Ungrouped Primitive Achondrites


There are several unusual primitive achondrites that apparently are not related to the lodranite-acapulcoite or brachinite parent bodies. Divnoe and Zag (b) are two FeO-rich achondrites that are similar to brachinites, but with different oxygen isotope patterns. NWA 3133 and 1839 specimens were originally classified as L7 chondrites, but oxygen isotope analyses show that these meteorites are primitive achondrites whose oxygen isotopes plot on the CV3 mixing line and may represent melt differentiates of a moderately large CV3 parent body. NWA 011/2400 (see classification below) is very different from other primitive achondrites in having FeO/MnO molecular ratios similar to lunar rocks and oxygen isotopes consistent with CR carbonaceous chondrites. Moreover, the texture is consistent with igneous derivation in contrast with the metamorphic recrystallized textures of most primitive achondrites. Like NWA 3133 and 1839, this meteorite may also be an igneous melt differentiate of a moderately large CR carbonaceous chondrite parent body.

Divnoe. Cross polarized light (XPL) image showing strong preferred orientation of mostly olivine grains. Base width = 3 mm.

NWA 3133. Highly recrystallized texture in XPL. Base width is 2 mm.


Northwest Africa 1982

Morocco
Found 2000
Achondrite (ungrouped)

A 368 g partially crusted stone was purchased in Rissani in 2001. Classification and mineralogy (T. Bunch and J. Wittke, NAU): cataclastic pyroxenite with randomly dispersed metal grains; partial recrystallization of matrix and along fractures of large (up to 5 mm) orthopyroxene grains. Mineral modes: orthopyroxene, 68 vol%; metal, 12 vol%; plagioclase, 8 vol%; troilite, 3 vol%; ilmenite, 3 vol%; phosphate, 2 vol%; spinels, 2 vol%; and augite 2 vol%. Orthopyroxene, Fs28Wo3; kamacite, Ni = 4.8 to 5.4 wt%; taenite, Ni = 31.4 to 36.7 wt%; plagioclase, An90; spinel #1, Al2O3 = 61 wt%, MgO = 21.4 wt%, FeO = 13.2 wt%; spinel #2, Cr2O3 = 35.9 wt%, Al2O3 = 33.0 wt%, MgO = 17.9 wt%, FeO = 13.1 wt%; augite, Fs13Wo43. Oxygen isotope composition is somewhat outside the range of HED and closest to brachinites and IAB-IIICD irons (R. N. Clayton, UChi): δ18O = +3.78 per mil., δ17O = +1.47 per mil, Δ17O = +3.78 per mil. Cosmic ray exposure age (O. Eugster, UBE) of 18.6 ± 2.0 Ma falls on the major CRE cluster of the HED meteorites. Not paired with NWA 1827 or 1879 mesosiderite C. Shock level, S1. Weathering grade, W1. Specimens: type specimens: 13.8 g, NAU, 11.5 g with O. Eugster, UBE; main mass, Fectay.


Northwest Africa 2195

Northwest Africa
Find: 2005
Achondrite (primitive achondrite, ungrouped)

