An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies; as a result, achondrites have distinct mineralogies indicative of igneous processes. Achondrites account for about 8% of meteorites overall, the majority of them are HED meteorites originating from the crust of asteroid 4 Vesta. Other types include Martian and several types thought to originate from as-yet unidentified asteroids; these groups have been determined on the basis of e.g. the Fe/Mn chemical ratio and the 17O/18O oxygen isotope ratios, thought to be characteristic "fingerprints" for each parent body. Achondrites are classified into the following groups: Primitive achondrites Asteroidal achondrites Lunar meteorites Martian meteorites Primitive achondrites called PAC group, are called in this way because their chemical composition is primitive in the sense that it is similar to the composition of chondrites, but their texture is igneous, indicative of melting processes.
To this group belong: Acapulcoites Lodranites Winonaites Ureilites Brachinites Asteroidal achondrites called evolved achondrites, are called in this way because have been differentiated on a parent body. This means that their mineralogical and chemical composition was changed by melting and crystallization processes, they are divided several groups: HED meteorites. They may have originated on the asteroid 4 Vesta, because their reflection spectra are similar, they are named after the initial letters of the three subgroups: Howardites Eucrites Diogenites Angrites Aubrites Lunar meteorites are meteorites that originated from the Moon. Martian meteorites are meteorites, they are divided into three main groups, with two exceptions: Shergottites Nakhlites Chassignites OPX martian meteorites Regolith/Soil samples Glossary of meteoritics Achondrite Images from Meteorites Australia
Queen Alexandra Range
The Queen Alexandra Range is a major mountain range of the Transantarctic Mountains System, located in the Ross Dependency region of Antarctica. It is about 160 km long, bordering the entire western side of Beardmore Glacier from the Polar Plateau to the Ross Ice Shelf. Alternate names for this range include Alexandra Mountains, Alexandra Range and Königin Alexandra Gebirge; the highest peak of the range is Mount Kirkpatrick at 4,528 metres. Other peaks in the range include Mount Dickerson; this mountain range was discovered on the journey toward the South Pole by the British Antarctic Expedition, was named by Ernest Shackleton for Queen Alexandra of England. Shackleton and his men, a expedition headed by Robert Falcon Scott, both collected rock samples from the range that contained fossils; the discovery that multicellular life forms had lived so close to the South Pole was an additional piece of evidence that accompanied the publication of the theory of continental drift. Ahmadjian Peak is a prominent ice-covered peak.
Named by Advisory Committee on Antarctic Names for Vernon Ahmadjian, United States Antarctic Research Program biologist at McMurdo Station, 1963-64. Mount Bishop stands 3.2 km south of Ahmadjian Peak. Named by US-ACAN after Lieutenant Barry Chapman Bishop, United States Air Force, an observer with the Argentine Antarctic Expedition. S. Antarctica Projects Officer, 1958 and 1959. Decennial Peak is a peak situated 4.8 km southwest of Mount Kirkpatrick. Mapped by United States Geological Survey from surveys and U. S. Navy air photos, 1958-65. Named by US-ACAN in recognition of the Decennial of the Institute of Polar Studies, Ohio State University, in 1970, the same year the University celebrated its Centennial; the university and the Institute have been active in Antarctic investigations since 1960. Mount Elizabeth is a large ice-free mountain 4,480 metres high situated 6 mi south of Mount Anne. Discovered by the British Antarctic Expedition and named for Elizabeth Dawson-Lambton, a supporter of the BAE.
Mount Fox is a mountain standing 1 mi SW of Mount F. L. Smith. Discovered and named by the British Antarctic Expedition. Mount Ida is a conspicuous bare rock mountain, standing 2 miles west of Granite Pillars, just southeast of the head of King Glacier. Discovered by the British Antarctic Expedition, named for Ida Jane Rule of Christchurch, New Zealand, who married Edward Saunders, Secretary to Shackleton, who assisted in preparing the narrative of the expedition. Mount Stanley stands northeast of the head of Wyckoff Glacier near the western limits of Grindley Plateau. Named by the British Antarctic Expedition for the eldest brother of Dr. E. S. Marshall, a member of the expedition; this identification is the New Zealand Geological Survey Antarctic Expedition interpretation of the original positioning by the British Antarctic Expedition. Morris Heights is a smooth ice-covered heights, forming a peninsula-like divide between Beaver and King Glaciers at the north end of Queen Alexandra Range. Named by Advisory Committee on Antarctic Names for Lieutenant Clarence T. Morris, U.
