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Zag (B)

Achondrite, ungrouped
(brachinite-like)
standby for zag (b) photo
Found 1999
no coordinates recorded An oriented, fusion-crusted stone weighing 300 g was found near the site of the Zag meteorite fall in Morocco (see photo of main mass with flow lines at the RSPD website). Zag (b) is an unbrecciated achondrite rich in forsteritic olivine (68 vol%) that incorporates mm-sized orthopyroxene channels containing metal or sulfide or weathered metal inclusions. These orthopyroxene and opaque assemblages exhibit several features that indicate the occurrence of a late reduction process, and the Fe–Mn–Mg relations are also consistent with reduction processes on the brachinite parent body. Several methods for the reduction of primary olivine were reviewed by Goodrich et al., 2017), including its reaction with methane to form orthopyroxene + metal (Irving et al., 2013) and through its sulfurization by a S-rich fluid or gas to form orthopyroxene + sulfide (e.g., Singerling et al., 2013). Olivine and orthopyroxene exhibit variability in their distribution (Day et al., 2012). The oxygen isotope ratios plot close to those for Divnoe, NWA 4042, and the brachinites, although Zag (b) has undergone a more thorough reduction process.

Zag (b) shares very close similarities with Divnoe and the brachinites in Fe ratios and oxygen isotopic systematics. Moreover, the acapulcoites and lodranites fall on the same oxygen mixing line, and they have Fe–Mn–Mg features consistent with a close relationship to Zag (b), Divnoe, and the brachinites. All of these different meteorites likely formed in the same nebular region from common precursor material, with Zag (b) having an intermediate position between Divnoe and the ACA–LOD cluster. Because of its close relationship to Divnoe, and by extension, the brachinites, Zag (b) is sometimes conveniently included with the brachinites in classification studies. Further information about Zag (b) can be found in the abstract ‘Zag (b): A Ferroan Achondrite Intermediate Between Brachinites And Lodranites’ by Delaney et al., 31st LPSC, #1745 (2000).

On a newly compiled O-isotope diagram for brachinites and other planetary achondrites, published by Rumble III et al. (2008), Zag (b) has a Δ17O value that plots within a select grouping of brachinites including NWA 3151, NWA 595, and the ungrouped brachinite-like achondrite NWA 4042, and these investigators believe that Zag (b) should probably be lumped with the brachinites. However, through studies of highly siderophile element (HSE) abundances, and upon examining the metal-sulfide segregation processes, it was determined by Day et al. (2012) that Zag (b) and similar brachinite-like achondrites were not likely genetically related (i.e. from the same parent body) to brachinites, but rather, originated on similar volatile-rich, oxidized, chondritic precursor asteroids while experiencing similar petrologic processes during their formation history. Goodrich et al. (2017) determined that brachinites and brachinite-like achondrites have a distinct redox trend and a higher Fe/Mg ratio compared to all other primitive achondrites, consistent with formation in a similar nebula reservoir; therefore, they suggest that brachinites and brachinite-like achondrites be called the brachinite clan.

The measured HSE abundances are consistent with a partially melted parent body in which heating from short-lived radionuclides came to a halt before a core was fully formed. Studies of the fractionation trends for Zag (b) led Day and Warren (2015) to conclude that this meteorite might not have been a residue after partial melting, but instead represents a cumulate that incorporated a residual metallic melt with a high Pt/Os ratio; the ungrouped cumulate achondrite NWA 6704 and the brachinite-like cumulate achondrite MIL 090206 (and pairings) exhibit similar elevated Pt/Os ratios.

The specimen of Zag (b) shown above is a 2.2 g partial slice. A microscopic examination reveals the yellow-green olivine enclaves scattered throughout this meteorite.