History and physical characteristics: A 369 g single, stone was purchased from a dealer in Erfoud, Morocco in 2004 by Dr. David Gregory. The dark brown stone is fully crusted with light to moderate desert ablation with minimal surface chemical weathering.
Petrography (T. Bunch and J. Wittke. NAU): A fine-grained (<0.3 mm) recrystallized stone of essentially equigranular olivine and Cr-diopside that displays an unusual example of poikioblastic texture. Cr-diopside oikiocrysts contain small (< 0.03mm) olivine chadacrysts. Mineral modes (in vol%): all olivine, 56; Cr-diopside, 42, metal and FeS, 2. Most metal has oxidized.
Mineral compositions: Olivine grains and chadacrysts, Fa12.3-12.6; Cr2O3 = 0.51 to 0.65 wt%; CaO = 0.28 wt%; FeO/MnO = 22. Cr-diopside, Fs6.0Wo39.0; Cr2O3 = 1.35 wt%; Al2O3 = 1.25 wt%; FeO/MnO = 10. Metal Ni = 0.7 to 1.3 wt%.
Oxygen isotopes (D. Rumble, CIW): a cleaned and metal-free sample was analyzed by laser fluorination. Replicate analyses are, respectively, δ17O = 2.556, 2.570; δ18O = 6.016, 6.618; Δ17O = -0.608, 0.911 (all ‰).
Classification: Achondrite (primitive achondrite, ungrouped). Although NWA 2195 olivine composition and FeO/MnO ratio are somewhat consistent with the lodranite/acapulcoite family, oxygen isotopes and the Fa vs. Δ17O ratio are slightly different. In addition, NWA 2195 lacks orthopyroxene and contains very little metal. We suggest that this stone be classified as a primitive achondrite, ungrouped.
Type specimen: A total of 20.1 g is on deposit at NAU. Dr. David Gregory is the main mass holder.

NWA 2195. Image width 14 mm. Image © T. E. Bunch, 2008.


Northwest Africa 2400

Morocco or Algeria
Purchased April 2003
Achondrite (ungrouped)

A 137 g light tan to rusty brown, fully crusted stone was purchased in Rissani, Morocco in April 2003. Description and classification (T. Bunch and J. Wittke, NAU; A. Irving and S. Kuehner, UWS): composed mainly of approximately mm-sized, randomly oriented pigeonite (Fs64-64.8Wo5.6-6.4) with very fine, parallel exsolution lamellae of augite (Fs38-49.1Wo36.7-23), and interstitial, recrystallized plagioclase (<0.10 mm in size, ~An86Or0.5) with prominent triple junctions, and rare, unrecrystallized, tabular plagioclase relicts (<1 mm, zoned from An80to An89). FeO/MnO ratios for all pyroxenes range from 59.5 to 68.7 (average = 64.7). Only small amounts of pyroxene are present in the recrystallized zones. Accessory minerals occurring predominantly in the recrystallized plagioclase zones include a silica polymorph, chromite [Cr/(Cr + Al) = 0.83, Fe/(Fe + Mg) = 0.67], ilmenite (53.5 wt% TiO2, 43.6 wt% FeO; with small baddeleyite inclusions), merrillite (some with minor amounts of Na2O, MgO, and FeO), Zn-bearing troilite, pentlandite, Cr-ulvöspinel and altered Fe metal (associated with minor troilite, barite and calcite). Shock damage is not apparent and, with the exception of the oxidation of minor metal, weathering effects are very low. Oxygen isotopes (D. Rumble, CIW): replicate analyses by laser fluorination gave δ17O = - 0.15 ± 0.1, δ18O = 3.27 ± 0.2, Δ17O = -1.57 ± 0.03 per mil. In its texture, mineral mode, mineral compositions and oxygen isotope composition NWA 2400 is nearly identical to the non-Vesta anomalous achondrite NWA 011 (Yamaguchi et al., 2002; Promprated et al., 2003), which strongly indicates that these two stones are paired. Specimens: type specimen 20.2 g and three polished thin sections, NAU; main mass, anonymous purchaser.

NWA 2400. Plane-light photograph of olivine phenocrysts surrounded by recrystallized plagioclase, pyroxene, and some olivine. Large white grain is relict plagioclase. Base width = 5 mm.

NWA 2400. Olivine grains surrounded by recrystallized plagioclase, pyroxene, and olivine. Base width is 2.5 mm. XPL.

References

Yamagouchi A., Clayton R. N., Mayeda T., Ebihara M., Oura Y., Miura Y. N., Hjaramura H., Misawa K., Kolima H. & Nagao K., 2002, A new source of basaltic meteorites inferred from Northwest Africa 011, Science 296, 334-336.

Promprated P., Taylor L. A., Anand M., Rumble III D., Korochantseva E. V., Ivanova M. A., Lorentz C. A. & Nazarov M. A., 2003, petrology and oxygen isotopic compositions of anomalous NWA 011. In Lunar and Planetary Science XXXIV. Lunar and Planetary Institute, Houston, TX (CD-ROM), Abstract 1757.


