EL3/6, impact-melt brecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Click on Term to Read More
‘Fossil’ or ‘Paleo’ 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
(EL6/7 in MetBull 91; aubriteAubrites are named for the Aubres meteorite that fell in 1836 near Nyons, France. They are an evolved achondrite that is Ca-poor and composed mainly of enstatite (En100) and diopside (En50Wo50) with minor amounts of olivine (Fa0) and traces of plagioclase (An2-8). They contain large white crystals of enstatite as Click on Term to Read More pairing in MetBull 92)
Revised classifications have been submitted to NomCom and MetBull
click on photo for an enlarged view Purchased August 2005
27° 30′ N., 12° 30′ W. Numerous individual pieces of an extensively weathered ‘relict’* or fossil meteoriteThe textural, mineralogical or compositional remnant within a sedimentary rock of a meteorite that fell millions of years ago and found in Ordovician limestone from Sweden. Read Tiny Traces of a Big Asteroid Breakup for a complete writeup on this subject. In picture to the left a nautiloid shell is Click on Term to Read More, weighing together as much as 3,000 kg, were found in Western Sahara, reportedly near the village of Al Haggounia. Stones of various sizes were found both on top of the surface and buried under the soil in geological strataOriginally horizontal layers of rock. associated with both quaternary limestones and cretaceous limestones. This is evidence that the 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 occurred later than the deposition of these strata (Chennaoui et al., 2007). The 14C age of this meteorite was determined by Chennaoui–Aoudjehane et al. (2009) to be 23 (±2) t.y., in agreement with geological evidence.
A large portion of this meteorite was purchased by a collector at the 2006 Tucson Gem and 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
Show and in subsequent purchases from a Moroccan source. The vast majority of Northwest Africa 2965 is surface material which is very highly weathered and dark brown in color with a porosityThe volume percentage of a rock that consists of void space. Vesicular porosity is a type of porosity resulting from the presence of vesicles, or gas bubbles, in igneous rock such as the pumice presented here. Vesicular porosity is very rare in meteorites and is often associated with slag, one Click on Term to Read More
of 40%. It contains an abundance of very dark fractures filled with 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
products such as goethite. Although primary minerals are present (e.g.
, 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). Click on Term to Read More
, 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
, troiliteBrass colored non-magnetic Fe sulfide, FeS, found in a variety of meteorites.
, daubreelite, alabanditeMagnesium sulfide found in aubrites and EL chondrites. Its formula is MnS. Click on Term to Read More
, oldhamiteMn-Ca sulfide, (Mn,Ca)S, is a pale to dark brown accessory mineral found in minor amounts in highly reduced meteorites such as many enstatite chondrites, and some aubrites and enstatite achondrites. Oldhamite in enstatite chondrites likely formed by solar nebular gas condensation. CaS Oldhamite was also found in the most fresh Click on Term to Read More
, and others), secondary mineralsMineral that forms through processes such as weathering, and in the case of meteorites can also include pre-terrestrial alteration. Secondary minerals in meteorites that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic Fe-Ni by oxidation, phosphates formed by the alteration of schreibersite, and sulfates formed by Click on Term to Read More
occur throughout, including those within the mm- to cm-size ubiquitous pores, considered by some to have formed by weathering of 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
phases. However, in his study of the Al Haggounia 001 pairing, A. Rubin (2016) attributed the presence of these vesicles (~6.8 vol%) to impact-induced evaporationProcess in which atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. Click on Term to Read More
of sulfides, in a similar manner to those in the aubrite Mayo Belwa. He reasoned that the sparsity of metal observed in some parts of the mass, especially in the less weathered bluish-gray portions, is the result of metal–sulfide melt drainage into nearby regions as represented by Al Haggounia 001 with its large component of limonite (32.6 vol%) replacing FeNi-metal (0.29 vol%) along with sulfide (4.0 vol%).
