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
Found February 13, 2004 21° 04′ 31.6′ N., 57° 08′ 49.3′ E. During an expedition in Adam County, Oman, Rainer and Claudia Bartoschewitz found 64 fragments of a single 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 lying on a limestoneA common form of calcium carbonate (CaCO3). Other common forms of CaCO3 include chalk and marble. gravel plateau all within a distance of 10 meters (Bartoschewitz et al., 2005). The total weight of the constituted meteorite was 1.796 kg. The classification of SaU 290 was initially considered to be an anomalous E chondrite microbreccia with a weathering grade of W2, but the O-isotope composition of Sayh al Uhaymir 290 plots within 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 field, distinguishing it as a member of this very rare carbonaceous group.
The microstructure and microchemistry of a variety of FeNi-metal condensateIn the solar nebula, product of a chemical condensation reaction where a mineral phase precipitates (condenses) directly from a cooling vapor. particles from CH 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 were examined by Goldstein et al. (2005). A portion of the 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 particles were found to be zoned, with cores that are enriched in Ni and Co and depleted in P, Cr, and Fe. Other particles are unzoned and homogeneous, possibly reflecting diffusive equilibration during an extended period within the hot gas, a period of longer duration than that experienced by zoned particles. Ni-rich precipitates occur in a portion of both of these condensate types. In addition, a high-Ni metal grain identified as tetrataenite has been found. A silica-rich component similar to that observed in other CH chondrites was also identified (Zhang et al., 2007). CH-chondrite components originated from both highly reducingOxidation 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 and highly oxidizingOxidation 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 environments, constituting more than a single reservoir (Kimura et al., 2011).
A large N gas content has been found in SaU 290, residing in at least four components (Murty et al., 2007). The heavy N component (δ15N) is present in the same abundance as in other CH chondrites. Several carrier phases for the δ15N have been identified, including C–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 aggregates, FeNi-metal+Fe–Cr-sulfide, Si-rich metal+FeS, and in hydrated areas; however, it is believed that a single carrier, the C–silicate aggregates, was the original δ15N source prior to its redistribution into metallic phases during a quick nebular heating event (Sugiura and Zashu, 2001). 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 one or more chondritic objects. These hydrated clasts were agglomerated onto the Bencubbin 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. during its initial accretionary stages. The lower abundance of δ15N located within the hydrated areas is thought by some investigators to be the product of mixing of normal N and δ15N on the parent body. The presence of a carrier phase having a low abundance of δ15N has been seen in experiments, but has not yet been identified (Murty et al., 2007).
Based on a noble gasElement 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. studies at the University of Tokyo (J. Park, K. Nagao, and R. Okazaki), SaU 290 was shown to contain the highest solar noble gas abundances among CH group members. The He and Ne isotopic ratios in SaU 290 are consistent with solar values. A 21Ne-based CRE age has been established at 1.2 m.y. The average Δ17O value of –2.2 (±0.6‰) is nearly identical to the values in most CH, CB, and CH/CB magnesian 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 andchondrulesRoughly 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, indicating their likely formation from a common reservoir resulting from a single impact event (Nakashima et al., 2011). Given the range of O-isotopic values in those cryptocrystalline chondrules having anomalous values, it is proposed that they might have formed along with the type-I porphyritic chondrules.
A complete mineralogical inventory of the 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 and Al-rich chondrules present in SaU 290 has been prepared by Zhang and Hsu (2009). The 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 content of SaU 290 reflects the low abundance (0.1 vol%) and relatively small size (ave. ~40 µm) typical for other CH chondrites, but unlike those from other 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 groups. The small CAI sizes are thought to be the result of either a nebular sorting mechanism or a mechanism which controlled the growth rates. The CH group 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 are unique in composition from those of other carbonaceous chondrite groups and exhibit a highly refractory nature experiencing higher solar nebular peak temperatures of 1386–1074°C. They consist primarily of 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. and grossiteCalcium aluminate, CaAl4O7, first found in metamorphosed Israeli limestone and recently in CAIs in CV3 and CR-CH-CB carbonaceous chondrites., along with 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, spinelMg-Al oxide, MgAl2O4, found in CAIs., fassaite, and anorthiteRare compositional variety of plagioclase and the calcium end-member of the plagioclase feldspar mineral series with the formula CaAl2Si2O8. Anorthite is found in mafic igneous rocks such as anorthosite. Anorthite is abundant on the Moon and in lunar meteorites. However, anorthite is very rare on Earth since it weathers rapidly, and various combinations thereof. While some CAIs exhibit igneous features consistent with crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. from melt droplets, others have a layered texture indicative of nebular gas–solid condensation. An ultrarefractory inclusionFragment of foreign (xeno-) material enclosed within the primary matrix of a rock or meteorite. was identified in SaU 290 by Zhang et al. (2015), which is composed of such ultrarefractory phases as panguite, davisite, and Sc-rich anosovite, together with the more typical refractory phases spinel, anorthite, 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. This ultrarefractory CAI is depleted in 16O, which attests to its formation in the outer region of the protoplanetary diskFlattened and rotating disk of dense gas and dust/solids orbiting a young star from which planets can eventually form. where isotopic self-shielding during UV photolysis of CO preferentially produces an 16O-poor gas (Krot et al., 2009).
In addition, rare amoeboid olivine aggregatesMillimeter sized, fine-grained inclusions present to a few volume-percent in most carbonaceous chondrites. They can be round but can also be irregularly shaped like an amoeba (thus the name amoeboid). They are forsterite (Mg-rich olivine) and Ca-Al-Ti mineral aggregates. The most characteristic texture of AOAs is an anorthite core (sometimes (AOAs) composed of olivineGroup 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, Al-diopside, and anorthite have been identified in CH chondrites (Krot et al., 2014). These are texturally and mineralogically similar to AOAs in other carbonaceous chondrite groups that were formed as nebular condensates during the earliest stages of Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. history. A suite of Al-rich chondrules compositionally unique to those of other carbonaceous chondrite groups have also been documented. These are likely products of melted precursor material derived from both CAIs and ferromagnesian chondrules. The study presented evidence for low degrees of both thermal metamorphism and aqueous alteration on the CH parent body, leaving the inclusions in a pristine state and reflecting the nebular conditions in which they were formed.
Further information about the CH group can be found on the Acfer 214 page. The specimen of SaU 290 pictured above is a 2.88 g partial end section with an unpolished cut face. The photo below shows the ~200 g fragment from which the above piece was cut.
Photo courtesy of S. Turecki
For additional information on CH chondrite petrogenesis, read the PSRD article by G. Jeffrey Taylor: ‘The Oldest Metal in the Solar System‘, Sep 2000.