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NWA 4042

Achondrite, ungrouped
(brachinite-like)
standby for nwa 4042 photo
Purchased 2003
no coordinates recorded

A single meteorite weighing 56.2 g was found in Western Sahara and subsequently purchased by S. Ralew in Midelt, Morocco; a search for further pairings have proven unsuccessful. This small stone was analyzed over an extended period at the Museum für Naturkunde, Berlin, Germany (A. Greshake) and the Planetary and Space Sciences Research Institute, The Open University, Milton Keynes, UK (I. Franchi and R. C. Greenwood). Northwest Africa 4042 is substantially composed of equigranular olivine crystals (~93.3 vol%), along with minor low-Ca pyroxene and accessory FeNi-metal, phyrrotite, and Mg–Al–Ti-chromite.

As a result of five test runs, the O-isotopic composition of NWA 4042 was determined to plot near several resolved fields—the aubrites, brachinites, and winonaites. Therefore, this meteorite was classified as an ungrouped achondrite. A subsequent O-isotopic analysis employing an acid leaching technique demonstrates that NWA 4042 plots within the brachinite field (Greenwood et al., 2007). A newly compiled O-isotope diagram for brachinites and other planetary achondrites, based on published data from Rumble III et al. (2008), demonstrates that NWA 4042 (Δ17O value of –0.177) plots within a select grouping of brachinites including NWA 3151, NWA 595, and Zag (b); these investigators believe that this meteorite should probably be lumped with the brachinites (see also this MetBull 90 oxygen three-isotope plot).

However, through studies of highly siderophile element (HSE) abundances, and upon examining the metal-sulfide segregation processes, it was determined by Day et al. (2012) that NWA 4042 and similar brachinite-like achondrites were not likely genetically related (i.e. from the same parent body) to brachinites, but rather, originated on similar volatile-rich, oxidized, chondritic precursor asteroids while experiencing similar petrologic processes during their formation history. Goodrich et al. (2017) determined that brachinites and brachinite-like achondrites have a distinct redox trend and a higher Fe/Mg ratio compared to all other primitive achondrites, consistent with formation in a similar nebula reservoir; therefore, they suggest that brachinites and brachinite-like achondrites be called the brachinite clan.

Northwest Africa 4042 shows evidence of very weak shock (S2), and a low degree of weathering (W2). The specimen of NWA 4042 shown above is a 0.63 g partial slice. The top photo shown below is the remaining 16.19 g main mass, and below that is a 40× magnified view of a cut section depicting a coarse-grained, recrystallized texture. standby for nwa 4042 photo
standby for nwa 4042 photo
Photos courtesy of Stefan Ralew—SR–Meteorite


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NWA 1500

Achondrite, ungrouped
(Brachinite-like)
(Ureilite [olivine-augite type] in MetBull 87)

standby for nwa 1500 photo
Purchased 2000
no coordinates recorded

A single, partially fusion-crusted stone weighing 3.3 kg was purchased in Zagora, Morocco. The meteorite was later sold to a dealer in Tucson, and then finally traded to R. Bartoschewitz in April 2002. This meteorite, which was designated NWA 1500, was initially analyzed and classified at the Max Planck Institut für Chemie in Germany as a plagioclase-bearing basaltic ureilite.

The presence of reverse-zoned reduction rims and the resulting grain boundary darkening in NWA 1500 olivines and their absence in other brachinites compelled some investigators to make an initial classification of NWA 1500 as a monomict ureilite. It also exhibited an equigranular texture and abundant triple junctions, and was composed mainly of coarse-grained olivine grains (~95 vol%) along with melt pockets and secondary veins containing a heterogeneous distibution of Ca-rich augite (2–3 vol%), chromite (0.6–1.6 vol%), plagioclase (0.7–1.8 vol%), andesine, and diopside. Other constituents include FeNi-metal, graphite (not found subsequently), lonsdaleite, and diamond. The high olivine fayalite content of Fa28 (as high as Fa35, Goodrich et al., 2006) initially distinguished this meteorite as potentially the most ferroan ureilite known (Bartoschewitz et al., 2003).

