CH3 chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More
Found September 30, 1991 27° 41.40′ N., 4° 22.72′ E. In the initial discovery in 1990, two pieces of an Fe-rich, fine-grained carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than Click on Term to Read More, weighing together 166 g, were found in the Algerian Sahara Desert and given the name Acfer 182. In 1991, additional pieces paired with Acfer 182 were found, including a 105 g piece designated Acfer 207 and two pieces with a combined weight of 612 g designated Acfer 214.
This meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More has chemical, mineralogical, and textural similarities to the unique 11.9 g chondritic brecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Click on Term to Read More ALH 85085, and has close affinities to the CR chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More and the newly designated CB chondrites. In light of their high bulk iron and metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn Click on Term to Read More content, both Acfer 182 (and pairings) and ALH 85085 were initially designated as ‘HH chondrites’ (Bischoff et al., 1992). However, due to their many similarities to carbonaceous chondrites they were given the new designation of ‘CH chondrites’ (Bischoff et al, 1993). More recently, several separate finds from Antarctica were included in this rare CH group (EET 96238, PAT 91546, PCA 91467, and RKP 92435), as well as additional finds from northwest Africa (NWA 470, NWA 739, NWA 770, and NWA 4781) and Oman (SaU 290). These carbonaceous chondrite groups considered together have been termed the CR clan.
Acfer 214 is composed primarily of chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More and chondruleRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More fragments (~70 vol%). Interestingly, it has a much lower abundance of complete chondrules than chondrule fragments, with some fragments being derived from larger chondrules than those now present. Most chondrules in Acfer 214 and other CH members are significantly smaller than those in other chondrite groups. The majority of the chondrules (~80%) are of the much rarer cryptocrystallineCrypto meaning "hidden" refers to a rock texture in which individual crystals are too small to be distinguished even using a standard petrographic microscope. Crystals are typically less than a few μm in size - any smaller and the texture would be considered amorphous. Among sedimentary terrestrial rocks, chert and Click on Term to Read More texture rather than porphyritic, and they have a mean diameter of 0.03–0.15 mm, the largest measuring 1.1 mm in diameter. Most magnesian and ferroan cryptocrystalline chondrules in CH chondrites have identical chemical and O-isotopic values to those of CB cryptocrystalline chondrules, and the two groups are considered to be genetically related (Nakashima et al., 2010).
However, some cryptocrystalline and porphyritic chondrules in CH chondrites have anomalous isotopic values compared to other carbonaceous chondrite groups, inferring that these CH chondrules originated in a separate nebular region and/or during a different time period. VolatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). depletions in these crptocrystalline chondrules suggest that they formed in high temperature conditions and cooled rapidly (Nakashima et al., 2011). An extremely 16O-rich, cryptocrystalline chondrule has been identified in Acfer 214 (Kobayashi et al., 2003). This chondrule, among others, condensed as a liquid directly from a nebular reservoir (Varela et al., 2011). It contains a lighter O signature than even refractory inclusionsInclusions found predominantly in carbonaceous chondrites and are rich in refractory elements particularly calcium, aluminum and titanium that in various combinations form minerals such as spinel, melilite, perovskite and hibonite. There are two types of refractory inclusion: • Ca Al-rich inclusions (CAIs) • Amoeboid olivine aggregates (AOAs) Refractory inclusions were Click on Term to Read More, and is the most 16O-enriched component discovered in a meteorite thus far.
Leitner et al. (2018) identified two presolar silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the grains (O-rich stardust grains) and four presolar SiC grains in the fine-grained material of the hydrated lithic clasts from the paired Acfer 182, representing a bulk abundance of 4 (+5/–2) ppmParts per million (106). Click on Term to Read More and 21 (+16/–10) ppm, respectively. Both of the silicate dust grains belong to group 1 of Nittler et al. (1997, article), which were derived from low-mass (1.2–2.2 M⊙) AGB-stage red giantGiant and highly luminous red star in the later stages of stellar evolution after it has left the main sequence. These red stars have a relatively cool surface whose core has burned most of its hydrogen. Red giants lose parts of their atmospheres and thus provide new elements into interstellar Click on Term to Read More stars. They note that presolar silicate grains are susceptible to destruction by aqueous alteration while SiC grains are not, and infer that the lithic clasts are consistent with petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes. 2.