Northwest Africa 2635

Northwest Africa
Purchased October 2004
Achondrite (ungrouped)

A 4.2 kg, partially crusted stone was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU), results from one thin section (2.4 cm2): mostly recrystallized into fine-grained (<0.5 mm, avg. = 0.185 mm) polygonal and subhedral grains with the exception of several medium to large (1.2-3.0 mm) orthopyroxene grains that contain very small olivine (<0.1 mm) inclusions. Very homogeneous assemblage, olivine and orthopyroxene analyses are within the precision of the electron microprobe (± 0.15 mol %). Olivine, Fa18.9 (FeO/MnO = 38.1); orthopyroxene, Fs16.8Wo2.9 (FeO/MnO = 20.0); plagioclase, An15.1Or4.7; metal (only taenite found), Ni = 18.9 wt%; chromite (only one grain found), Cr/[Cr+Al] = 84.5; FeS, Ni = 1.42 wt% and Co = 0.28 wt%, minor merrillite. Oxygen isotope replicate analyses (D. Rumble, CIW) of acid washed, bulk sample by lased fluorination gave δ17O = 3.23 and 2.98, δ18O = 5.03 and 4.37 and Δ17O = 0.614 and 0.708. Formerly classified as an H7. Weathering grade, W2/3 with staining; shock level, S1. Specimens: type sample, 23.2 g, NAU; main mass, Strope/Farmer.

NWA 2635. Image © T. E. Bunch, 2008.


Northwest Africa 2907

Northwest Africa
Found 2005
Achondrite (ungrouped)

History: A large number of pieces were collected within a small strewn field of ~15 m diameter in Algeria and sold in Erfoud, Morocco.
Physical characteristics: Most of the 586 g mass of fragments are without fusion crust, are dark brown in color and show extensive surface weathering.
Petrography (T. Bunch and J. Wittke, NAU): partially recrystallized polymict breccia that contains at least two distinct lithologies: (A) medium-grained clasts (< 2mm) of untwinned orthopyroxene without discernable exsolution lamellae and a roughly equal amount of complex, polysynthetically twinned plagioclase partially converted to maskelynite and (B) medium-grained, partially recrystallized pigeonite with minor development of exsolution lamellae and twinning with inclusions of simple, albite-twinned plagioclase together with a fine-grained assemblages (< 0.1 mm) of tridymite, metal, and plagioclase at recrystallization boundaries. Both lithologies are set in a fine-grained, partially recrystallized matrix of pyroxenes and plagioclase compositionally similar to lithologies A and B. Minor minerals include Al-rich chromite, sulfide, tridymite, phosphate and metal.
Geochemistry: lithology (A) orthopyroxene cores are Fs22.0-25.3Wo2.5 and the FeO/MnO = 24-27and have replacement grain margins of Fs33.8Wo7.2 that in turn have exsolved Ca-rich pyroxene, Plagioclase composition is An99.5Or0.5. Lithology (B) pigeonite is Fs38.1Wo11.1 and the plagioclase is An94.8Or5.6..
Classification: Achondrite (ungrouped). Overall characteristics of this meteorite are similar to clast material in some mesosiderites and may represent a large, separated mesosiderite clast. Shock level is S3 (maskelynite threshold) and the stone is moderately weathered.
Type specimens: A total of 23g are on deposit at NAU. Mr. Blaine Reed holds the main mass.

Reference

Irving, A. J., Bunch, GT. E., Rumble, III, D. & Larson, T. E., 2005, Metachondrites: Recrystallized and/or residual mantle rocks from multiple, large chondritic parent bodies: 68th Meteoritical Society Meeting, #????.


