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NWA 960

Ordinary Chondrite, type 3, metal-poor
standby for nwa 960 photo
Purchased December 2001
no coordinates recorded A single stone weighing 997 g was found in Northwest Africa and purchased by A. and G. Hupé in Erfoud, Morocco. Samples were sent for analysis to the University of Washington, Seattle (A. Irving and S. Kuehner) and the Johnson Space Center, Houston (M. Zolensky). This meteorite contains mostly sub-mm-sized chondrules which are primarily olivine-rich, but a minor component of low-Ca pyroxene chondrules is present. It was determined that olivine and pyroxene have Fa and Fs values that lie outside of the range of the ordinary–rumurutiite chondrite clan. Minor mineral phases include magnetite, troilite, pentlandite, chromite and glass. FeNi-metal is absent, possibly due to its complete oxidation to magnetite.

In an effort to resolve the group to which this meteorite belongs, two separate labs were employed for oxygen isotope analysis—the University of Chicago (R. Clayton) and the Carnegie Institution, Washington D.C. (D. Rumble III). On an oxygen three-isotope diagram, the values plot outside of the field of the ordinary–rumurutiite chondrite clan, and after five years of study, it was decided that NWA 960 is best considered an anomalous, metal-poor, non-carbonaceous chondrite. Along with NWA 960, a small number of anomalous, ungrouped, non-carbonaceous chondrites have been studied and classified to date including HaH 180, NWA 2335, and NWA 2336, for which O-isotopic comparisons have been made to explore any possible genetic relationships (i.e., same parent body) among them. As shown on an oxygen three-isotope diagram, constructed by Achim Raphael, these meteorites plot very close to each other and might constitute a distinct field.

An additional small number of metal-poor, ungrouped non-carbonaceous chondrites have also been studied and classified to date, including the following members of the NWA-series: 2040 [LL], 2041 [L], 3114 [L], 3127 [LL], 3157 [L], 4294 [LL], 4298 [LL], 4486 [L], 4531 [LL], and 5717 [L+LL]). Oxygen isotopic analyses infer a possible ‘supra-TFL’ genetic grouping for these meteorites, which have a slope distinct from the ordinary chondrites (H, L, and LL) as illustrated on the oxygen three-isotope diagram below. standby for metal-poor oxygen plot
Diagram credit: Rumble III et al., 38th LPSC, #2230 (2007) See further details about this ‘supra-TFL’ grouping of meteorites on the HaH 180 page. Northwest Africa 960 is very weakly shocked to stage S1, and weathered to grade W1–2. The photo above shows a 5.2 g partial slice of this anomalous chondrite.

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Chondrite, ungrouped, type 3.5–3.8, low-FeO
(L3.8-an in MetBull 53)
standby for moorabie photo
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. Chondrules representing a large variety of types are closely spaced within a sparse white matrix. These chondrules exhibit foliation and preferential alignment, probably produced from an impact-shock event; Moorabie is shocked to stage S4–5. Olivine grains show undulatory extinction and mosaicism. Shock-heating also produced in situ local melting of some FeNi-metal and troilite 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 maskelynite are present in the matrix of Moorabie. Slow cooling followed the shock event.

Although Moorabie has been grouped with L-group chondrites, it forms a group of reduced chondrites (Fa1013) of mostly H-group association which might represent one or more unique objects distinct from the H, L, and LL ordinary chondrite parent bodies (Fa1620). 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 mineral compositions outside the established range for the known ordinary chondrite groups. Furthermore, their variable metal contents, low concentrations of Co in kamacite, 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 chondrite Burnwell is a fall that has similar low-FeO properties and which initially was shown to plot on an extension of the H–L–LL trend towards more reducing 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 chondrite field.

Troiano et al. (2010, 2011) and Friedrich et al. (2011) studied a number of low-FeO chondrites with isotopic, mineralogical, and trace element 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 body. It is theorized that these low-FeO chondrites experienced extreme redox processes in which an oxidizing 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 nebula (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 spectroscopy investigations indicate that reduction occurred in unequilibrated ordinary chondrites as metamorphic grade increased, perhaps from progressive dehydration of phyllosilicates. This scenario would attribute the reduced nature of these ordinary chondrites to parent body processes rather than to the accretion 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 type 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 gas studies were conducted by Matsuda et al. (2010) on both a dark inclusion 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 gases in the matrix.

It has been found that a positive correlation exists between petrologic type and shock stage (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 chondrite 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.

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HaH 180

Chondrite, Type 3.5-ungrouped
standby for hah180 photo
Found April 1996
28° 36.21′ N., 13° 18.04′ E. Six pieces of this highly unequilibrated meteorite were recovered in Ash Shati’, Libya, having a total combined weight of 936 g. The oxygen three-isotope diagram for HaH 180, constructed by Achim Raphael from published data, has values that plot slightly above the TFL and within a field occupied by a small number of anomalous, ungrouped, non-carbonaceous chondrites, including NWA 960, NWA 2335, and NWA 2336. Together with the NWA-series meteorites 2040 [LL], 2041 [L], 3114 [L], 3127 [LL], 3157 [L], 4294 [LL], 4298 [LL], 4486 [L], 4531 [LL], 5717 [L+LL; photo courtesy of Paul Swartz], NWA 7835 [ungrouped achondrite; Irving et al., 2014, #5332; photo courtesy of Stefan Ralew], and NWA 10769 [ungrouped achondrite; Moggi Cecchi et al., 2016, #2696], O-isotopic values infer a possible ‘supra-TFL’ genetic grouping for these meteorites which together plot along a slope distinct from the ordinary chondrites (H, L, and LL) on an oxygen three-isotope diagram. It is demonstrated in the diagram below that these meteorites plot far away from the trend lines for the H, L, and LL ordinary chondrite groups, and they probably represent several previously unrecognized parent asteroids (Irving et al., 2014, #5332). standby for metal-poor diagram
Diagram credit: Rumble III et al., 38th LPSC, #2230 (2007) The mineralogy of HaH 180 consists of olivine and Fe-rich pyroxene and excludes a relationship with E chondrites. This meteorite is very weakly shocked to stage S2 and highly weathered to grade W4. Studies of the bulk chemical and mineral composition and petrographic features of both HaH 180 and the similar Deakin 001 suggest an affinity to LL-group chondrites. The anomalously high 18O compositions could be explained by unusually high terrestrial weathering effects, or that these unequilibrated ordinary chondrites sample a wider range of oxygen isotope compositions than previously identified. On the other hand, these meteorites might represent a unique chondritic parent body. Interestingly, a dark inclusion found in the LL3.3 chondrite Wells has an O-isotope composition that plots close to HaH 180, as does a silica-rich orthopyroxenite inclusion found in the L3 chondrite Bovedy.

The HaH 180 specimen shown above is a 5.5 g cut fragment exhibiting a characteristic large, rounded, dark-rimmed, lithic clast. Below is an in situ photo of HaH 180, its persistent dark appearance belying a long terrestrial residence. A high-resolution photo of a 7.73 g full slice of one of the smaller HaH 180 fragments is an exquisite sight.

standby for hah 180 in situ photo