S. Navy, aerology officer on the staff of the Commander, U. S. Naval Support Force, Antarctica, 1962 and 1963
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the object enters the atmosphere, various factors such as friction and chemical interactions with the atmospheric gases cause it to heat up and radiate that energy, it becomes a meteor and forms a fireball known as a shooting star or falling star. Meteorites vary in size. For geologists, a bolide is a meteorite large enough to create an impact crater. Meteorites that are recovered after being observed as they transit the atmosphere and impact the Earth are called meteorite falls. All others are known as meteorite finds; as of August 2018, there were about 1,412 witnessed falls that have specimens in the world's collections. As of 2018, there are more than 59,200 well-documented meteorite finds. Meteorites have traditionally been divided into three broad categories: stony meteorites that are rocks composed of silicate minerals.
Modern classification schemes divide meteorites into groups according to their structure and isotopic composition and mineralogy. Meteorites smaller than 2 mm are classified as micrometeorites. Extraterrestrial meteorites are such objects that have impacted other celestial bodies, whether or not they have passed through an atmosphere, they have been found on the Mars. Meteorites are always named for the places they were found a nearby town or geographic feature. In cases where many meteorites were found in one place, the name may be followed by a number or letter; the name designated by the Meteoritical Society is used by scientists and most collectors. Most meteoroids disintegrate. Five to ten a year are observed to fall and are subsequently recovered and made known to scientists. Few meteorites are large enough to create large impact craters. Instead, they arrive at the surface at their terminal velocity and, at most, create a small pit. Large meteoroids may strike the earth with a significant fraction of their escape velocity, leaving behind a hypervelocity impact crater.
The kind of crater will depend on the size, degree of fragmentation, incoming angle of the impactor. The force of such collisions has the potential to cause widespread destruction; the most frequent hypervelocity cratering events on the Earth are caused by iron meteoroids, which are most able to transit the atmosphere intact. Examples of craters caused by iron meteoroids include Barringer Meteor Crater, Odessa Meteor Crater, Wabar craters, Wolfe Creek crater. In contrast relatively large stony or icy bodies like small comets or asteroids, up to millions of tons, are disrupted in the atmosphere, do not make impact craters. Although such disruption events are uncommon, they can cause a considerable concussion to occur. Large stony objects, hundreds of meters in diameter or more, weighing tens of millions of tons or more, can reach the surface and cause large craters, but are rare; such events are so energetic that the impactor is destroyed, leaving no meteorites. Several phenomena are well documented during witnessed meteorite falls too small to produce hypervelocity craters.
The fireball that occurs as the meteoroid passes through the atmosphere can appear to be bright, rivaling the sun in intensity, although most are far dimmer and may not be noticed during daytime. Various colors have been reported, including yellow and red. Flashes and bursts of light can occur. Explosions and rumblings are heard during meteorite falls, which can be caused by sonic booms as well as shock waves resulting from major fragmentation events; these sounds can be heard with a radius of a hundred or more kilometers. Whistling and hissing sounds are sometimes heard, but are poorly understood. Following passage of the fireball, it is not unusual for a dust trail to linger in the atmosphere for several minutes; as meteoroids are heated during atmospheric entry, their surfaces experience ablation. They can be sculpted into various shapes during this process, sometimes resulting in shallow thumbprint-like indentations on their surfaces called regmaglypts. If the meteoroid maintains a fixed orientation for some time, without tumbling, it may develop a conical "nose cone" or "heat shield" shape.
