Martian Igneous stony meteorite with a Martian origin consisting mainly of plagioclase (or a shocked glass of plagioclase composition) and pyroxene. They are the most abundant type of SNC meteorites and the type member is the Shergotty meteorite, which fell in India in 1865. Shergottites are igneous rocks of volcanic or
(depleted, permafric, Oxidation 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 photos for a magnified view Found May 1, 1998
27° 21.16′ N., 16° 12.04′ E. Dar al Gani 476, also known as ‘Lucky 13’, is an olivine–orthopyroxene-phyric shergottite that was found in the Libyan Sahara Desert by an international team. The brown, loaf-shaped mass measuring ~ 15 × 10 cm and weighing 2,015 g was analyzed and classified at Germany’s Max-Planck-Institut für Chemie in Mainz; this is quite appropriate since this institute also developed the APXS instrument used during the Mars Pathfinder Mission aboard the Sojourner Rover to analyze surface rock compositions.
Several other olivine-bearing Igneous stony meteorite with a Martian origin consisting mainly of plagioclase (or a shocked glass of plagioclase composition) and pyroxene. They are the most abundant type of SNC meteorites and the type member is the Shergotty meteorite, which fell in India in 1865. Shergottites are igneous rocks of volcanic or were recovered in the same general area as DaG 476, including DaG 489, 670, 735, 876, 975, and 1037 (weighing 2,146 g, 1,619 g, 588 g, 6.2 g, 27.55 g, and 4,012.43 g respectively). Petrographic, mineralogic, textural, and shock features, as well as Element 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. and Radioactive isotope - Atomic nuclide that decays radioactively . abundances, are indistinguishable from those of DaG 476, and all of these masses are likely paired. After many tens of thousands of years of desert exposure (40–140 t.y.), DaG 476 has completely lost its Melted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of 4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below. and developed cracks and veins that are filled with Mineral or compound containing carbon and oxygen (i.e. calcium carbonate, CaCO3, calcite). and other terrestrial weathering products. Although likely falling at the same time, DaG 670 is much more highly weathered than DaG 476, while on the other hand, DaG 735 has experienced significantly less weathering than DaG 476 in exhibiting only µm-wide calcite veins. DaG 735 was actually the first of the four masses to be found, having been recovered during the winter of 1997/98.
Dar al Gani 476 contains an unusually high abundance (as high as 24 vol%) of zoned Group of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion megacrysts up to 5 mm in size. It also contains a low abundance of Orthorhombic, low-Ca pyroxene common in chondrites. Its compositional range runs from all Mg-rich enstatite, MgSiO3 to Fe-rich ferrosilite, FeSiO3. These end-members form an almost complete solid solution where Mg2+ substitutes for Fe2+ up to about 90 mol. % and Ca substitutes no more than ~5 mol. % (higher Ca2+ contents occur megacrysts up to ~0.3 mm in size, as well as orthopyroxene cores in others, similar to the larger orthopyroxene grains present in the ol–opx shergottites NWA 1195 and NWA 2046 (Irving et al., 2004, 2005). The high-magnesian olivine megacrysts, which contain unusual chromium-pyroxene inclusions, are generally considered to be phenocrysts derived from an olivine-saturated parent Molten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava.. They are embedded in a fine-grained groundmass composed mostly of Ca-poor Low-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, found as a major mineral in eucrites and shergottites. In order to be considered pigeonite, the clinopyroxene must contain 5 to 20 mol % of calcium (Wo5 - 20). Chondrites of petrologic types 4 and below contain significant low-Ca clinopyroxene. During metamorphism to higher temperatures, all existing and feldspathic glass, along with minor Ca-rich High-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, that occurs in many igneous rocks, particularly those of basaltic composition. In order to be considered augite, the clinopyroxene must contain 20 to 45 mol % of calcium (Wo20 - 45). An important and unique Martian meteorite is NWA 8159, that has been classified as an augite basalt.. In other studies (Koizumi et al., 2003), it was concluded that the olivine megacrysts are actually xenocrysts that crystallized within an Fe-rich melt through A crystallization process in which minerals crystallizing from a magma are isolated from contact with the liquid. It is a key process in the formation of igneous rocks during the process of magmatic differentiation. Also known as crystal fractionation., resulting in zoning from Fo76 to Fo58. Thereafter, these xenocrysts were entrained within an Mg-rich melt, cooling rapidly to preserve the olivine zoning, and eventually forming the groundmass.