A very low abundance of radial 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 chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
have been identified (<5 vol%), as well as other fine-grained, rounded enstatite and plagioclase aggregates. The chondrules contain a Na–Al–Si–rich glass phase consistent with an unequilibrated chondriteA chondrite with heterogeneous mineral compositions (e.g., olivine grains with differing FeO/(FeO+MgO) ratios.
. Recognizing this scarce population of chondrules and the other unequilibrated features of this meteorite has finally enabled investigators to arrive at a consensus for the classification of this possibly ‘fossil’ meteorite.
Northwest Africa 2965 was initially analyzed at Northern Arizona University (T. Bunch and J. Wittke), and due to its apparent lack of chondrules and its fine-grained igneous-like matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More
, it was determined to be a recrystallized EL6/7 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 Click on Term to Read More
. An alternate classification of this enstatite meteorite as the first enstatite metachondriteTerm used to describe a metamorphosed chondrite. Also referred to as a type 7 chondrite. Metachondrites are texturally evolved rocks derived from chondritic precursors and some have been classified as primitive achondrites. Click on Term to Read More
, a newly proposed metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. Click on Term to Read More
category defined by Irving et al.
(2005), was also considered. Subsequent to this study, additional material reported to be from the same meteorite, but having a less altered bluish color, was studied at the University of Washington, Seattle (A. Irving and S. Kuehner). This material was classified as an EL3 chondrite (the likely paired NWA 2828 was classified as an aubrite in MetBull 91).
This meteorite contains only trace amounts of FeNi-metal, but some portions near the top strata bear a dark goethite-rich rind consistent with leaching of Fe from the interior of the stone during an extended terrestrial residence in a wetland location. Analyses of the trace FeNi-metal and of rare 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 Click on Term to Read More
inclusions identified within enstatite grains of NWA 2828 revealed a Si content consistent with EL 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 Click on Term to Read More
, but different from aubritesAubrites are named for the Aubres meteorite that fell in 1836 near Nyons, France. They are an evolved achondrite that is Ca-poor and composed mainly of enstatite (En100) and diopside (En50Wo50) with minor amounts of olivine (Fa0) and traces of plagioclase (An2-8). They contain large white crystals of enstatite as Click on Term to Read More
(Irving et al.
, 2010). The investigation also determined that while major elements are depleted, trace siderophile elements still have abundances typical of E chondrites and were possibly preserved through an electroplating process. According to investigator T. Bunch (pers. comm.), this meteorite contains very tiny prismatic enstatite crystals with µm-sized oblate-to-spherical glass inclusions that might be presolar condensates. Also present are vermicular 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*. Click on Term to Read More
, well-formed and poorly-formed ‘graphite’, and unresolved carbon grains (<2 µm in size).
Prior to the analyses of NWA 2965, a 171.5 g stone with an identical appearance was analyzed at the Lunar & Planetary Laboratory, University of Arizona (Lowe, Hill, Domanik, and Lauretta), and the Southwest Meteorite Laboratory, Payson, Arizona (Killgore). The details of their analysis and the reasons for their ultimate classification can be found in the abstract NWA 2736: An unusual new graphite-bearing aubrite
. They conclude that NWA 2736
has an igneous texture, and is best described as an unusual enstatite achondriteUsed in past as synonym for Aubrites. Present definition from the Meteoritical Bulletin states that this rare class is an "enstatite-rich achondrite that has not yet been classified into a group". Click on Term to Read More
(aubrite) rather than an enstatite metachondrite or enstatite impact melt. Notably, they compare the impact-shock features to those of Happy Canyon, which is typically classified as a highly metamorphosed EL chondrite rather than an aubrite.