One of the most interesting components of this meteorite is the plagioclase grains. They occur as poikilitic grains measuring 0.5–3.0 mm across which enclose olivine and augite. This is consistent with an igneous association with olivine rather than an association through an impact-melting event. This plagioclase potentially represents the basaltic component of the UPB, which has heretofore only been studied in very small clasts from polymict ureilites, it could provide important information relating to the evolution of the UPB (Cohen and Goodrich, 2003).

Continued studies have shown that NWA 1500 is more similar to brachinites than any other group with respect to most of its petrographic, geochemical, and mineralogical features (Kita et al., 2009; Goodrich et al., 2011). Moreover, in contrast to ureilites, which show high equilibrium temperatures in the range of 1200–1300°C, the equilibrium temperature for NWA 1500 calculated by multiple methods is only 880°C (±70°C), inconsistent with having an origin on the ureilite parent body. The measured HSE abundances are consistent with a partially melted parent body in which heating from short-lived radionuclides came to a halt before a core was fully formed.

Initial oxygen-isotopic studies conducted by R. Clayton and T. Mayeda at the University of Chicago in 2003 demonstrated that NWA 1500 had a unique O-isotopic plot among the ureilites, forming an extention of the ureilite trend line. This initial O-isotope plot also fell on the border of the winonaite/IAB field near the lodranite/acapulcoite field, and was very close to the brachinite-like, primitive achondrite Divnoe. It did not fit the results expected for the isotopic fractionation of a basaltic partial melt, which called into question the exact nature of this meteorite. Subsequent highly precise O-isotopic analyses were conducted on NWA 1500 (Kita et al., 2009; Spicuzza et al., 2007; Greenwood et al., 2007). When plotted on an oxygen three-isotope diagram (courtesy of Achim Raphael), the O-isotope values (Δ17O = –0.811‰ [Miller, 2002]) are well removed from the ureilite trend line and plot within the brachinite field (along with Divnoe, NWA 595, and GRA 06128/9). This supports a genetic relationship (i.e., same parent body) with the brachinites.

A separate sample of NWA 1500 was studied by Mittlefehldt and Hudon (2004). They found a composition consisting of ~90 vol% coarse-grained olivine exhibiting a weak preferred alignment, with narrow reduction rims of magnesian pyroxene containing abundant Ni-free metal grains, causing silicate darkening. The remaining component, comprising coarse-grained augite and chromite with minor FeNi-metal, is almost totally lacking in plagioclase. They also found different Fe–Mn–Mg compositions than those determined in the initial study, values that plot well outside of ureilite ranges. Furthermore, the CaO and CrO contents in NWA 1500 olivine cores are significantly lower than, and the Wo content significantly higher than, normal ureilite trends. Moreover, in contrast to typical C contents in ureilites (7–66 mg/g), the C content in NWA 1500 was too low to measure, and no CO2 was released upon heating (Murty et al., 2007). Finally, as determined previously and since refined, the O-isotopic composition of NWA 1500 falls outside of the ureilite range and clearly within the brachinite field. For these reasons, they have suggested that NWA 1500 might be a unique, olivine-dominated, ultramafic rock containing trace plagioclase, and not a member of the ureilite group. They suggested that other primitive achondrites with similar textures (but with less ferroan compositions) such as brachinites, winonaites, and acapulcoites should be compared.

Goodrich et al. (2006, 2010) observed fine-grained assemblages of orthopyroxene and opaques lining various olivine grain boundaries nearly identical to those found in other brachinites. These assemblages exhibit several features that indicate the occurrence of a late reduction process, and the Fe–Mn–Mg relations are also consistent with reduction processes on the brachinite parent body. Several methods for the reduction of primary olivine were reviewed by Goodrich et al., 2017), including its reaction with methane to form orthopyroxene + metal (Irving et al., 2013) and through its sulfurization by a S-rich fluid or gas to form orthopyroxene + sulfide (e.g., Singerling et al., 2013).