Dar al Gani 476 shows close petrographic and mineralogical similarities to the shergottites EETA79001A, LAR 12095/240, SaU 005, NWA 1068, Dhofar 019, Y-980459, NWA 1195, NWA 2046, and others more recently found, all of which contain an abundance of inclusion-bearing olivine megacrysts, and some or all of these meteorites may be launch paired (Mikouchi and Takenouchi, 2014). In addition, the Often abbreviated as “REE”, these 16 elements include (preceded by their atomic numbers): 21 scandium (Sc), 39 Yttrium (Y) and the 14 elements that comprise the lanthanides excluding 61 Promethium, an extremely rare and radioactive element. These elements show closely related geochemical behaviors associated with their filled 4f atomic orbital. pattern (LREE-depleted) and Sm–Nd systematics imply that a close association once existed with the source melt of the basaltic shergottite QUE 94201, as well as to Nakhla and Chassigny. However, the less evolved, highly One of the two broad categories of silicate minerals, the other being felsic, based on its magnesium (Mg) and/or iron (Fe) content. Mafic indicates silicate minerals that are predominantly comprised of Mg and/or Fe.The term is derived from those major constituents: Magnesium + Ferrum (Latin for iron) + ic (having compositions of olivine, A class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category., Brownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups., and Ti-Fe oxide, TiFeO3, found in achondrites, lunar mare basalts, and shergottites. Ilmenite forms as a primary mineral in mafic igneous rocks. It crystallizes relatively early out of a magma before most of the other minerals, and as a result, the heavier crystals of ilmenite precipitate to the bottom of the magma present in DaG 476 compared to QUE 94201 suggest that the parent magma of DaG 476 experienced a late episode of fractional Physical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. (Borg et al., 2002). It was also determined that the higher Rb/Sr ratio of the QUE 94201 magma could be accounted for by the presence of an amphibole component. This amphibole is chlorine-rich and water-poor, reflecting the Substances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). content of the source magma (Filiberto and Treiman, 2009). In a contrasting study, McCubbin et al. (2009) found that kaersutite and Ti-biotite in Chassigny melt inclusions contain higher abundances of water than previously measured, a value which correlates to a parental source magma water content of ~460–840 Parts per million (106). (0.5–0.8 wt%), while lower abundances of Cl and F were observed.