Rare carbonaceous chondrite fragments present in Acfer 214 contain silica-rich spherules composed of nanocrystalline quartzComposed of SiO2, quartz is one of the silica group minerals most common in Earth's crust, but never found in meteorites as inclusions visible to the naked eye. Quartz in meteorites has been found in very small quantities in eucrites, other calcium-rich achondrites, and in the highly reduced E chondrites1. Click on Term to Read More formed at very high temperatures. The spherules subsequently underwent supercooling until rapid crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. Click on Term to Read More ensued. The consistently small size of this and all of the other components in this meteorite probably reflects aerodynamic size sorting in the nebulaAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive Click on Term to Read More region prior to accretionAccumulation of smaller objects into progressively larger bodies in the solar nebula leading to the eventual formation of asteroids, planetesimals and planets. The earliest accretion of the smallest particles was due to Van der Waals and electromagnetic forces. Further accretion continued by relatively low-velocity collisions of smaller bodies in the Click on Term to Read More, possibly through size-dependent interactions between gas drag pulling inward and photophoresis and radiation pressureMinute pressure exerted by electromagnetic radiation (such as but not limited to light from the sun) on everything it encounters. This can be thought of as the transfer of momentum from photons as they strike the surface of the object. In the environs of stars such pressure can become important Click on Term to Read More pushing outward (Haack et al., 2006). Alternatively, size-sorting could have been controlled by the abundance of dust in the nebular region and by the number of chondrule remelting episodes that occurred (Rubin, 2010). According to thermal models of Scott et al. (2007), the accretion of CH chondrites is consistent with late accretion ~3–5 m.y. after CAISub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More formation, at a time when radiogenic heating by 26Al was minimal. The formation location was likely in the outer region of the asteroid beltBelt located between 2.12 and 3.3 AU from the Sun and located between the orbits of Mars and Jupiter containing the vast majority of asteroids. The asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such Click on Term to Read More.
FeNi-metal is present in higher concentrations (~20 vol%) than in most other carbonaceous chondrites, which, taken together with the volatile- and sulfide-depletions observed, is indicative of an early accretion through condensation in a very hot (~1000°C at 10 Pa) nebular environment; these high temperatures are sustained by transient heating events associated with impact shocks. A nebular fractional condensation model is suggested by the widely varied patterns of zoning observed in some of these sub-mm-sized metal grains for the siderophile elements Ni, Co, Cr, P, Si, AuThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The Click on Term to Read More, Os, Ir, Ru, and Pd. To account for the preservation of these primitive zoned metal grains, as well as their virtual lack of Ga and Ge, it is necessary that these grains were isolated from the residual hot nebular gas before temperatures dropped below ~527°C. After condensing near 1 AU, these grains could have been radially transported to cooler nebular regions where oxidationOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons, while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More, sulfurization, and thermal metamorphism effects were minimal, and cooling was rapid—measured in hours or days. Although a primary martensitic structure was retained in most of the FeNi-metal grains (Kimura et al., 2008), exsolutionSegregation, during cooling, of a homogeneous solid solution into two or more different solids. Click on Term to Read More of Ni-rich taeniteLess common than kamacite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Taenite, γ-(Fe,Ni), has 27-65 wt% Ni, and forms small crystals that appear as highly reflecting thin ribbons on the etched surface of a meteorite; the name derives from the Greek word for "ribbon." Click on Term to Read More has been observed in some of the zoned metal grains, attesting to a brief period of reheating (hours to a day) and subsequent cooling at a reducedOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons, while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More rate (Goldstein et al., 2007).