A noble gas study was conducted by Murty et al. (2007), and it was found that NWA 1500 retains very low abundances of trapped noble gases compared to ureilites. Moreover, the Ar and Xe isotopic ratios were found to differ significantly from ureilites, the cause of which cannot be attributed to terrestrial weathering. A noble gas isotopic plot gives values for NWA 1500 that fall within the brachinite field. In addition, they concluded that the N systematics were unlike that of ureilites. Utilizing the plagioclase grains to determine the 26Al closure age of NWA 1500, it was found to have formed at least 7 m.y. after CAIs; this establishes a younger age for NWA 1500 than for Brachina. Brachina is distinguished in significant ways from the other brachinites (e.g., nearly chondritic composition, high plagioclase abundance [~10 vol%]), and it is the most primitive brachinite known (Greenwood et al., 2017 and references therein).

Murty et al. (2007) also calculated a CRE age for NWA 1500 of 9.4 m.y. A similar 21Ne-based CRE age was obtained for NWA 1500 by Beard et al. (2018) in a subsequent noble gas study. From their analyses of 15 brachinite and brachinite-like meteorites, together with the literature values for seven others, Beard et al. (2018) identified three potential CRE age clusters. The youngest cluster reflects a possible ejection event that occurred ~10.5 (±1.1) m.y. ago, comprising the two brachinite-like meteorites NWA 1500 and NWA 4518, and the two brachinites ALH 84025 and Reid 013. Importantly, two of these CRE age clusters include both brachinite and brachinite-like meteorites, which attests to a common parent body for all of these meteorites (see diagram below). standby for o-cr diagram
click on image for a magnified view

Diagram credit: Beard et al., 81st MetSoc, #6170 (2018) Results of an in-depth study of this anomalous meteorite were presented by C. Goodrich et al. (2005, 2006). They found that many of the petrologic features of NWA 1500 were in fact consistent with accumulation on the ureilite parent body from a high degree fractional melt, which occurred at a greater depth than that at which the most ferroan olivine–pigeonite ureilites formed. The Fe–Mn–Mg composition of olivine in NWA 1500 is consistent with the ratios measured for other augite-bearing ureilites, but it would be a ureilite that contains a larger melt component and has undergone a higher degree of smelting/reduction.

In a subsequent study, Goodrich et al. (2006) provided many examples of textural, chemical, and mineralogical characteristics of NWA 1500 which are consistent with the augite-bearing ureilite group, and they proposed that this is a member of the small group of augite-bearing (lacking pigeonite), monomict ureilites. To account for the many anomalous characteristics shown by NWA 1500, they argued that it experienced higher oxidation given its greater depth of formation, and that it subsequently experienced only slight reduction during ascent as shown by the reverse zoning of olivine; examination of other brachinites for reverse zoning in olivine grains will be beneficial. Low Cr and P in olivine and metal, and the presence of chromite and apatite phases, are also indicative of higher oxidation conditions for this ureilite during formation at greater depth. The presence of plagioclase as poikilitic and intergranular grains is indicative of crystallization from a melt at great depth, and this feature further distinguishes this possible ureilite from all others. Northwest Africa 1500 was equilibrated at lower temperatures than any other ureilite measured, which is consistent with the generally accepted ureilite model involving a breakup with subsequent rapid cooling of its parent body during its magmatic stage.

Further studies of NWA 1500 by Goodrich et al. (2011) determined that texture, modal abundances, mineral compositions, REE abundances, O-isotopic compositions, and siderophile element abundances all follow brachinite trends, and are distinguishable from other olivine-rich, primitive achondrite groups. However, through studies of highly siderophile element (HSE) abundances, and upon examining the metal-sulfide segregation processes, it was determined by Day et al. (2012) that NWA 1500 and similar brachinite-like primitive achondrites were not likely genetically related (i.e. from the same parent body) to brachinites, but rather, originated on similar volatile-rich, oxidized, chondritic precursor asteroids while experiencing similar petrologic processes during their history. Goodrich et al. (2017) determined that brachinites and brachinite-like achondrites have a distinct redox trend and a higher Fe/Mg ratio compared to all other primitive achondrites, consistent with formation in a similar nebula reservoir; therefore, they suggest that brachinites and brachinite-like achondrites be called the brachinite clan.