The conditions under which DaG 476 crystallized were also more Oxidation 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 than those of other basaltic shergottites, and it is one of the most magnesian shergottites (Fo76) of the olivine-bearing subgroup, with only Y-980459, NWA 2046, and NWA 1195 having more magnesian olivines. Overall, its mineralogy and bulk chemistry indicate that it is a distinct shergottite intermediate in composition between the basaltic and poikilitic (formerly ‘lherzolitic’) subgroups. A xenolith-bearing Basalt is the most common extrusive igneous rock on the terrestrial planets. For example, more than 90% of all volcanic rock on Earth is basalt. The term basalt is applied to most low viscosity dark silicate lavas, regardless of composition. Basalt is a mafic, extrusive and fine grained igneous rock found on Kauai, Hawaii may be a terrestrial analog of this shergottite subgroup. The Mars Exploration Rover Spirit, which landed inside Gusev Bowl-like depression ("crater" means "cup" in Latin) on the surface of a planet, moon, or asteroid. Craters range in size from a few centimeters to over 1,000 km across, and are mostly caused by impact or by volcanic activity, though some are due to cryovolcanism., discovered several picritic basaltic rocks, subsequently named Adirondack, Humphrey, and Mazatzal. Analyses of these Adirondack-class basalts revealed they are fine-grained rocks with a Also referred to as the plagioclase feldspar series. Plagioclase is a common rock-forming series of feldspar minerals containing a continuous solid solution of calcium and sodium: (Na1-x,Cax)(Alx+1,Si1-x)Si2O8 where x = 0 to 1. The Ca-rich end-member is called anorthite (pure anorthite has formula: CaAl2Si2O8) and the Na-rich end-member is albite and pyroxene composition, containing dark megacrysts of ferroan olivine, very similar to DaG 476 (McSween et al., 2004). Experimental work on a synthetic analog of the Adirondack-class basalts by Filiberto et al. (2008) indicates that these rocks probably do not represent a primary mantle-derived hydrous melt, but rather, the magma likely rose and pooled into a shallow chamber within the Outermost 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 where it underwent Concentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process..
The isotopic systematics (i.e., Sm–Nd, Rb–Sr, Lu–Hf, Hf–W) of DaG 476 indicate that A process by which a generally homogeneous chondritic body containing mostly metal, silicates and sulfides will melt and form distinct (differentiated) layers of different densities. When the melting process continues for a long enough period of time, the once chondritic body will re-partition into layers of different composition including from a chondritic source occurred ~4.513 b.y. ago, and also attest to a young crystallization age of 474 (±11) m.y. Based on the Fe–Mg zoning profile of olivine, DaG 476 experienced rapid cooling calculated at 0.089°C/hr, corresponding to a burial depth during crystallization of several meters (Miyamoto et al., 2009). By some accounts, DaG 476 was formed through a high-degree of An igneous process whereby rocks melt and the resulting magma is comprised of the remaining partially melted rock (sometimes called restite) and a liquid whose composition differs from the original rock. Partial melting occurs because nearly all rocks are made up of different minerals, each of which has a different melting of a primitive lherzolite-like (olivine-saturated) source rock mixed with another martian rock. This was followed by the segregation of a melt containing unmelted phases of olivine, A 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)., and chromite. A residue containing a fraction of these unmelted phases was removed from this ‘crystal mush’, leaving behind the fraction that would eventually form DaG 476. An alternative petrogenesis was outlined by Goodrich (2003) and Koizumi et al. (2004) in which a small fraction (a few percent) of zoned, xenocrystic chromite and magnesian olivine and pyroxene, which were the products of fractional crystallization, became emplaced within a pyroxene groundmass phase formed through a Igneous rock composed of crystals that have grown and accumulated (often by gravitational settling) in a cooling magma chamber. process, in combination with the loss of a residual fractionated melt (see also Koizumi et al., 2003, above). A crystallization history was constructed by Mikouchi and Takenouchi (2014) for LAR 12095 and its likely launch pairings such as DaG 476. They suggest that crystallization occurred initially under slow cooling conditions from temperatures of ~1400°C down to ~1250°C, followed by a rapid cooling stage of 0.03–3°C/hour which preserved the chemical zoning in silicates.