As it decelerates the molten surface layer solidifies into a thin fusion crust, which on most meteorites is black. On stony meteorites, the heat-affected zone is at most a few mm deep. Reports vary. Meteorites from multiple falls, such as Bjurbole, Tagish Lake, Buzzard Coulee, have been found having fallen on lake and sea ice suggesting that they were not hot when they
Regolith is a layer of loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rock, other related materials and is present on Earth, the Moon, some asteroids, other terrestrial planets and moons; the term regolith combines two Greek words: rhegos, "blanket", lithos, "rock". The American geologist George P. Merrill first defined the term in 1897, writing: In places this covering is made up of material originating through rock-weathering or plant growth in situ. In other instances it is of fragmental and more or less decomposed matter drifted by wind, water or ice from other sources; this entire mantle of unconsolidated material, whatever its nature or origin, it is proposed to call the regolith. Earth's regolith includes the following subdivisions and components: soil or pedolith alluvium and other transported cover, including that transported by aeolian, glacial and gravity flow processes. "saprolith'" divided into the upper saprolite: oxidised bedrock lower saprolite: chemically reduced weathered rocks saprock: fractured bedrock with weathering restricted to fracture margins.
Volcanic ash and lavas duricrust. It is formed by cementation of soils and transported material by clays, iron oxides and oxyhydroxides and sulfates, as well as less common agents, into indurated layers resistant to weathering and erosion. Groundwater- and water-deposited salts. Biota and organic components derived from it. Regolith can vary from being absent to hundreds of metres in thickness, its age can vary from instantaneous to hundreds of millions of years old. Regolith on Earth originates from biological processes. People call various types of earthly regolith by such names as dirt, gravel and mud. On Earth, the presence of regolith is one of the important factors for most life, since few plants can grow on or within solid rock and animals would be unable to burrow or build shelter without loose material. Regolith is important to engineers constructing buildings and other civil works; the mechanical properties of regolith vary and need to be documented if the construction is to withstand the rigors of use.
Regolith may host many mineral deposits, for example mineral sands, calcrete uranium, lateritic nickel deposits, among others. Elsewhere, understanding regolith properties geochemical composition, is critical to geochemical and geophysical exploration for mineral deposits beneath it; the regolith is an important source of construction material, including sand, crushed stone and gypsum. The regolith is the zone through which aquifers are recharged and through which aquifer discharge occurs. Many aquifers, such as alluvial aquifers, occur within regolith; the composition of the regolith can strongly influence water composition through the presence of salts and acid-generating materials. Regolith covers the entire lunar surface, bedrock protruding only on steep-sided crater walls and the occasional lava channel; this regolith has formed over the last 4.6 billion years from the impact of large and small meteoroids, from the steady bombardment of micrometeoroids and from solar and galactic charged particles breaking down surface rocks.
The impact of micrometeoroids, sometimes travelling faster than 96,000 km/h, generates enough heat to melt or vaporize dust particles. This melting and refreezing welds particles together into glassy, jagged-edged agglutinates, reminiscent of tektites found on Earth; the regolith is from 4 to 5 m thick in mare areas and from 10 to 15 m in the older highland regions. Below this true regolith is a region of blocky and fractured bedrock created by larger impacts, referred to as the "megaregolith"; the density of regolith at the Apollo 15 landing site averages 1.35 g/cm3 for the top 30 cm, it is 1.85g/cm3 at a depth of 60 cm. The term lunar soil is used interchangeably with "lunar regolith" but refers to the finer fraction of regolith, that, composed of grains one centimetre in diameter or less; some have argued that the term "soil" is not correct in reference to the Moon because soil is defined as having organic content, whereas the Moon has none. However, standard usage among lunar scientists is to ignore that distinction.
"Lunar dust" connotes finer materials than lunar soil, the fraction, less than 30 micrometers in diameter. The average chemical composition of regolith might be estimated from the relative concentration of elements in lunar soil; the physical and optical properties of lunar regolith are altered through a process known as space weathering, which darkens the regolith over time, causing crater rays to fade and disappear. During the early phases of the Apollo Moon landing program, Thomas Gold of Cornell University and part of President's Science Advisory Committee raised a concern that the thick dust layer at the top of the regolith would not support the weight of the lunar module and that the module might sink beneath the surface. However, Joseph Veverka pointed out that Gold had miscalculated the depth of the overlying dust, only a couple of centimeters thick. Indeed, the regolith was found to be quite firm by the robotic Surveyor spacecraft that preceded Apollo, during the Apollo landings the astronauts found it necessary to use a hammer to drive a core samplin
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix that can be similar to or different from the composition of the fragments. The word has its origins in the Italian language, in which it means either "loose gravel" or "stone made by cemented gravel". A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, tectonic breccia, igneous breccia, impact breccia, hydrothermal breccia. Sedimentary breccia is a type of clastic sedimentary rock, made of angular to subangular, randomly oriented clasts of other sedimentary rocks. A conglomerate, by contrast, is a sedimentary rock composed of rounded fragments or clasts of pre-existing rocks. Both breccia and conglomerate are composed of fragments averaging greater than 2 millimetres in size; the angular shape of the fragments indicates that the material has not been transported far from its source. Sedimentary breccia consists of angular, poorly sorted, immature fragments of rocks in a finer grained groundmass which are produced by mass wasting.