Notably, an achondrite clast from the Kaidun meteorite has been favorably compared to a brachinite (Higashi et al., 2017, #1874). Verification of this discovery would infer a very old formation age for the Kaidun parent body, since the age of Brachina is 4.564.8 (±0.0005) b.y. The specimen of NWA 1500 shown above is a 3.97 g partial slice.


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NWA 595

Primitive Achondrite, ungrouped
(Brachinite-like; Brachinite in MetBull 86)
standby for northwest africa 595 photo
Purchased November 9, 2000
no coordinates recorded A small, highly weathered (W3/4), but complete stone, weighing 196 g was purchased in M’hamid, Morocco and given the name Northwest Africa 595. Northwest Africa 595 is an olivine-rich primitive achondrite with subchondritic chemistry and mineralogy, and despite some anomalous features like more magnesian silicates, has been grouped by some investigators with the brachinites. Its matrix constituents include minor troilite and chromite.

The brachinite group consists of chemically and mineralogically diverse members. A study of NWA 595 by Irving et al. (2005) revealed an anomalous mineral composition and an O-isotopic composition that plots away from the brachinite group. However, in a followup O-isotopic analysis and petrographic study incorporating a more thorough acid-washing procedure, Irving and Rumble III (2006) did show that NWA 595 is both isotopically and petrologically similar to the brachinite NWA 3151, as well as to the primitive achondrite NWA 4042. The Fe-Mn-Mg relations of NWA 595 olivine show correlations to other brachinites, and as found in many brachinites, fine-grained assemblages of orthopyroxene and opaques lining olivine grain boundaries are present throughout (Goodrich, 2010). At the same time, these three Saharan meteorites have more positive O-isotopic values than Brachina. In their concluding statement (Irving and Rumble III, 69th MetSoc, #5288 [2006]) they suggest that ‘if all these specimens (including Brachina) derive from the same parent body, then it must be isotopically quite heterogeneous.’

This study and a study by Greenwood et al. (2007) both revealed a disparity in O-isotopes between Brachina and some Saharan brachinites, which is consistent with an origin for these Saharan brachinites on a parent body separate from that of Brachina. Other evidence supports such a multiple parent body scenario: some brachinite members exhibit characteristics of primitive achondrites, i.e., have near-chondritic compositions, while others appear to have experienced igneous fractionation with element depletions and contain melt inclusions in olivine. Evidence is also ambiguous among brachinites as to whether they represent cumulates or metamorphic processes. It could be inferred that this varied group represents a diversity of petrogenetic models representing more than a single parent body. However, it is also plausible that the isotopically and petrologically diverse suite of brachinites originated on a very heterogeneous common parent body. If the latter viewpoint is true, then the range of the brachinite group might be too narrowly defined, and perhaps some of the brachinite-like primitive achondrites are also genetically related. Goodrich et al. (2017) determined that brachinites and brachinite-like achondrites have a distinct redox trend and a higher Fe/Mg ratio compared to all other primitive achondrites, consistent with formation in a similar nebula reservoir; therefore, they suggest that brachinites and brachinite-like achondrites be called the brachinite clan.

According to published studies, several factors indicate that NWA 595 and similar brachinite-like achondrites may not be members of the brachinite group. Despite its similarities to the brachinites in chemical composition and Xe-isotopic ratios, the O-isotopic ratios of NWA 595 plot outside of the brachinite field towards the TFL. In addition, FeO/MnO ratios of both olivine and clinopyroxene are lower than for typical brachinites and plot outside of the brachinite field. Moreover, NWA 595 contains more magnesian olivine, lacks plagioclase (along with ALH 84025 and Eagles Nest), and contains an orthopyroxene abundance (10–15 vol%) significantly higher than in typical brachinites; notably, this is 10× the next highest abundance, measured for Hughes 026. The brachinite-like MIL 090206 has similar abundances of opx and magnesian olivine to NWA 595 (Goodrich et al., 2012). Moreover, through studies of highly siderophile element (HSE) abundances, and upon examining the metal-sulfide segregation processes, it was determined by Day et al. (2012) that NWA 595 and similar brachinite-like achondrites were not likely genetically related (i.e. from the same parent body) to brachinites, but rather, originated on similar volatile-rich, oxidized, chondritic precursor asteroids while experiencing similar petrologic processes during their formation history.