The texture of the olivine phenocrysts and pyroxene crystals are indicative of flow alignment within an extruded Hot molten or semifluid rock derived from a volcano or surface fissure from a differentiated and magmatically active parent body. flow near the surface. Features indicative of high shock include olivine In 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. staining, twinning of clinopyroxene, mosaicism of olivine, plagioclase converted to feldspathic glass, and abundant impact-melt veins and pockets, all which correspond to a A petrographic assessment, using features observed in minerals grains, of the degree to which a meteorite has undergone shock metamorphism. The highest stage observed in 25% of the indicator grains is used to determine the stage. Also called "shock level". of 44–56 GPa; it was demonstrated that these features were formed at the time of ejection. A shock-melt vein identified in the paired DaG 735 provides evidence for olivine dissociation adjacent to the vein that has resulted in a granular texture consisting of magnesiowüstite + Term 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; temperatures of at least 700°C were required to produce this phase (Miyahara et al., 2011). Both cooling models and experimental results were utilized to constrain the cooling history of melt veins and pockets in DaG 476 and other shergottites, demonstrating a rate of ~0.2°C/second over time intervals of seconds to minutes, depending on the size and shape of the melt features and their proximity to other melt features (Walton et al., 2006; Shaw and Walton, 2013). Based on these data, a pre-atmospheric diameter of ~19 cm was estimated for the DaG 476 Small rocky or metallic object in orbit around the Sun (or another star)., while that estimated by Nishiizumi et al. (2011) based on cosmogenic nuclides was ~30–40 cm.
Similar to other highly shocked martian meteorites, DaG 476 contains a significant concentration of martian atmospheric Ar within the melt pockets (ave. 4.6 Parts per billion (109).), with a minor component present within shock veins (ave. 1.3 ppb). The favored interpretation of the existence of this trapped gas component within the melt pockets calls for the initial introduction of martian atmospheric gas into pre-existing cracks and pores. During an impact-ejection event, probably that which launched the rock to Earth, a Abrupt perturbation in the temperature, pressure and density of a solid, liquid or gas, that propagates faster than the speed of sound. was generated that passed through a decimeter-sized meteoroid causing sudden decompression, followed by an ensuing pressure release. Thereafter, bubbles were created within localized, in situ, mm-sized melt pockets containing superheated melt, which then cooled at rapid rates over a short time interval on the order of seconds to minutes (Walton and Herd, 2007). Thereafter, as pressures reached Term used to describe physical or chemical stasis. Physical equilibrium may be divided into two types: static and dynamic. Static equilibrium occurs when the components of forces and torques acting in one direction are balanced by components of forces and torques acting in the opposite direction. A system in static, the trapped atmospheric gases migrated into the vesicles of the melt phase from the surrounding cracks and pores (Walton et al., 2007). Studies by Shaw and Walton (2013) revealed how such implanted martian atmospheric Element 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. could experience diffusive loss (Xe more rapidly than Ar) in the large melt pockets with long cooling intervals, resulting in a small increase in the Ar/Xe ratio.
Comparisons with Viking inert gas measurements, as well as results from chemical, mineralogical, petrographic, and Element that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only isotopic studies, clearly identify DaG 476 as martian. Combining the 21Ne-based CRE age of 1.05 (±0.1) m.y. and the calculated terrestrial age of 60 (±20) t.y., a Mars ejection 1.1 (±0.1) m.y. ago is derived. Similarly, Park et al. (2003) calculated a terrestrial age for DaG 476 of 140 t.y., with an ejection age of 1.08 m.y. As well, Nishiizumi et al. (2011) calculated a terrestrial age for DaG 476 of 60 (±20) t.y. and a CRE age of 0.95 (±0.1) m.y., resulting in an ejection age of 1.0 (±0.1) m.y. This ejection age is indistinguishable from that of at least 7 other depleted olivine-phyric shergottite falls (e.g., SaU 005 and Tissint), evidently representing a common ejection event on Mars. Cosmic ray exposure ages have now been determined for many martian meteorites, and Mahajan (2015) compiled a chart based on the reported CRE ages for 53 of them. He concluded that together these 53 meteorites represent 10 distinct impact events which occurred 0.92 m.y., 2.12 m.y., 2.77 m.y., 4.05 m.y., 7.3 m.y., 9.6 m.y., 11.07 m.y., 12.27 m.y., 15 m.y., and 16.73 m.y.—see his chart here. It was argued that DaG 476 was launched from Mars during the 0.92 m.y.-old impact event. In a subsequent review based on multiple criteria, Irving et al. (2017 [#2068]) made a new determination of the number of separate launch events associated with the known (101 at the time of their study) martian meteorites. They speculate that the number could be as few as twenty, and suggest that the DaG 476 pairing group and at least 18 other depleted (predominantly olivine-phyric) shergottites were ejected 1.1 m.y. ago in a common impact event unique from the others. Notably, the composite shergottite EETA79001 has one of the youngest ejection ages of any martian sample at 0.73 (±0.15) m.y., and while Mahajan (2015) included it with the 0.92 m.y.-old impact event, Irving et al. (2017) argue that it represents a unique ejection event.
