Moorabie

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, 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, type 3.5–3.8, low-FeO
(L3.8-an in MetBull 53)

Found before 1965
30° 6′ S., 141° 4′ E. One mass of 31 pounds was found by Mr. L. Russell while prospecting about 130 miles north of Broken Hill close to Boolka, and ~10 miles south of the Moorabie Bore in New South Wales, Australia. 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 representing a large variety of types are closely spaced within a sparse white 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. These chondrules exhibit foliation and preferential alignment, probably produced from an impact-shock event; Moorabie is shocked to stage S4–5. 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 show undulatory 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 Click on Term to Read More and mosaicism. Shock-heating also produced in situ local melting of some FeNi-metal and troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites. Click on Term to Read More grains at temperatures of ~950°C (from a pre-shock accretion-related temperature of ~400°C). These grains coalesced into larger clasts, one of which has been found to enclose chondrules identical to those in the host (Fujita and Kitamura, 1992). In addition, silicate–metal–troilite melt pockets and clear maskelyniteNatural glass composed of isotropic plagioclase produced during shock metamorphism (not melting) at pressures of ~30 GPa. Maskelynite is commonly found in shergottites though also found in some ordinary chondrites, HED and lunar meteorites. It is also found in association with meteorite impact craters and crater ejecta. Named after British Click on Term to Read More are present in the matrix of Moorabie. Slow cooling followed the shock event.

Although Moorabie has been grouped with L-group 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, it forms a group of 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 Click on Term to Read More chondrites (Fa10–13) of mostly H-group association which might represent one or more unique objects distinct from the H, L, and LL ordinary chondriteWork in Progress Ordinary chondrites (OCs) are the largest meteorite clan, comprising approximately 87% of the global collection and 78% of all falls (Meteoritical Society database 2018). Meteorites & the Early Solar System: page 581 section 6.1 OC of type 5 or 6 with an apparent shock stage of S1, Click on Term to Read More parent bodies (Fa16–20). Besides Moorabie, other low-FeO chondrites include Beni Semguine [H5-an], Burnwell [H4-an], Cerro los Calvos [H4-an], Suwahib (Buwah) [H3.8-an], Willaroy [H3.8-an], Wray (a) [H4-an], EET 96031 [H4-like], LAP 04757/73 [H-like], MIL 07273 [H5-an], and QUE 94570 [L-like]. All of these reduced chondrites have 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 outside the established range for the known ordinary chondrite groups. Furthermore, their variable 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 contents, low concentrations of Co in 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, and high troilite contents support a derivation from one or more unique parent bodies.

Notably, the O-isotopic compositions of EET 96031, LAP 04757/73, and MIL 07273 all plot within a region delineated by the H chondrites. The equilibrated chondriteChondrite with minerals of uniform composition (e.g., all of the olivine grains have the same composition) due to diffusion during thermal metamorphism. Such chondrites would be petrologic type 4 (some thermal metamorphism) to type 7 (complete thermal metamorphism of chondritic material). Type 7 chondrites are also referred to as metachondrites. Click on Term to Read More Burnwell is a 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 that has similar low-FeO properties and which initially was shown to plot on an extension of the H–L–LL trend towards more 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 Click on Term to Read More compositions (Russell et al., 1998); however, additional O-isotopic analyses conducted on Burnwell (Rumble III et al., 2007) gave a compositional value that clearly plots within the H chondriteOrdinary chondrites with a high content of free Ni-Fe metal (15-19 vol. %) and attracted easily to a magnet. Their main minerals are olivine (Fa16-20) and the orthopyroxene bronzite (Fs14.5-18.5), earning them their older name of bronzite chondrites. Chondrules average ~0.3 mm in diameter. Comparison of the reflectance spectra of Click on Term to Read More field.