Many of the known brachinites have disparate cosmic-ray exposure ages, indicating that they represent numerous separate ejection events. According to a study by Patzer et al. (2003), the CRE ages of EET 99402/407, Hughes 026, and Eagles Nest form a cluster at ~48 m.y., and those of Reid 013 and ALH 84025 coincide at ~10 m.y. In a separate study by Ma et al. (2003), the cosmogenic nuclide calculations establish a range of CRE ages from 4 m.y. for Brachina to ~25.5 m.y. for Eagles Nest. From their noble gas analyses of 15 brachinite and brachinite-like meteorites, together with the literature values for seven others, Beard et al. (2018) identified three potential CRE age clusters. The intermediate cluster reflects a possible ejection event that occurred ~25.0 (±3.4) m.y. ago, comprising the five brachinites LEW 88763, NWA 3151, NWA 4874, NWA 7297, and RaS 309, and the three brachinite-like meteorites NWA 595, NWA 6077, and NWA 8777. It should be noted that although the FeO-rich LEW 88763 is currently classified as a brachinite, new analyses by Day et al. (2015) led them to propose a reclassification as anomalous achondrite, with a possible relationship to the ungrouped achondrite NWA 6704 pairing group. Importantly, two of the resolved CRE age clusters include both brachinite and brachinite-like meteorites, which attests to a common parent body for all of these meteorites (see diagram below). standby for o-cr diagram
click on image for a magnified view

Diagram credit: Beard et al., 81st MetSoc, #6170 (2018) A transmitted light view of a petrographic thin section of NWA 595 can be seen on John Kashuba’s page. The specimen of NWA 595 shown above is a 0.81 g partial slice.


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DIVNOE

Achondrite, ungrouped
(brachinite-like)
standby for divnoe photo
Found September 1981
45° 42′ N., 43° 42′ E. After cutting a field of grass located 36 km southeast of the settlement of Divnoe, in the Stavropol region of Russia, a single mass of 12.7 kg was found. The meteorite had a rusty brown fusion crust indicating a significant terrestrial residence time. Divnoe is an olivine-rich (~70 vol%) achondrite with subchondritic chemistry and mineralogy. It contains an opaque-rich, fine-grained lithology (ORL) along with patches of pyroxene and plagioclase (PP), within a coarse-grained olivine groundmass (CGL). Veins of troilite and rare metal occur throughout.

Formation of this meteorite began as a chondritic body (trapped xenon isotopic patterns are the same as those of ordinary chondrites) that experienced 20 wt% partial melting at 1300°C (Petaev et al., 1994). The measured HSE abundances in Divnoe are consistent with a partially melted parent body in which heating from short-lived radionuclides came to a halt before a core was fully formed. Terrestrial contamination makes an accurate K–Ar gas retention age difficult to determine. After crystallization of 60 wt% of the partial melt, the remaining 40 wt% Na and K-rich liquid portion of the melt was segregated. The CGL and metal components are consistent with the residue after extraction of the melt, while the PP component represents a partial melt phase that was trapped and crystallized within the rock. The ORL component was formed late in the partial melt phase by reaction between sulfur vapor and residual olivine. All of this material experienced extensive recrystallization during slow cooling from 1000°C to 500°C, after which a secondary reheating event increased the temperature to 700°C, perhaps as a result of impact ejection from the parent body 17.2 m.y. ago. This was followed by low-temperature annealing, which erased most of the shock features and produced the unique olivine lamellar structure.

