Systematics: Enstatite Chondrites – Subgroup Classification
PART I: CHONDRITES, METACHONDRITES
PART II: PRIMITIVE ACHONDRITES, ACHONDRITES, STONY-IRONS, IRONS
PART III: MARTIAN METEORITES—GEOCHEMICAL CLASSIFICATION
PART IV: DIOGENITES—IUGS TAXONOMY
ENSTATITE (E) CHONDRITES
Subgroup classification after Weyrauch et al., MAPS, vol. 53, #3, pp. 394–415 (2018)
‘Chemical variations of sulfides 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 in 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). chondrites—Introduction of a new classificationPositively charged ion. scheme’
| ENSTATITE 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 (4 subgroups plus 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)./anomalous members, based on 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 and chemical data [see below]) |
| ELa |
| ELa3 (e.g. AhS MS-189, MAC 88136 [3.8/3.9], MAC 02747 [3/4], QUE 94594) |
| ELa4 (e.g. DaG 734, Grein 002 [4/5]) |
| ELa5 (e.g. AhS MS-201, TIL 91714) |
| ELa6 (e.g. Atlanta, Danielï ¿ ½s Kuil, Hvittis, Khairpur, Neuschwanstein, NWA 3134, Pillistfer, Sahara 99456, Yilmia) |
| ELa7/impact-melt phase (e.g. Ilafegh 009 [7/MR]) |
| ELb |
| ELb3 (e.g. AhS MS-17 [3/4], AhS MS-164 [3/4], AhS MS-200 [3/4], AhS MS-MU-002 [3/4], AhS MS-MU-003 [3/4], AhS MS-MU-039 [3/4 + melt]) |
| ELb4 (e.g. Y-793246) |
| ELb5 (e.g. AhS MS-7 [5/6], AhS MS-196, RKPA80259) |
| ELb6 (e.g. AhS MS-52, AhS MS-79, AhS MS-150, AhS MS-159, AhS MS-172, AhS MS-174, AhS MS-D, AhS MS-MU-007, EET 90102, LEW 87119) |
| ELb7/impact-melt phase (no sample classified) |
| EHa |
| EHa3 (e.g. AhS MS-14, ALH 84206, GRO 95517, MIL 07028, Parsa, Qingzhen, Sah 97096 [3.1–3.4]) |
| EHa4 (e.g. EET 87746, EET 96135 [4/5], Indarch, MET 00636, PCA 82518, Y-74370) |
| EHa5 (e.g. St. Mark’s, QUE 93372) |
| EHa6 (no sample classified) |
| EHa7/impact melt phase (e.g. LAP 02225 [IMR]) |
| EHb |
| EHb3 (no sample classified) |
| EHb4 (e.g. Adhi Kot [or IMB]) |
| EHb5 (e.g. AhS MS-13, AhS MS-155, AhS MS-163, AhS MS-192, AhS MS-MU-041, AhS MS-MU-044, LEW 88180, Saint-Sauveur [IMB]) |
| EHb6 (e.g. Y-8404 and pairings [or IMB/MR], Y-980211, Y-980223) |
| EHb7/impact melt phase (e.g. Abee [IMB]) |
| ENSTATITE CHONDRITES—NOT YET CLASSIFIED BY SUBGROUP |
| EL |
| EL3 (e.g. Kaidun IV, NWA 305, NWA 3132, NWA 2965 and pairings [3/6 IMB], QUE 93351) |
| EL4 (e.g. DaG 1031, FRO 03005, HaH 317, QUE 94368) |
| EL5 (e.g. Adrar Bous, NWA 1222, Tanezrouft 031) |
| EL6 (e.g. Eagle, Forrest 033) |
| EL7/impact-melt phase (e.g. Happy Canyon [MR], Y-980524 [IMB]) |
| EH |
| EH3 (e.g. Galim (b) [IMB], Hadley RilleLong narrow depression on the surface of the Moon; also called "sinuous rilles". Lunar rilles usually flow away from small pit structures and probably mark lava channels or collapsed lava tubes that formed during mare volcanism. In some cases, the lunar flows may have melted their way downwards into older [IM]) |
| EH4 (e.g. Bethune [4/5], Dhofar 1015, LAP 031220, Y-791810) |
| EH5 (e.g. A-881475, Kaidun-III, Oudiyat Sbaa) |
| EH6 (e.g. MIL 090846, NWA 6363, NWA 7976, NWA 8513 [IMB]) |
| EH7/impact melt phase (e.g. Itqiy [Meta-EH-anom or partial melt residue], NWA 2526 [similar to Itqiy], NWA 7324 [MR], NWA 10237 [MR], QUE 94204 [7], Y-82189 [IM], Y-8414 [IM]) |
| UNGROUPED E CHONDRITES |
| E-ung (e.g. LAP 031220 [4], LEW 87223 [3-anom], NWA 974 [6], PCA 91020 [3-anom; poss. rel. to LEW 87223], QUE 94204 [7], Y-793225 [6-anom]) |
Weyrauch et al. (2018) analyzed the mineral and chemical data from 80 enstatite chondrites representing both EH and EL groups and spanning the full range of petrologic types for each group. They found that a bimodality exists in each of these groups with respect to both the Cr content in troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites. and the Fe concentration in niningerite and alabanditeMagnesium sulfide found in aubrites and EL chondrites. Its formula is MnS. (endmembers of the [Mn,Mg,Fe] solid solutionCompositional variation resulting from the substitution of one ion or ionic compound for another ion or ionic compound in an isostructural material. This results in a mineral structure with specific atomic sites occupied by two or more ions or ionic groups in variable proportions. Solid solutions can be complete (with series present in EH and EL groups, respectively). In addition, both the presence or absence of daubréelite and the content of Ni in kamaciteMore common than taenite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Kamacite, α-(Fe,Ni), contains 4-7.5 wt% Ni, and forms large body-centered cubic crystals that appear like broad bands or beam-like structures on the etched surface of a meteorite; its name is derived from the Greek word were demonstrated to be consistent factors for the resolution of four distinct E 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 groups: EHa, EHb, ELa, and ELb (see table below).
| 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 |
||||
|---|---|---|---|---|
| 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.
PART I: CHONDRITES, METACHONDRITES
PART II: PRIMITIVE ACHONDRITES, ACHONDRITES, STONY-IRONS, IRONS
PART III: MARTIAN METEORITES—GEOCHEMICAL CLASSIFICATION
PART IV: DIOGENITES—IUGS TAXONOMY You must collect things for reasons you don’t yet understand.
Daniel J. Boorstin – Librarian of Congress
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