It is lithified scree. Thick sequences of sedimentary breccia are formed next to fault scarps in grabens. Breccia may occur along a buried stream channel where it indicates accumulation along a juvenile or flowing stream. Sedimentary breccia may be formed by submarine debris flows. Turbidites occur as fine-grained peripheral deposits to sedimentary breccia flows. In a karst terrain, a collapse breccia may form due to collapse of rock into a sinkhole or in cave development. Fault breccia results from the grinding action of two fault blocks. Subsequent cementation of these broken fragments may occur by means of the introduction of mineral matter in groundwater. Igneous clastic rocks can be divided into two classes: Broken, fragmental rocks associated with volcanic eruptions, both of the lava and pyroclastic type. Volcanic pyroclastic rocks are formed by explosive eruption of lava and any rocks which are entrained within the eruptive column; this may include rocks plucked off the wall of the magma conduit, or physically picked up by the ensuing pyroclastic surge.
Lavas rhyolite and dacite flows, tend to form clastic volcanic rocks by a process known as autobrecciation. This occurs when the thick, nearly solid lava breaks up into blocks and these blocks are reincorporated into the lava flow again and mixed in with the remaining liquid magma; the resulting breccia is uniform in rock chemical composition. Lavas may pick up rock fragments if flowing over unconsolidated rubble on the flanks of a volcano, these form volcanic breccias called pillow breccias. Within the volcanic conduits of explosive volcanoes the volcanic breccia environment merges into the intrusive breccia environment. There the upwelling lava tends to solidify during quiescent intervals only to be shattered by ensuing eruptions. Clastic rocks are commonly found in shallow subvolcanic intrusions such as porphyry stocks and kimberlite pipes, where they are transitional with volcanic breccias. Intrusive rocks can become brecciated in appearance by multiple stages of intrusion if fresh magma is intruded into consolidated or solidified magma.
This may be seen in many granite intrusions where aplite veins form a late-stage stockwork through earlier phases of the granite mass. When intense, the rock may appear as a chaotic breccia. Clastic rocks in mafic and ultramafic intrusions have been found and form via several processes: Consumption and melt-mingling with wall rocks, where the felsic wall rocks are softened and invaded by the hotter ultramafic intrusion. Impact breccias are thought to be diagnostic of an impact event such as an asteroid or comet striking the Earth and are found at impact craters. Impact breccia, a type of impactite, forms during the process of impact cratering when large meteorites or comets impact with the Earth or other rocky planets or asteroids. Breccia of this type may be present on or beneath the floor of the crater, in the rim, or in the ejecta expelled beyond the crater. Impact breccia may be identified by its occurrence in or around a known impact crater, and/or an association with other products of impact cratering such as shatter cones, impact glass, shocked minerals, chemical and isotopic evidence of contamination with extraterrestrial material.