An alternative explanation for the observed crystallographic preferred orientation (CPO) of Divnoe olivine grains was proposed by Hasegawa et al. (2014, 2015), who argued that this fabric texture was the result of crystal accumulation at the bottom of a convecting magma chamber. However, in recognition of the mutually consistent description of Divnoe as a residue of partial melting, they concluded that the rock must have experienced a complex petrogenetic history probably involving melt flow. Notably, the brachinite-like achondrite NWA 6112 and brachinite EET 99407 have a similar O-isotopic compositions and CPO patterns as Divnoe.

Divnoe is similar to the brachinite group in chemical composition and in oxygen and xenon isotopic ratios. Similarities also exist in O-isotopic and bulk chemical composition between Divnoe and the HED suite (particularly diogenites), although some major differences exclude a common origin. On the other hand, the bulk chemical composition of Divnoe and a related anomalous achondrite, RBT 04239, matches that of the brachinites Brachina and ALH 84025 very closely, consistent with a derivation from a common precursor (Weigel et al.,1996). Moreover, primordial trapped noble gases indicate that both similarities and differences exist between Divnoe and the brachinites, while at the same time revealing a ~100 m.y. difference in their crystallization ages. The paired ungrouped Antarctic meteorites RBT 04255 and RBT 04239 also show some similarities to Divnoe.

On a newly compiled O-isotope diagram for brachinites and other planetary achondrites, published by Rumble III et al. (2008), Divnoe has a Δ17O value that plots with Brachina, and these investigators believe that Divnoe should probably be lumped with the brachinites. However, through their studies of highly siderophile element (HSE) abundances, and upon examinination of the metal-sulfide segregation processes, Day et al. (2012) determined that Divnoe and similar brachinite-like achondrites were not likely genetically related (i.e. from the same parent body) to brachinites, but instead, they argued that these meteorites originated on similar volatile-rich, oxidized, chondritic precursor asteroids that experienced similar petrologic processes during their formation history. Goodrich et al. (2017) determined that brachinites and brachinite-like achondrites have a distinct redox trend and a higher Fe/Mg ratio compared to all other primitive achondrites, consistent with formation in a similar nebula reservoir, and they suggest that brachinites and brachinite-like achondrites be called the brachinite clan.

Evidence for differences in redox conditions between brachintes and brachinite-like achondrites during formation is demonstrated by Crossley et al. (2018) on a coupled Δ17O vs. Fe/Mg diagram. It is apparent that Divnoe and other brachinite-like achondrites contain olivine that is less ferroan than that in brachinites, which supports the contention that they derive from distinct parent bodies (see diagram below). standby for o vs. fe/mg diagram
Diagram credit: Crossley et al., 49th LPSC, #2540 (2018) Recent advanced spectrographic techniques were applied to a set of 1,478 meteorite spectra and to members of the Eos family of asteroids, traditionally considered to be a good match to the CO/CV chondrites (Mothé-Diniz and Carvano, 2005). It was concluded that Divnoe was actually a much better, and very close spectral match to these asteroids, especially as compared to asteroids 221 Eos and 653 Berenike (see diagram below). Although the CRE age, or transport time, of the Divnoe meteorite to Earth of 17.2 m.y. is considerably less than that predicted for transport from the 9:4 resonance near the Eos family region (50 m.y. minimum; di Martino et al., 1997), a collisional cascade process could explain the discrepency. In support of this theory, the calculated inefficiency of the delivery process from the Eos region to Earth (~2%) might be considered commensurate with the rarity of the brachinites and brachinite-like meteorites in our collections. Furthermore, the breakup of the partially differentiated parent body of Divnoe would be expected to produce a highly diverse group of fragment lithologies, and this is exactly what is observed throughout the Eos family. The specimen of Divnoe shown above is a 0.19 g thin cut fragment. standby for 9:4 resonance diagram
Diagram credit: M. M. M. Meier et al., Earth and Planetary Science Letters, vol. 490 (2018)
‘Cosmic history and a candidate parent asteroid for the quasicrystal-bearing meteorite Khatyrka’
(https://doi.org/10.1016/j.epsl.2018.03.025)