Troiano et al. (2010, 2011) and Friedrich et al. (2011) studied a number of low-FeO chondrites with isotopic, mineralogical, and trace 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 values in the range of H chondrites, including Burnwell, EET 96031, LAP 04757/73, and MIL 07273. Their studies provide evidence for the origin of the low-FeO chondrites on the H chondrite 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. It is theorized that these low-FeO chondrites experienced extreme 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 processes in which an 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 Click on Term to Read More agent such as ice reacted with material containing a higher amount of metal than that present in typical H chondrites.

The low-FeO contents within this group of chondrites, as well as the variable abundances of metal and troilite, are considered by some to be primary features that were established early within the solar nebulaThe primitive gas and dust cloud around the Sun from which planetary materials formed. (McCoy et al., 1994). These properties were likely a consequence of the heterogeneous incorporation of nebular components within the parent body, rather than resulting from later parent body metamorphism. However, Mössbauer spectroscopyTechnique of splitting electromagnetic radiation (light) into its constituent wavelengths (a spectrum), in much the same way as a prism splits light into a rainbow of colors. Spectra are not smooth but punctuated by 'lines' of absorption or emission caused by interaction with matter. The energy levels of electrons in investigations indicate that 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 occurred in unequilibrated ordinary chondrites as metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. Click on Term to Read More grade increased, perhaps from progressive dehydration of phyllosilicatesClass of hydroxyl-bearing silicate minerals with a sheet-like structure. They result from aqueous alteration are dominantly serpentine and smectite in meteorites; found in the matrixes of carbonaceous chondrites. Phyllosilicates consist of repeating sequences of sheets of linked tetrahedra (T) and sheets of linked octahedra (O). The T sheet consists of Click on Term to Read More. This scenario would attribute the reduced nature of these ordinary chondrites to parent body processes rather than to the accretionAccumulation of smaller objects into progressively larger bodies in the solar nebula leading to the eventual formation of asteroids, planetesimals and planets. The earliest accretion of the smallest particles was due to Van der Waals and electromagnetic forces. Further accretion continued by relatively low-velocity collisions of smaller bodies in the Click on Term to Read More of primary low-FeO components on one or more unique parent bodies. However, no reducing agent such as C-rich material has been observed in these chondrites thus far.

Despite compositional and isotopic similarities with the low-FeO chondritic clasts in IIE irons such as Netshaëvo, the low 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. of Moorabie and other reduced unequilibrated ordinary chondrites are inconsistent with the highly metamorphosed character of the silicates in these irons. Therefore, the IIE parent body cannot be the parent body of the reduced ordinary chondrites. By the same token, no low-FeO clasts have been identified within H chondrite breccias, indicating that this is not the parent body either. These observations would suggest that this low-FeO group samples one or more unrecognized ordinary chondrite parent bodies. Resolution of the true origin of the reduced unequilibrated ordinary chondrites such as Moorabie will require further investigation.

Trapped 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 studies were conducted by Matsuda et al. (2010) on both a dark inclusionFragment of foreign (xeno-) material enclosed within the primary matrix of a rock or meteorite. Click on Term to Read More and a matrix sample from Moorabie. The trapped noble gas ratios in the dark inclusion were found to be similar to Q-type gases (‘Q’ for ‘quintessence’, including He, Ne, Ar, Kr, and Xe), while those from the matrix had a much lower abundance and a different composition. It was suggested that thermal metamorphism may be the cause of the lower abundance and different composition of Q 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 in the matrix.

It has been found that a positive correlation exists between petrologic type and 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".               Click on Term to Read More (Rubin, 2004). However, Moorabie is not typical of most other unequilibrated chondrites in that it is significantly shocked to stage S4–5. This is contrary to the expectation that a porous, volatile-rich, petrologic type-3 chondriteAn unequilibrated chondrite with a relatively unrecrystallized texture and containing mineral grains with heterogeneous compositions. would most likely be destroyed in an impact that resulted in a shock stage as high as S4–5. The Moorabie specimen shown above is a 49.4 g partial slice.