The olivine-bearing shergottite, Sayh al Uhaymir 005, was recovered in Oman in 1999. Together with several probably paired masses recovered later, it has a total combined weight of ~9.9 kg. SaU 005 shows very close similarities to DaG 476 in bulk chemical composition and texture, but it shows mineralogical evidence of having experienced slower cooling rates, exhibiting a microgabbroic texture. Noble gas and The age of an object determined by the proportions of its original radioactive elements at the time of object's formation and the decay products of those elements at some period in the future. data place the cosmic-ray Time interval that a meteoroid was an independent body in space. In other words, the time between when a meteoroid was broken off its parent body and its arrival on Earth as a meteorite - also known simply as the "exposure age." It can be estimated from the observed effects at ~0.81 m.y. (Park et al., 2003), indicating an ejection from Mars slightly later than that calculated for DaG 476. The pre-atmospheric diameter of SaU 005 was calculated to have been at least 54 cm, corresponding to a mass of ~270 kg. Compared to DaG 476, SaU 005 has experienced less weathering, with a calculated terrestrial age of only ~13 t.y. It has retained a partial Process in which two lighter atomic nuclei combine to form a heavier atomic nucleus. Very high temperatures are normally required in order for atomic nuclei to collide with sufficient energy to overcome the Coulomb barrier (their mutual electrostatic repulsions). Fusion that occurs under high-temperature conditions is called thermonuclear fusion. Fusion crust and exhibits few terrestrial alteration products. Although their respective terrestrial ages indicate they are not from the same Meteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If, SaU 005 and Dag 476 are likely comagmatic rocks from the same igneous region on Mars.
Also in 1999, two paired stones totaling 698 g were found in a collection of meteorites in Los Angeles, California. This basaltic shergottite is one of the most evolved martian meteorites found to date, and it has been shown that similarities in Substance 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 composition, petrography, and Inorganic 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 chemistry to both NWA 2800 and Ksar Ghilane 002 shergottites suggest they may be launch-crater pairings to Los Angeles (Bunch et al., 2008; Llorca et al., 2013). Los Angeles crystallized in a lava flow or shallow intrusion, and experienced a slower cooling rate than most other shergottites, resulting in its very coarse-grained texture. A cosmic-ray exposure age of ~3.0 m.y. is similar to that of the basaltic shergottites KG 002, Shergotty, Zagami, QUE 94201, and others, suggesting a common ejection event for all.
Further recoveries of martian shergottites have continued, including the 1,056 g olivine-bearing shergottite found in Oman in January, 2000 named Dhofar 019. This Work 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 has features quite similar to those of DaG 476, including an abundance of olivine megacrysts. Although megacrysts in Dhofar 019 are less magnesian, it may share a common parental melt with DaG 476, with similarities to QUE 94201. However, in constrast to DaG 476, Dhofar 019 represents a fractionated restite. A 21Ne-based CRE age of ~20.7 m.y. has been calculated for Dhofar 019 (Park et al., 2003). This is one-third longer than any other Over 30 of the meteorites found on Earth almost certainly came from Mars (see http://www.imca.cc/mars/martian-meteorites.htm and http://www2.jpl.nasa.gov/snc/). All but one belongs to the group known as SNC meteorites, which includes the shergottites, nakhlites, and chassignites. SNC meteorites contain minerals that crystallized within the past 1.35 to 0.15 Ga, making them, and four times longer than any other shergottite—a CRE age at the theoretical limit of the calculated delivery time of material to Earth from Mars.
