EL3
(ELb3/4 in Weyrauch et al., 2018)
Fell October 7, 2008
20° 43.04′ N., 32° 30.58′ E. In 2008, October 6 at 5:46 A.M., asteroid 2008 TC3 fell to Earth in northern Sudan. See the Almahata Sitta webpage for the complete story of the discovery of 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, results of the consortium analyses, and new models for the petrogenetic history of the ureilite 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..
ENSTATITE CHONDRITEType of meteorite high in the mineral enstatite and also referred to as E-chondrites. Although they contain substantial amounts of Fe, it is in the form of Ni-Fe metal or sulfide rather than as oxides in silicates. Their highly reduced nature indicates that they formed in an area of the SUBGROUPS Weyrauch et al., 2018 |
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EHa | EHb | ELa | ELb | |
Troilite | Cr <2 wt% | Cr >2 wt% | Cr <2 wt% | Cr >2 wt% |
(Mn,Mg,Fe)S | Fe <20 wt% | Fe >20 wt% | Fe <20 wt% | Fe >20 wt% |
Daubréelite | Abundant | Missing | Abundant | Missing |
Kamacite | Ni <6.5 wt% | Ni >6.5 wt% | Ni <6.5 wt% | Ni >6.5 wt% |
A few other E chondrites with intermediate mineralogy have also been identified, including LAP 031220 (EH4), QUE 94204 (EH7), Y-793225 (E-an), LEW 87223 (E-an), and PCA 91020 (possibly related to LEW 87223). Studies have determined that these meteorites were not derived from the EH or EL source through any metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. processes, and some or all of them could represent separate E chondrite asteroids. The revised E chondrite classification scheme of Weyrauch et al. (2018) including selected examples from their 80-sample study can be found here. It was determined that MS-MU-002 is a member of the ELb subgroup.
Petrographic and isotopic evidence indicate that the EL parent body accreted hot 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 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 components that were formed through repeated nebular condensation processes rather than by impact-heating events on a parent body (Weisberg et al., 2013). Observations consistent with a nebular condensation origin include the absence of shock-induced features, the lack of high-pressure polymorphs, the presence of metal–sinoite–oldhamite–graphiteOpaque form of carbon (C) found in some iron and ordinary chondrites and in ureilite meteorites. Each C atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, α (hexagonal) and β (rhombohedral), have assemblages composed of crystalline sinoite and poorly graphitized carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*., and the pristine texture of discrete chondrules and metal nodules, while the isotopic inventory is inconsistent with a large-scale impact-heating event. A high abundance of metal in the final agglomerationProcess of collecting in a jumbled cluster. In relation to meteorites, agglomeration refers to the early accretion of chondrules, refractory inclusions and silicate matrix material to form chondritic clusters. is also expected with the presumed nebular condensation sequence. Exclusive of the primary ureilite components, there was a broad diversity of lithologic types present in 2008 TC3, constituting <30% of all material recovered. However, with the vast bulk of 2008 TC3 thought to have been lost as fine dust (≥99.9% of the estimated 42–83 ton pre-atmospheric mass), the bulk asteroid was likely composed of fine-grained, highly porous, and weakly consolidated ureilitic matrix material, consistent with the reflectance spectra obtained for the asteroid (Goodrich et al., 2015). Examples of some of the diverse samples that have been recovered are listed below (Bischoff et al., 2010, 2015, 2016, 2018; Horstmann and Bischoff, 2010, 2014; Hoffmann et al., 2016):- ultrafine- to fine-grained ureilites (representing numerous lithologies with varying olivine compositions): MS-185 (ultrafine-grained), MS-MU-001, -018 (high shock, metal–sulfide-rich), -025 (high shock), -027 (high shock), -030 (high shock, metal–sulfide-rich), -032 (high shock, metal–sulfide-rich), -033 (high shock, metal–sulfide-rich), -040 (high shock), -045 (high shock)
