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 26Al (aluminum isotope) and gravitational, 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). (brachinite-like)
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 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 had a rusty brown fusion crustMelted 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. 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 pyroxeneA 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. and plagioclaseAlso 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 (PP), within a coarse-grained 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 groundmass (CGL). Veins of troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites. and rare 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 occur throughout.
Formation of this meteorite began as a chondritic body (trapped xenon isotopic patterns are the same as those of ordinary 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) that experienced 20 wt% partial meltingAn 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 at 1300°C (Petaev et al., 1994). The measured HSE abundances in Divnoe are consistent with a partially melted 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. in which heating from short-lived radionuclides came to a halt before a coreIn 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. was fully formed. Terrestrial contamination makes an accurate K–Ar gas retention age difficult to determine. After crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. 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 magmaMolten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. 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 oxygenElement 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 and xenon isotopic ratios. Similarities also exist in O-isotopic and bulk chemical composition between Divnoe and the HED suite (particularly diogenitesDiogenites belong to the evolved achondrite HED group that also includes howardites and eucrites. They are named after the Greek philosopher Diogenes of Apollonia, of the 5th century BCE, who was the first to suggest that meteorites come from outer space (a realization forgotten for over 2,000 years). They are), 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 gasesElement 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. 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 elementLiterally, "iron-loving" element that tends to be concentrated in Fe-Ni metal rather than in silicate; these are Fe, Co, Ni, Mo, Re, Au, and PGE. These elements are relatively common in undifferentiated meteorites, and, in differentiated asteroids and planets, are found in the metal-rich cores and, consequently, extremely rare on (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, oxidizedOxidation 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, 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 redoxOxidation 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 trend and a higher Fe/Mg ratio compared to all other primitive achondrites, consistent with formation in a similar nebulaAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive 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). 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. 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)