Northwest Africa 2968

Northwest Africa
Find: 2004
Achondrite (ungrouped)

History and physical characteristics: A bag of rectangular to blocky, dark brown meteorite fragments, with a total mass of 268 g and collected by nomads in 2004, was purchased in Erfoud, Morocco, in November 2005.
Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS) A massive olivine-rich rock of very large grain size (17 to >25 mm; maximum size is unknown because of the tendency to fracture on cutting). Curved to linear compression and shear fractures are subparallel to one of the extinction directions in olivine and are responsible for the common rectangular/blocky habit. Twenty-three pieces (1.8 to 20.1 g) were surveyed. Olivine accounts for >95 vol% with small amounts of tiny grains (<0.03 mm) of orthopyroxene, metal, troilite, and pyrrhotite commonly found within fractures and as rare inclusions in olivine. Large domain offset, isolated mosaicism, and undulatory extinction are prevalent in olivine.
Mineral compositions and geochemistry: Equilibrated olivine (Fa7.5±0.2; FeO/MnO = 48; Cr2O3 and NiO <0.03 wt%), orthopyroxene (Fs6.7Wo1.5; FeO/MnO = 26), kamacite (Ni = 4.7–6.8 wt%), taenite (Ni = 39.1–50.7 wt%), troilite (Ni = 0.36 wt%), pyrrhotite (Ni = 1.7–4.7 wt%). Oxygen isotopes: (D. Rumble, CIW) Analysis of two cleaned and metal-free samples by laser fluorination yielded "δ17O = 1.44, 1.46; δ18O = 3.08, 3.64 and Δ17O = -0.178, -0.212 (all ‰).
Classification: Achondrite (ungrouped).
Type specimen: A 22 g sample is on deposit at NAU. Reed holds the main mass.


Northwest Africa 2976

Northwest Africa
Find: 2005
Achondrite (ungrouped)

History and physical characteristics: A complete 219 g stone with no crust was purchased in Erfoud, Morocco, in November 2005.
Petrography: (T. Bunch and J. Wittke, NAU) Contains millimeter-size pigeonite with exsolved augite lamellae surrounded by recrystallized plagioclase and minor amounts of relict plagioclase of similar composition.
Mineral compositions: Pigeonite (Fs64.8Wo6.1), FeO/MnO = 64; augite (Fs44.2Wo27.3); plagioclase (An84.0-86.8). Abundant chromite is observed. The sample also contains minor amounts of Zn-bearing FeS, Cr-ulvöspinel, silica, and phosphate.
Classification: Achondrite (ungrouped); minimal shock and weathering. This meteorite is paired with NWA 2400 and NWA 011. Although no oxygen isotopic data have yet been obtained, the petrography is essentially identical to these two meteorites.
Type specimen: A 23.2 g sample is on deposit at NAU. Farmer and Strope hold the main mass.

NWA 2976. The polished cut surface of a hand sample of NWA 2976, with the longest axis ~4 cm. Image © T. E. Bunch, 2008.


Northwest Africa 2993

Algeria
Find: 2006
Achondrite (ungrouped, lodran-like)

History: A fully crusted, complete stone of 625 g was recovered from the lower Algerian desert in June 2006 and purchased in Erfoud in August 2006 by A. Aaronson.
Petrography (T. Bunch and J. Wittke, NAU; T. Irving, UWA): Protogranular texture with a grain size range of 0.3-3.4 mm (mean = 1.35 mm) for silicates and 0.3 to 5 mm for metal (mean = 2.4 mm). Modal analyses (6.4 cm2; vol%): orthopyroxene, 37; olivine, 32; metal, 30; sulfide, 1. Several metal grains have taenite cores mantled by kamacite. Taenite grain shape is roughly similar to the outline of the entire metal grain; embryonic plessite is evident in a few taenite cores. No directional fabric was recognized. Fusion crust is lightly to moderately altered and weathering is limited to minor oxidation of kamacite with the presence of minor oxide veining.
Geochemistry: Olivine, Fa12.3±0.2, FeO/MnO = 32; orthopyroxene, Fs11.2±0.02Wo1.2, FeO/MnO = 19; taenite, Ni = 7.9 wt%; kamacite, Ni = 4.6 wt%.
Oxygen isotopes (D. Rumble, CIW): A cleaned and metal-free sample was analyzed by laser fluorination. Replicate analyses are respectively, δ17O = 1.129 and 1.220; δ18O = 2.527 and 2.661; Δ17O = -0.2006 and -0.1802 (all ‰).
Classification: Achondrite, ungrouped lodran-like. Petrography and geochemistry are consistent with lodranites, oxygen isotopes are inconsistent with lodranites/acapulcoites and are closest to the 1AB irons and winonaite trend.
Specimens: 20.3 g and one polished thin section are on deposit at NAU. The main mass holder is anonymous.