A population of unzoned metal grains that are depleted in Ni and refractory siderophile elements are present, possibly forming a continuum with zoned metal grains. These grains condensed at a later, lower-temperature stage than the zoned metal grains from a gas previously depleted in refractory elementsUsing research by Wood (2019), any of the elements with a relatively high condensation temperature of 1291 K < TC,50 < 1806 K in the solar nebula1. They are the first elements to condense out of a cooling gas. Refractory elements are the main building blocks of rocky planets, dwarf Click on Term to Read More. Moreover, they could have remained longer within the gas environment (> ~10 weeks) and undergone diffusive equilibration of metal (Campbell and Humayun, 2004). Some of these grains were plastically deformed and experienced a brief period of reheating (hours to a day), as evidenced by a recrystallized structure and Ni-rich taenite exsolution phases (Goldstein et al., 2007). It is considered likely that this reheating/exsolution stage occurred after the metal grains were incorporated into the precursor aggregate of the chondrules, where the heating is attributed to impact events. Ultimately, brecciationThe formation of a breccia through a process by which rock fragments of of various types are recemented or fused together. Click on Term to Read More on the CH parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More brought together the various metal grains into the meteorites that we observe.
A silica-rich component (>65 wt% silicaSilicon dioxide, SiO2.), which comprises <0.1 vol% of the meteorite, has recently been studied by Hezel et al. (2003). Based on the chemical compositions of these silica-rich objects, as well as on the sequence of layers that is recorded in one object, an origin through fractional condensation from an evaporated nebular gas was proposed. Initially, Ca–Al–Ti-rich minerals were isolated from the residual gas, followed in the condensation sequence by forsteritePure* magnesium end-member (Mg2SiO4) of the olivine solid solution series and an important mineral in meteorites. When magnesium (Mg) is completely substituted by iron, it yields the the pure Fe-olivine end member, fayalite (Fe2SiO4). The various Fe and Mg substitutions between these two end-members are described based on their forsteritic (Fo) Click on Term to Read More and enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3). Click on Term to Read More, the formation of which left the residual gas enriched in SiO and infused with precursory silica-rich material. This precursor material was then reheated to temperatures above 1695°C, at which point several different silica-rich phases condensed—quartz, cristobaliteHigh temperature polymorph of silicon dioxide (SiO2). Has the same chemical composition as coesite, stishovite, seifertite and tridymite but possesses a different crystal structure. This silica group mineral occurs in terrestrial volcanic rocks, martian and lunar meteorites, chondrites and impact glasses like Libyan Desert Glass. Cristobalite has a very open Click on Term to Read More, glass, and an unidentified polymorph—followed by rapid cooling to form the glassy objects, or slower cooling to form the crystalline objects. While the porphyritic chondrules may have been produced during this transient high-temperature reheating phase, evidence suggests that the cryptocrystalline chondrules were likely formed and isolated earlier during fractional condensation processes. Finally, each of these types of objects were accreted into the CH chondriteRare carbonaceous chondrite class that is chemically very close to the CRs and CBs as evidenced by the CH/CBb meteorite Isheyevo. The "H" stands for "high metal" since the CH chondrites contain up to 15 vol. % Fe-Ni metal. The first CH chondrite was found in the Antarctic Allan Hills Click on Term to Read More body.