Among an already staggering number of recent martian shergottite finds, new shergottites continue to be found, e.g., NWA 480/1460, NWA 856, NWA 1195, NWA 1068 (and pairings), NWA 2046, NWA 1669, NWA 2626, NWA 3171, and others from Morocco and neighboring countries, the highly-ferroan Dhofar 378 found in Oman, and the Antarctic Y-980459, the only martian meteorite that lacks plagioclase. Northwest Africa 1068 and Y-980459 have an olivine-phyric texture, while NWA 1195, NWA 2626, and NWA 2046 join DaG 476 as a newly recognized grouping of olivine–orthopyroxene-phyric shergottites. In addition, the poikilitic (formerly ‘lherzolitic’) shergottite NWA 1950 was discovered, as well as the unique plagioclase–olivine-clinopyroxenite, NWA 2646, related to the martian poikilitic shergottite group.
Although ALH 84001 is an A rock composed primarily of orthopyroxene. Non-terrestrial orthopyoxenites include diogenites and a single martian meteorite, ALH 84001, that was found in the Allan Hills region of Antarctica in 1984. ALH 84001 is a cumulate rock consisting of 97% coarse-grained, Mg-rich orthopyroxene, with small amounts of plagioclase, chromite, and carbonate. It, and as such was characterized by the Planetary Chemistry Laboratory at Washington University as a subgroup of the nakhlites, its parental source magma has a composition that is consistent with the same mixtures of depleted and enriched REE end-member components that are used in a geochemical classification of the shergottites (Lapen et al., 2012). It was determined that the source magma of ALH 84001 contained a higher proportion of the enriched REE component than all other shergottites studied thus far. Therefore, ALH 84001 may be most appropriately classified as a subgroup of the shergottites.
Remarkably, two separate but similar clasts of an alkaline-enriched lithology were found in the Kaidun meteorite—one that was melted in situ and the other unaffected by impact forces. Based on mineralogical and textural characteristics, they have been identified as possible basaltic shergottite material (Ivanov et al., 2001, 2003). In a further study of these two clasts (Ivanov and Zolensky, 2003), it was proposed that the circumstances of repeat encounters with the Kaidun CR-like host object of an extremely rare alkaline-rich rock, necessarily derived from a large differentiated body, was consistent with a characterization of Kaidun as the martian moon Phobos. However, Ziegler et al. (2012), studying clasts of differentiated material in Kaidun, found Δ17O values inconsistent with those of martian meteorites and which don’t plot with any known meteorite material on an oxygen three-isotope diagram. Notably, numerous fragments of another alkali-rich meteorite have been found in the Sahara—NWA 7034/7533. Studies have determined that the meteorite was likely part of an extensive impact-melt-breccia lens from the near-surface crust of Mars that experienced subsequent impact gardening and mixing with aeolian-distributed, siderophile-enriched meteoritic contaminates contained in soils and dust. This martian meteorite has a texture/structure that has been likened to that of a One type of meteorite in the HED (Howardite, Eucrite, Diogenite) achondrite group. Howardites are named after the English chemist Edward Howard (1774-1816), one of the pioneers of meteoritics. Consisting mostly of eucritic and diogenitic clasts and fragments, howardites are polymict breccias. However, they can also contain dark clasts of carbonaceous.
As of the beginning of the year 2013, approximately 65 terrestrially unpaired martian meteorites were known, all of which may represent less than half a dozen common ejection events on Mars. The specimen pictured above is a 0.7 g polished partial slice in which dark olivine xenocrysts are seen embedded throughout the greenish pyroxene Fine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents.. The photo below shows the DaG 476 meteorite in situ.
∗ Recent geochemical research on the martian basalts has led to new petrogenetic models and classification schemes.read more >>