NWA 6675

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 (main-group)

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Found 2010
no coordinates recorded A single heavily weathered stone weighing 510 g was found in the Sahara and subsequently sold to G. Tomelleri in Erfoud, Morocco in 2010. Analyses were conducted at the Museo di Scienze Planetarie in Italy (Vanni Moggi Cecchi), and NWA 6675 was classified as an 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"., or aubrite. Northwest Africa 6675 is a rare unbrecciated (common only to the 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 Mt. Egerton and Shallowater), cumulate-textured aubrite, formed through igneous processes and fractional crystallation. It is considered likely that this 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 is part of a large pairing group, additionally comprising the NWA-series numbers 4537, 4799, 4832, 4871, 5217, 5419, 5885, 6193, 6350, and probably the largest and least weathered mass, 7214, all of which together weigh 5,047.6 g.

A large proportion (~40%) of aubrites are witnessed falls, which is thought to reflect the fact that these highly reducedOxidation 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 meteorites are particularly susceptible to terrestrial weathering once they arrive on Earth. The surprisingly rapid alteration processes that affect all aubrites in Earth’s oxidizingOxidation 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 and wet environs is demonstrated visually in the following photos of stones from a common 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. On the left, shown courtesy of Darryl Pitt, is the fresh (W0/1) 2.2 kg NWA 7214 stone that was recovered in 2006, exhibiting a high content of FeNi-metal flakes throughout with virtually no visible 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. The two much smaller stones—the 510 g NWA 6675 in the middle and the 50.5 g NWA 6350 stone on the right—had both remained in the terrestrial environment until their recovery in 2010 and have sustained considerable weathering; the 10× larger NWA 6675 stone has experienced significantly less alteration than NWA 6350 probably due to their comparative sizes.

Keil (2010) suggests that the extremely reducingOxidation 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 conditions under which aubrites formed is evidence for a location within 1 AUThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The of the SunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the, but on a 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. other than any of the known E 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 or the Shallowater source object. The size of the differentiated aubrite planetesimal(s) is constrained by those processes which caused it to melt. Arguments suggesting that the heat source was the decay of short-lived radionuclides such as 26Al have not been reconciled with the apparent low Al 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 contents in aubrites. In a similar manner, John T. Wasson (2016) presented evidence that the slow heating generated entirely by the decay of 26Al is insufficient to melt asteroids, and that an additional heat source would have been required; e.g., the rapid heating incurred from major impact events. He determined that the canonical 26Al/27Al ratio of 0.000052 is much too low to cause any significant melting, and that a minimum ratio of 0.00001 would be required to produce a 20% melt fraction on a well-insulated body having a significant concentration of 26Al. For example, the initial ratio of 0.0000004–0.0000005 calculated for the angrites Sah 99555 and D’Orbigny based on their 26Al–26Mg isochrons is too low to have generated any significant melting without an additional heat source. It has been suggested that relatively small planetesimalsHypothetical solid celestial body that accumulated during the last stages of accretion. These bodies, from ~1-100 km in size, formed in the early solar system by accretion of dust (rock) and ice (if present) in the central plane of the solar nebula. Most planetesimals accreted to planets, but many – such as the aubrite planetesimal(s) might have been just the required size to allow heating by induction in the plasmaFourth state of matter: a gas in which many or most of the atoms are ionized. In the plasma state the atoms have split into positive ions and negative electrons, which can flow freely, so the gas becomes electrically conducting and a current can flow. environment of the T Tauri Sun.

The plot on an oxygen three-isotope diagram calculated for another member of this aubrite pairing group (NWA 4537) lies within the aubrite and 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 field near the TFL (Greenwood and Franchi, OU). Current spectral studies link the aubrites to a few near-Earth Apollo asteroids, specifically 3103 Eger and 434 Hungaria (Kelley and Gaffey, 2002). These two high-albedo, iron-free asteroids are composed of an enstatite-like 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, and are of the appropriate size to make them primary candidates for the aubrite source body. Further evidence has been compiled which is consistent with 3103 Eger being the aubrite source body. For example, the time of day in which aubrites have fallen constrains the orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around to one similar to that of Eger. In addition, the long cosmic-ray exposure ageTime interval that a meteoroid was an independent body in space. In other words, the time between when a meteoroid was broken off its parent body and its arrival on Earth as a meteorite - also known simply as the "exposure age." It can be estimated from the observed effects of aubrites is consistent with a stable residence on a near-Earth asteroidAsteroids with orbits that bring them within 1.3 AU (195 million km) of the Sun. NEAs are a dynamically young population whose orbits evolve on 100-million-year time scales because of collisions and gravitational interactions with the Sun and the terrestrial planets. These asteroids are probably ejected from the main belt that has a long-lived orbit similar to that of Eger. Moreover, the orbital parameters derived for Norton County match those of Eger better than all other orbits. Asteroid 3103 Eger was probably once a member of the Hungaria family of asteroids, located in the innermost asteroid beltBelt located between 2.12 and 3.3 AU from the Sun and located between the orbits of Mars and Jupiter containing the vast majority of asteroids. The asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such at 1.9 AU. It was subsequently ejected into an Earth-crossing orbit. Notably, the asteroid 2867 Steins was recently studied by the Rosetta spacecraft and was found to have an albedoRatio of the amount of light reflected by an object and the amount of incident light. Albedo is used as a measure of the reflectivity or intrinsic brightness of an object. A white, perfectly reflecting surface has an albedo of 1.0 while a black perfectly absorbing surface would have an and spectral properties consistent with those of an aubrite (with an abundance of CaS or 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) (Abell et al., 2008); however, the texture and mineralogy of aubrites indicate they derive from a significantly larger parent body.

For additional information on the formation of the aubrite group visit the Mayo Belwa page. Two photos of a 1.95 g partial slice of NWA 6675 are shown above comparing the effects of different angles of incident light.