A small component within Acfer 214 consists of dark, fine-grained inclusions with phyllosilicate-rich clasts. Since the other CH components did not experience alteration, aqueous alteration of these dark hydrated clasts occurred prior to their being incorporated into the CH parent body. Also present are very small (up to 0.45 mm), extremely refractory, rimmed CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More that are high in grossiteCalcium aluminate, CaAl4O7, first found in metamorphosed Israeli limestone and recently in CAIs in CV3 and CR-CH-CB carbonaceous chondrites. Click on Term to Read More, meliliteGroup of minerals found in the CAIs of meteorites such as CV chondrites. Melilite consists almost exclusively of the binary solid solution gehlenite (Ca2Al2SiO7) – åkermanite (Ca2MgSi2O7). The melilite in CAIs is closer to gehlenite in composition. The first-formed (highest-temperature) melilite crystallizing from a melt is relatively aluminum-rich and becomes progressively Click on Term to Read More, hiboniteRefractory mineral, Ca-aluminate (CaAl12O19) that occurs in terrestrial metamorphic rocks and in CAIs of many chondrites. Meteoritic hibonite tends to be blue as seen in the meteorite Isheyevo (Ch/CB). Hibonite is one of the most refractory minerals found in primitive meteorites. Click on Term to Read More, and perovskiteTerm applied to A2+B4+O3 high-pressure minerals with a perovskite structure (general formula ABX3) where "A" is a metal that forms large cations such as Mg, Fe or Ca, "B" is another metal that forms smaller cations such as Si (called silicate perovskite), Ti and to a lesser degree Al, and Click on Term to Read More occur throughout (~0.1 vol%); some CAIs are significantly less altered than those from other carbonaceous chondrites. An exceedingly rare phase, Ca-monoaluminate, has been identified in the CH group member NWA 470, the first time that this phase has been found in nature. This Ca-monoaluminate is thought to have condensed from a dust-enriched region of the nebula. Since these highly refractory CAIs are depleted in 26Mg, they probably condensed at a very early stage, prior to the injection of 26Al into the nascent solar nebulaThe primitive gas and dust cloud around the Sun from which planetary materials formed.. Alternatively, production of this radionuclideRadioactive isotope - Atomic nuclide that decays radioactively . Click on Term to Read More may have been a more localized process that left it absent in the CAI condensation region. The remaining component of Acfer 214 consists of a sparse, fine-grained, chondritic matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More (~5 vol%) not present in other CH members, which has been terrestrially altered to a large degree. Due to extended weathering of the large metal component in Acfer 214, and its conversion to pore-filling iron oxide, the porosityThe volume percentage of a rock that consists of void space. Vesicular porosity is a type of porosity resulting from the presence of vesicles, or gas bubbles, in igneous rock such as the pumice presented here. Vesicular porosity is very rare in meteorites and is often associated with slag, one Click on Term to Read More was calculated to be 0 (Macke et al., 2011).
The presence of solar noble gasesElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. Click on Term to Read More and the fragmental nature of the components indicates that the CH chondrites were once located in a brecciated surface regolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles). Click on Term to Read More. Similar to bencubbinites, CH chondrites contain heavy 15N thought to have been accreted from interstellar molecular clouds. Although the actual source of the heavy N remains a source of study, it is thought to have been initially located within carbon-silicate aggregates, and then subsequently redistributed to other phases through shock heating or hydrous alteration. An alternative scenario proposed by Perron and Mostefaoui (2007) calls for the 15N to be delivered by a lagging portion of a hydrated cometary object impacting onto the CH parent body after some degree of cooling of the initial impact plume. They further argued that the data support an origin for the 15N within N-rich molecules rather than from meteoritic, carbonaceous material. In their in-depth study of Bencubbin, Perron et al. (2007) proposed that water and 15N-bearing organics were degassed from the hydrated clasts during the impact of a chondritic object(s). These hydrated clasts were agglomerated onto the Bencubbin parent body during its initial accretionary stages.
Extraterrestrial amino acids (13–16 ppm) were found to be present in a sampling of CH chondrites studied by Burton et al. (2013), abundances of which are similar to those found among CM2 chondrites. The types of amino acids are different from those identified in other carbonaceous chondrite groups and were likely synthesized through different chemical pathways under different environmental conditions (e.g., degree of aqueous alteration).