An example of an impact breccia is the Neugrund breccia, formed in the Neugrund impact. Hydrothermal breccias form at shallow crustal levels between 150 and 350 °C, when seismic or volcanic activity causes a void to open along a fault deep underground; the void draws in hot water, as pressure in the cavity drops, the water violently boils. In addition, the sudden opening of a cavity causes rock at the sides of the fault to destabilise and implode inwards, the broken rock gets caught up in a churning mixture of rock and boiling water. Rock fragments collide with each other and the sides of the void, the angular fragments become more rounded. Volatile gases are lost to the steam phase in particular carbon dioxide; as a result, the chemistry of the fluids changes an
An atmosphere is a layer or a set of layers of gases surrounding a planet or other material body, held in place by the gravity of that body. An atmosphere is more to be retained if the gravity it is subject to is high and the temperature of the atmosphere is low; the atmosphere of Earth is composed of nitrogen, argon, carbon dioxide and other gases in trace amounts. Oxygen is used by most organisms for respiration; the atmosphere helps to protect living organisms from genetic damage by solar ultraviolet radiation, solar wind and cosmic rays. The current composition of the Earth's atmosphere is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms; the term stellar atmosphere describes the outer region of a star and includes the portion above the opaque photosphere. Stars with sufficiently low temperatures may have outer atmospheres with compound molecules. Atmospheric pressure at a particular location is the force per unit area perpendicular to a surface determined by the weight of the vertical column of atmosphere above that location.
On Earth, units of air pressure are based on the internationally recognized standard atmosphere, defined as 101.325 kPa. It is measured with a barometer. Atmospheric pressure decreases with increasing altitude due to the diminishing mass of gas above; the height at which the pressure from an atmosphere declines by a factor of e is called the scale height and is denoted by H. For an atmosphere with a uniform temperature, the scale height is proportional to the temperature and inversely proportional to the product of the mean molecular mass of dry air and the local acceleration of gravity at that location. For such a model atmosphere, the pressure declines exponentially with increasing altitude. However, atmospheres are not uniform in temperature, so estimation of the atmospheric pressure at any particular altitude is more complex. Surface gravity differs among the planets. For example, the large gravitational force of the giant planet Jupiter retains light gases such as hydrogen and helium that escape from objects with lower gravity.
Secondly, the distance from the Sun determines the energy available to heat atmospheric gas to the point where some fraction of its molecules' thermal motion exceed the planet's escape velocity, allowing those to escape a planet's gravitational grasp. Thus and cold Titan and Pluto are able to retain their atmospheres despite their low gravities. Since a collection of gas molecules may be moving at a wide range of velocities, there will always be some fast enough to produce a slow leakage of gas into space. Lighter molecules move faster than heavier ones with the same thermal kinetic energy, so gases of low molecular weight are lost more than those of high molecular weight, it is thought that Venus and Mars may have lost much of their water when, after being photo dissociated into hydrogen and oxygen by solar ultraviolet, the hydrogen escaped. Earth's magnetic field helps to prevent this, as the solar wind would enhance the escape of hydrogen. However, over the past 3 billion years Earth may have lost gases through the magnetic polar regions due to auroral activity, including a net 2% of its atmospheric oxygen.
The net effect, taking the most important escape processes into account, is that an intrinsic magnetic field does not protect a planet from atmospheric escape and that for some magnetizations the presence of a magnetic field works to increase the escape rate. Other mechanisms that can cause atmosphere depletion are solar wind-induced sputtering, impact erosion and sequestration—sometimes referred to as "freezing out"—into the regolith and polar caps. Atmospheres have dramatic effects on the surfaces of rocky bodies. Objects that have no atmosphere, or that have only an exosphere, have terrain, covered in craters. Without an atmosphere, the planet has no protection from meteoroids, all of them collide with the surface as meteorites and create craters. Most meteoroids burn up as meteors before hitting a planet's surface; when meteoroids do impact, the effects are erased by the action of wind. As a result, craters are rare on objects with atmospheres. Wind erosion is a significant factor in shaping the terrain of rocky planets with atmospheres, over time can erase the effects of both craters and volcanoes.
In addition, since liquids can not exist without pressure, an atmosphere allows liquid to be present at the surface, resulting in lakes and oceans. Earth and Titan are known to have liquids at their surface and terrain on the planet suggests that Mars had liquid on its surface in the past. A planet's initial atmospheric composition is related to the chemistry and temperature of the local solar nebula during planetary formation and the subsequent escape of interior gases; the original atmospheres started with a rotating disc of gases that collapsed to form a series of spaced rings that condensed to form the planets. The planet's atmospheres were modified over time by various complex factors, resulting in quite different outcomes; the atmospheres of the planets Venus and Mars are composed of carbon dioxide, with small quantities of nitrogen, argon and traces of other gases. The composition of Earth's atmosphere is governed by the by-products of the life that it sust
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