Utilizing a larger volume of this meteorite that provided a better representation of its various components, investigators from NAU and UWS have released results of their most exhaustive study to date at the Fall 2006 Meeting of the American Geophysical Union. They suggest that all of the similarities found among NWA 2965, NWA 2736, and NWA 2828 make it likely that these independently classified stones, along with NWA 4232 and several others, are paired. In further support of a pairing, they determined that all of these stones share a common subsurface excavation site in Algeria delimiting a 40 km strewn fieldArea on the surface containing meteorites and fragments from a single fall. Also applied to the area covered by tektites, which are produced by large meteorite impacts. Strewnfields are often oval-shaped with the largest specimens found at one end. Given that the largest specimens go the greatest distance, a meteoroid's
. Based on visual evidence, the previously classified EL6 chondrite NWA 002
, a meteorite purchased in Morocco in 1999 having an appearance virtually identical to NWA 2965, may also belong to this pairing group.
Succeeding excavation at the strewn field led to the recovery of several large masses which were studied at Université Pierre & Marie Curie, Paris (A. Jambon, O. Boudouma, and D. Badia) under the name Al Haggounia 001. A classification of aubrite was assigned to this material in light of its enstatite and plagioclase composition (MetBull 92), but the documented existence of terrestrially weathered chondrules in this meteorite should disqualify this classification (see The Al Haggounia ‘Fossil or Paleo’ Meteorite Problem
Subsequent studies of Al Haggounia by Devaux et al.
(2011) found that the ordering of carbon in the matrix indicates that it has experienced significant metamorphism. This crystalline carbon as well as the overall textures of this material prompted them to classify this meteorite as a type 6. Contrariwise, the lack of recrystallization/equilibration in this meteorite has been cited by some investigators as evidence against a petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes.
as high as 6. It was proposed by T. Bunch (pers. comm.) that this meteorite could represent an unequilibrated primitive regolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles). Click on Term to Read More
that formed without chaotic, turbulent mixing on an E-type asteroid. However, in his study of the Al Haggounia 001 pairing, A. Rubin (2016) noted multiple features which indicate this meteorite is an impact-melt breccia, including the following: vesicles produced by troilite evaporation and preserved through quenching, euhedral lath-like 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
grains, kamacite-rich veins; melt globules; partially resorbed chondrules; enstatite nucleation on relict 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
grains and relict chondrules; shock-induced silicate darkening; shock deformation and mosaicism of silicates; quenched feldspathic glass containing trapped, rounded enstatite inclusions; depletion of siderophile elements; and depletion in elements associated with various sulfides.
<!– with millimeter-sized, rounded inclusions consisting of coarse-grained 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
, sparsely distributed in this meteorite (see photo below). These inclusions are highly recrystallized and equilibrated features, and while they offer no petrographic evidence as to their nature, they are likely remnants of pre-existing chondrules. Northwest Africa 2965 has undergone heavy oxidation since its arrival on Earth, as attested by the many calcite veins intruding the stone; it has a weathering grade of W2–W5.
–> Images of distinct chondrules present in this meteorite can be seen on J. Kashuba’s NWA 2965 page
. In their study of multiple samples of this meteorite, Leili et al.
) identified a wide range of chondruleRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
types including rimmed macrochondrules/clasts up to 11 × 6 mm in size. The specimen of NWA 2965 shown above is a 30 g slice exemplifying the disparate weathering grades in contact with each other (e.g.
, a small portion of the less weathered, bluish-colored clastA mineral or rock fragment embedded in another rock. Click on Term to Read More
is attached on the right side. The top photo below is a close-up of a 7.4 g slice of NWA 2965 exhibiting a dense web of oxide-filled fractures and an oval enstatite or plagioclase aggregate. The bottom photo shows a 4.1 g partial end section exhibiting a distinct bluish coloration representing the less altered material of this extensive findMeteorite not seen to fall, but recovered at some later date. For example, many finds from Antarctica fell 10,000 to 700,000 years ago. Click on Term to Read More
. *Relict meteorites, defined as those highly altered meteorites which are >95% replaced by secondary phases since their fall, comprise a new category adopted by the Committee on Meteorite Nomenclature in October 2006.