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)
Fell April 9, 1919 36° 50′ N., 84° 21′ W. Several stones fell in Whitley County, Kentucky at noon after the appearance of a fireballA fireball is another term for a very bright meteor, generally brighter than magnitude -4, which is about the same magnitude of the planet Venus as seen in the morning or evening sky. A bolide is a special type of fireball which explodes in a bright terminal flash at its end, often with visible fragmentation. and sonic booms. The largest fragment recovered was estimated to weigh 31 pounds. As with most 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, Cumberland Falls is a polymict brecciaGeneral term for all breccias that are neither monomict nor dimict. Modified from image source: http://www.saharamet.com/meteorite/gallery/HED/index.html. composed of chalky-white 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). fragments, along with accessory 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, iron sulfide, and 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. 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 patterns in Cumberland Falls metal provide evidence of a 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. process. This process has been characterized as occurring either through quenching of an impact-produced metallic melt, or through crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. within a magmaMolten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. chamber (van Acken et al., 2010).
Unlike typical aubrites, Cumberland Falls contains xenolithic inclusions of a unique type of forsteritic chondrule-bearing material having a bulk composition, mineralogy, O-isotopic affinity, 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 size, and chondrule textural type similar to those of LL 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. However, the HSE depletion in these inclusions is not observed in LL chondrites (van Acken et al., 2012). The aubrite ALHA78113 (Verkouteren and Lipschutz, 1983), the 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).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 Acfer 370 (Moggi-Cecchiare et al., 2009), the ungrouped chondrite NWA 7135 (Irving et al., 2015), and the ungrouped chondrite El Médano 301 (see photo; Pourkhorsandi et al., 2016, 2017) are the only other meteorites that are characterized by this unique forsteritic (Fa0.7 in Cumberland Falls) 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 composition. In addition to these, Peña Blanca Spring reflects a chondritic 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. signature during stepped heating (Miura et al., 2006), suggesting that microscopic chondritic inclusions are present. The nature of the association of the enstatite with the chondritic inclusions in Cumberland Falls suggests that the chondritic object was disrupted by collision with the enstatite 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., during which it experienced severe shock, heat-generated 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, and rapid cooling. This energetic event is attested by miniscule blebs of metallic FeNi and sulfide dispersed in the silicate grains producing silicate darkening, undulose to mosaic extinctionIn astronomy, the dimming of starlight as it passes through the interstellar medium. Dust scatters some of the light, causing the total intensity of the light to diminish. It is important to take this effect into account when measuring the apparent brightness of stars. The dark bands running across portions with planar fractures in 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, impact-melt clasts, and a shock stageA petrographic assessment, using features observed in minerals grains, of the degree to which a meteorite has undergone shock metamorphism. The highest stage observed in 25% of the indicator grains is used to determine the stage. Also called "shock level". of S2–S3 (A. Rubin, 2010). The forsteritePure* magnesium end-member (Mg2SiO4) of the olivine solid solution series and an important mineral in meteorites. When magnesium (Mg) is completely substituted by iron, it yields the the pure Fe-olivine end member, fayalite (Fe2SiO4). The various Fe and Mg substitutions between these two end-members are described based on their forsteritic (Fo) fragments were incorporated in the 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). of the aubrite host, and annealed under pressure to form the polymict 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 that we see today. Shock-derived jadeitic 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. has not been found in any other 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.
Through studies of the chondritic inclusions in Cumberland Falls, the 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. was ascertained by Binns (1969) to be mostly type 3 and 4, and by Kuehner et al. (2016) to be type 6. By comparison, the F chondritesForsterite Chondrites or F-Chondrites are presently only known as inclusions in other meteorites and described by certain lithologies of the Cumberland Falls aubrite. They are thought to have derived from a small and primitive asteroid of F chondritic composition that collided with the aubrite parent body shortly after their formation Acfer 370, NWA 7135 are petrologic type 3/4, and El Médano 301 is petrologic type 4. Results of O-isotope analyses for the Cumberland Falls inclusions, NWA 7135, and El Médano 301 show that the values overlap and establish a unique trend line between the ordinary chondrites and the TFL (see 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 onlyisotopeOne of two or more atoms with the same atomic number (Z), but different mass (A). For example, hydrogen has three isotopes: 1H, 2H (deuterium), and 3H (tritium). Different isotopes of a given element have different numbers of neutrons in the nucleus. diagrams below). See the NWA 7135 page for further information regarding these forsterite inclusions in Cumberland Falls and their association with this F chondriteForsterite Chondrites or F-Chondrites are presently only known as inclusions in other meteorites and described by certain lithologies of the Cumberland Falls aubrite. They are thought to have derived from a small and primitive asteroid of F chondritic composition that collided with the aubrite parent body shortly after their formation grouplet. Diagram credit: Kuehner et al., 78th MetSoc, #5238 (2015)
Diagram credit: Kuehner et al., 47th LPSC, #2304 (2016)
Diagram credit: Pourkhorsandi et al., GCA, vol. 218, p. 109 (2017) ‘The ungrouped chondrite El Médano 301 and its comparison with other 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 ordinary chondrites’ (https://doi.org/10.1016/j.gca.2017.09.013) The pre-atmospheric diameter of Cumberland Falls, as calculated from cosmogenic production rates, was 160–200 cm—quite large by aubrite standards. Just as all aubrites exhibit complex irradiation histories, both on the parent body and in space, Cumberland Falls presents a 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 range of 49 (±10) m.y., based on 81Kr–Kr, to 60.9 m.y. This CRE age is consistent with a possible cluster that might include Pesynoe (~40 m.y.), (Bishopville (52 ±3 m.y.), Bustee (52.6 m.y.), Khor Temiki (53.9 m.y.), Y-793592 (55.0 m.y.), and LEW 87007 (58.5 m.y.), while Pena Blanca Spring (75 ±11 m.y.) and LAP 02233 (78 ±12 m.y.) are only slightly higher. However, since pre-irradiation within the regolith of the parent body likely accounts for a component of these exposure ages, doubts are raised concerning the likelihood of their common ejection (Lorenzetti et al., 2003). It has been suggested that a minimum of four, and as many as nine breakup events occurred on the aubrite parent body. In light of their higher than average neutron-capture-produced noble gas components, Cumberland Falls and Bishopville are considered to have resided near the surface of the aubrite parent body.
For additional information on the formation of the aubrite group visit the Mayo Belwa page. The photo above shows a 1.22 g partial slice sectioned through a black chondritic inclusionFragment of foreign (xeno-) material enclosed within the primary matrix of a rock or meteorite.. The top photo below shows a closeup view of a chondritic inclusion in a large mass curated at the National Museum of Natural History, Smithsonian Institution. The bottom photo is an excellent petrographic thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope. micrograph of Cumberland Falls, shown courtesy of Peter Marmet.
On display at Smithsonian National Museum of Natural History Photo courtesy of Martin Horejsi
click on image for a magnified view Photo courtesy of Peter Marmet