The relatively late formation of the CH chondrites is considered to have been concordant with, and related to the highly-energetic event that produced the CB chondrites, likely within an impact-generated plume. MineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous Click on Term to Read More components studied in Acfer 214 and Acfer 182 are consistent with an accretionary origin from such an event (Krot et al., 2014). Further information about this collisional event can be found on the Bencubbin page. Also, see the HaH 237 page for a detailed scenario of the CB group formation process ascertained by Fedkin et al. (2015) through kinetic condensation modeling.
Acfer 182, 207, 214, and ALH 85085, along with several meteorites found more recently are designated CH chondrites. They constitute a group of volatile-poor, high-metal, carbonaceous chondrites that represent the most pristine nebular condensates known, or more likely, a late-stage condensateIn the solar nebula, product of a chemical condensation reaction where a mineral phase precipitates (condenses) directly from a cooling vapor. Click on Term to Read More origin in a relatively high molecular weight gas such as a debris plume produced by a high-energy protoplanetary collision (Richter et al., 2014). It is notable that both Acfer 214 and NWA 739 share some anomalous features compared to the other CH chondrites, including larger-sized chondrules and O-isotopic compositions that plot outside of the CH field (they are also not concordant with each other). These two meteorites may represent a daughter parent body that is similar to, but separate from that of other CH chondrites.
The formation of Mercury from similar metal-rich chondritic material has been hypothesized to account for its high densityMass of an object divided by its volume. Density is a characteristic property of a substance (rock vs. ice, e.g.). Some substances (like gases) are easily compressible and have different densities depending on how much pressure is exerted upon them. The Sun is composed of compressible gases and is much Click on Term to Read More and large coreIn the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. Click on Term to Read More, just as have all of the inner planets to explain their volatile elementSubstance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of Click on Term to Read More depletions. Reflectance specta of asteroid 21 Lutetia (Xk or Xc type in Bus-DeMeo taxonomy, M-type in Tholen taxonomy) obtained by ESA’s Rosetta spacecraft is a very close match to laboratory spectra of CH3 chondrite PCA 91467 across a wide range of wavelengths for a variety of parameters, and it is considered to be a good candidate source body for this meteorite group (Trigo-Rodriguez et al., 2012; Moyano-Cambero et al., 2013, 2014, 2016). The data indicate that Lutetia may have a partially differentiated structure, with a metallic core, a silicate mantleMain silicate-rich zone within a planet between the crust and metallic core. The mantle accounts for 82% of Earth's volume and is composed of silicate minerals rich in Mg. The temperature of the mantle can be as high as 3,700 °C. Heat generated in the core causes convection currents in Click on Term to Read More, and a primitive chondritic crustOutermost layer of a differentiated planet, asteroid or moon, usually consisting of silicate rock and extending no more than 10s of km from the surface. The term is also applied to icy bodies, in which case it is composed of ices, frozen gases, and accumulated meteoritic material. On Earth, the Click on Term to Read More. The degree of aqueous alteration on Lutetia is higher than for PCA 91467, which could reflect collisional exposure of deeper crustal regions on the asteroid subsequent to the impact ejection of CH chondrites (Moyano-Cambero et al., 2016). A density estimate for Lutetia is similar to the bulk density calculated for the metal-rich CH group (Moyano-Cambero et al., 2016 and references therein). It was inferred that the specific source location for the CH chondrites could reside near the northern equatorial region of this heterogeneous asteroid, or it could derive from an asteroid having similar properties (Moyano-Cambero et al., 2014).
The specimen of Acfer 214 shown above and in the top photo below is a 1.5 g partial slice exhibiting an abundance of metal grains throughout. The bottom photo shows the main massLargest fragment of a meteorite, typically at the time of recovery. Meteorites are commonly cut, sliced or sometimes broken thus reducing the size of the main mass and the resulting largest specimen is called the "largest known mass". Click on Term to Read More, courtesy of Luc Labenne.