorites unmodified by melting or differentiation of the parent body Chondrule – millimetre-scale round grains found in chondrites Clan – meteorites that are not similar enough to form a group, but are not too different from each other to be put in separate classes. Class – two or more groups that have a similar chemistry and oxygen isotope ratios. Compositional type – a classification based on overall composition, for example stony, stony-iron. Can refer to the composition deduced from spectroscopy of asteroids. Condensation – the process of chemicals changing from the gaseous to the solid phase during the cooling of the protoplanetary disk.
Condensation sequence – the sequence of minerals that changes from the gaseous to the solid state while the protoplanetary disk cools. Cosmic dust – small interplanetary and interstellar particles that are similar to meteorites. Cosmochemistry – the science of the chemistry of the Solar System, based in part on the chemistry of meteorites. Dar al Gani – a meteorite field in the Libyan Sahara. Desert glass – natural glass found in deserts formed from the silica in sand as a result of lightning strikes or meteor impacts. Differentiated – a meteorite that has undergone igneous differentiation. Differentiation – the process of a planetesimal forming an iron core and silicate mantle. Duo – a grouping of two meteorites that share similar characteristics. E -- can refer to an iron meteorite designation. Eagle Station grouplet – a set of pallasite meteorite specimen that don't fit into any of the defined pallasite groups. Electrophonic bolide – a meteoroid which produces a measurable discharge of electromagnetic energy during its passage through the atmosphere.
Enstatite achondrite – a meteorite, composed of enstatite. Part of the aubrite group. Enstatite chondrite – a rare form of meteorite thought to comprise only 2% of chondrites. Fall – a meteorite, seen while it fell to Earth and found. Find – a meteorite, found without seeing it fall. Fossil meteorite - a meteorite, buried under layers of sediment before the start of the Quaternary period; some or all of the original cosmic material has been replaced by diagenetic minerals.. Fragment – a part of a meteorite that broke during passage through the atmosphere. Fragmentation – the process in which a meteorite breaks while falling through the atmosphere. Fusion crust – a coating on meteorites that forms during their passage through the atmosphere. Group – a collection of more than 5 meteorites sharing similar characteristics. Grouplet – a collection of less than 5 meteorites sharing similar characteristics. HED – abbreviation for three basaltic achondrite groups howardite and diogenite. HED meteorite – a clan of basaltic achondrites.
Hexahedrite – a structural class of iron meteorites having a low nickel content Hunter – a person who searches for meteorites. Impact breccia – rock composed of fragm