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 Click on Term to Read More, 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). Click on Term to Read More
(Ureilite [olivine-augite type] in MetBull 87)
no coordinates recorded
A single, partially fusion-crusted stone weighing 3.3 kg was purchased in Zagora, Morocco. 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 Click on Term to Read More
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 reductionOxidation 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 Click on Term to Read More
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 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 Click on Term to Read More
grains (~95 vol%) along with melt pockets and secondary veins containing a heterogeneous distibution of Ca-rich 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 Click on Term to Read More
(2–3 vol%), chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups. Click on Term to Read More
(0.6–1.6 vol%), 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 Click on Term to Read More
(0.7–1.8 vol%), andesine, and diopside. Other constituents include FeNi-metal, 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 Click on Term to Read More
(not found subsequently), lonsdaleiteHexagonal polymorph of carbon (C) that forms from meteoric graphite during impact. The immense heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice (below). Lonsdaleite was first identified from the Canyon Diablo meteorite at Barringer Crater (also known as Meteor Crater) in Click on Term to Read More
, and diamondOne of the naturally occurring forms of carbon found in meteorites. Each C atom is bonded through covalent sp3 hydrid orbitals to four others. The strength of the C-C bonds makes diamond the hardest naturally occurring substance (according to the Mohs scale) in terms of resistance to scratching. There are Click on Term to Read More
. The high olivine fayalitePure* iron end-member (Fe2SiO4) of the olivine solid solution series and an important mineral in meteorites. When iron (Fe) is completely substituted by magnesium, it yields the the pure Mg-olivine end-member, forsterite (Mg2SiO4). The various Fe and Mg substitutions between these two end-members are described based on their forsteritic (Fo) Click on Term to Read More
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.
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 equilibriumTerm used to describe physical or chemical stasis. Physical equilibrium may be divided into two types: static and dynamic. Static equilibrium occurs when the components of forces and torques acting in one direction are balanced by components of forces and torques acting in the opposite direction. A system in static Click on Term to Read More
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 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. Click on Term to Read More
. 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 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. Click on Term to Read More
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 winonaitea partially differentiated asteroid that was disrupted just as it began to form an Fe core and a silicate-rich crust. This disrupting impact mixed silicates into molten Ni-Fe metal forming the silicated IAB irons, and mixed olivine-rich residues of partial melts into unmelted silicates, forming the winonaites. A few winonaites Click on Term to Read More
/IAB field near the lodraniteRare type of primitive achondrite named after the Lodran meteorite that fell in Pakistan in 1868. Initially, lodranites were grouped with the stony-iron meteorites because they contain silicates (olivine, orthopyroxene, and minor plagioclase) and Fe-Ni metal in nearly equal proportions. However, since discovery of the closely related acapulcoite group, lodranites Click on Term to Read More
/acapulcoite field, and was very close to the brachinite-like, primitive achondriteAchondrite with an almost chondritic composition with age similar to the primordial chondrites. These should be better classified as "metachondrites".
Divnoe. It did not fit the results expected for the isotopic fractionationConcentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process. Click on Term to Read More
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 (Δ17
O = –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 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 Click on Term to Read More
containing abundant Ni-free 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 Click on Term to Read More
grains, causing 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
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, ultramaficTerm used for silicate minerals with cations predominantly Mg and/or Fe. Mafic minerals are dominated by plagioclase and pyroxene, and also contain smaller amounts of olivine. Click on Term to Read More
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 acapulcoitesPrimitive achondrite that belongs to a small group named after the Acapulco meteorite that was observed to fall in Mexico in 1976. Acapulcoites are made mostly of fine-grained olivine (Fo3-14), orthopyroxene(En86-97), Ca-rich pyroxene (En51Wo44), plagioclase (An12-31), Ni-Fe metal, and troilite. They are transitional between primordial chondritic matter and more differentiated Click on Term to Read More
should be compared.
Goodrich et al.
(2006, 2010) observed fine-grained assemblages of orthopyroxeneOrthorhombic, low-Ca pyroxene common in chondrites. Its compositional range runs from all Mg-rich enstatite, MgSiO3 to Fe-rich ferrosilite, FeSiO3. These end-members form an almost complete solid solution where Mg2+ substitutes for Fe2+ up to about 90 mol. % and Ca substitutes no more than ~5 mol. % (higher Ca2+ contents occur Click on Term to Read More
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.
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. Click on Term to Read More
study was conducted by Murty et al.
(2007), and it was found that NWA 1500 retains very low abundances of 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. Click on Term to Read More
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 fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If Click on Term to Read More
within the brachinite field. In addition, they concluded that the N systematics were unlike that of ureilites. Utilizing the plagioclase grains to determine the 26
Al closure age of NWA 1500, it was found to have formed at least 7 m.y. after 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 Click on Term to Read More
; 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 21
Ne-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). 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–pigeoniteLow-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, found as a major mineral in eucrites and shergottites. In order to be considered pigeonite, the clinopyroxene must contain 5 to 20 mol % of calcium (Wo5 - 20). Chondrites of petrologic types 4 and below contain significant low-Ca clinopyroxene. During metamorphism to higher temperatures, all existing
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 oxidationOxidation 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 Click on Term to Read More
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 crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. Click on Term to Read More
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, 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 Click on Term to Read More
compositions, REEOften abbreviated as “REE”, these 16 elements include (preceded by their atomic numbers): 21 scandium (Sc), 39 Yttrium (Y) and the 14 elements that comprise the lanthanides excluding 61 Promethium, an extremely rare and radioactive element. These elements show closely related geochemical behaviors associated with their filled 4f atomic orbital. Click on Term to Read More
abundances, O-isotopic compositions, and 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
abundances all follow brachinite trends, and are distinguishable from other olivine-rich, primitive achondrite groups. However, through studies of highly siderophile elementSubstance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of Click on Term to Read More
(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, 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 Click on Term to Read More
, 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 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 Click on Term to Read More
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 Click on Term to Read More
reservoir; therefore, they suggest that brachinites and brachinite-like achondrites be called the brachinite clan.
Notably, an achondrite clastA mineral or rock fragment embedded in another rock. Click on Term to Read More
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.