- coarse-grained ureilites (representing numerous lithologies with varying olivine compositions: MS-MU-005, -006, -008, -010, -014 (very coarse), -016, -017, -020, -022, -034, -037, -038
- variable grain-sized ureilite breccias: MS-25, -205, -190; MS-MU-004, -021, -028, -042
- highly porous ureilitic (matrix) material: MS-168
- enstatite chondrites (36 representing numerous different enstatite chondrites): EH3 (MS-14), EH4/5 (MS-192, MS-MU-009), EH5 (MS-MU-041, -044), EL3 (MS-1, -17, -177, MS-MU-002, -023, -031), EL3/4 + melt (MS-17, MS-MU-039 [+ melt]), EL3–5 (MS-179), EL4 (MS-MU-029), EL4/5 (MS-192, MS-MU-009), EL5 (MS-196), EL5/6 (MS-7), EL6 (MS-150, MS-MU-007, -015, -024, -026), EL breccias (MS-MU-003), and both EL and EH (MS-155) shock-darkened, impact-melt rocks or impact-melt breccias
- ordinary chondrites: H4 (MS-MU-043), H5 (AhS 25, MS-151 [shock-darkened]), H5/6 (MS-11, with compositional discordance), L4 (AhS A100), LL4/5 (MS-197), H5-an (MS-MU-013)
- unique chondrite: MS-CH, type 3.8 [± 0.1], has petrographic and isotopic affinities to R-chondrites, but is mineralogically anomalous
- Bencubbin-like 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: MS-181, a 58.6 g chondrule-like clastA mineral or rock fragment embedded in another rock. containing metal globules and silicates in a 60:40 ratio, having an O-isotopic composition consistent with bencubbinites
- C2 carbonaceous chondrite: AhS 202 (photo; Fioretti et al., 2017, #1846)
- C1 carbonaceous chondrite: AhS 91/91A and 671 (photo; Goodrich et al., 2018, #1321)
- niningerite-bearing, fine-grained ureilitic fragment (linking E chondrites): MS-20
- sulfide-metal assemblage in a fine-grained ureilitic fragment: MS-158, -166
- ungroupedModifying term used to describe meteorites that are mineralogically and/or chemically unique and defy classification into the group or sub-group they most closely resemble. Some examples include Ungrouped Achondrite (achondrite-ung), Ungrouped Chondrite (chondrite-ung), Ungrouped Iron (iron-ung), and Ungrouped Carbonaceous (C-ung). enstatite- and metal-rich achondriteAn achondrite is a type of stony meteorite whose precursor was of chondritic origin and experienced metamorphic and igneous processes. They have a planetary or differentiated asteroidal origin where the chondritic parent body reached a sufficient size that through heating due to radioactive decay of Al (aluminum isotope) and gravitational fragments: MS-MU-019 (characteristics similar to NWA 8173/10271); MS-MU-036 (similar to MS-MU-019 and Itqiy [Bischoff et al., 2016]); AhS 38 (similar to MS-MU-019 and Itqiy but contains olivine [Goodrich et al., 2018]); AhS 60 (possible E IMR analogous to Portales Valley [Goodrich et al., 2018])
- the first known plagioclase-bearing olivine–augiteHigh-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. ureilite lithology: MS-MU-012
- trachyandesitic clasts: 1) MS-MU-011 (view 1), MS-MU-011 (view 2), sample ALM-A; plagioclase-enriched (~70 vol%) with pockets of gemmy olivine (photo courtesy of Stephan Decker), likely sampling the UPB 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 (or possibly an alkali- and water-rich localized melt pocket); calculated Ar–Ar age of ~4.556 b.y. and Pb–Pb age of ~4.562 b.y. (Bischoff et al., 2013, 2014; Delaney et al., 2015; Turrin et al., 2015; Amelin et al., 2015); 2) MS-MU-035; anorthoclase and/or plagioclase-enriched (~65 vol%) (Bischoff et al., 2016)
Special thanks to Siegfried Haberer and Stephan Decker for providing specimens of this special meteorite and many of its xenolithic inclusions to the scientific and collector communities. The photo of MS-MU-002 shown above is a 0.350 g full slice. The photo below shows the 3.00 g 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"..
Photo courtesy of Stephan Decker—Meteorite Shop and Museum