NWA 2993. Cut face; width = 3.3 cm. Image © T. E. Bunch, 2008.

NWA 2993. Base width = 9 mm. Image © T. E. Bunch, 2008.


Northwest Africa 4284

Algeria
Find: 2005
Achondrite (anomalous)

History: This partial stone was found in 2005 and purchased in Erfoud, Morocco in October 2005.
Physical description: The exterior is dark brown where not covered by moderately weathered fusion crust. The total weight is 137g.
Petrography (T. Bunch and J. Wittke, NAU): Igneous textures include hypidimorphic-granular, ophitic, and poililitic (orthopyroxene oikocrysts enclose olivine). NWA 4284 is composed of mm to sub mm-sized grains of (in order of abundance) orthopyroxene, olivine, plagioclase, diopside, FeS, and chromite. Taenite metal is relegated to rare, isolated clusters of coarser-grained orthopyroxene-olivine-plagioclase-taenite.
Geochemistry: Orthopyroxene, Fs24.5Wo3.5, FeO/MnO = 28-30; olivine, Fa24.6, FeO/MnO = 46-54; plagioclase. An11Or5.3; diopside, Fs8.2Wo44.2; chromite, Cr/[Cr+Al] = 0.88; and taenite, Ni = 21.5 wt % (no kamacite was found).
Oxygen isotopes (D. Rumble, CIW): a cleaned and metal-free sample was analyzed by laser fluorination. Replicate analyses are, respectively, δ17O = 3.253, 3.227; δ18O = 4.195. 4.247; Δ17O = 1.046, 0.993 (all ‰).
Classification: Achondrite, (anomalous). Mineral compositions and oxygen isotopes indicate that this stone has an L chondrite heritage, but the lack of chondrules and obvious igneous textures, indicate a late melting event. Lightly weathered and lightly shocked (S2).
Type specimens: A total of 21 g and one thin section are on repository at NAU. Mr. Edwin Thompson is the main mass holder.

NWA 2484. A partial, cross-polarized image that illustrates protogranular igneous texture. Width = 7 mm. Image © T. E. Bunch, 2006.

NWA 2484. BSE image. Bright = chromite and FeS; dark gray = plagioclase; medium gray = orthopyroxene; dark gray = olivine. Image © J. H. Wittke, 2006.


Northwest Africa 5784

Morocco
Find: Purchased 2008
Achondrite (ungrouped)

History and physical characteristics: A single 2.6 kg, dark brown stone was purchased in February 2008 from a Moroccan dealer at the Tucson Gem and Mineral Show by Blaine Reed.
Petrography (T. Bunch and J. Wittke, NAU): A cataclastic dunite that contains (in vol%) olivine, 91; plagioclase, 5; orthopyroxene, 2; chromite and Fe-metal, 2. Severe crushing is prevalent throughout the rock; many of the olivine and plagioclase fragments show mottled extinction. Finest grain size domains are recrystallized. Slight staining around tiny metal grains was observed.
Geochemistry: Olivine (Fa31.3; FeO/MnO = 34); plagioclase (An94.5); chromite, Cr/(Cr+Al) = 0.70); metal (Ni = 0.35 wt%). Oxygen isotopes (D. Rumble, CIW): Replicate analyses of acid-washed whole rock samples by laser fluorination gave, respectively, δ18O = 3.56, 3.10; δ17O = 1.67, 1.39; Δ17O = -0.205, -0.243 per mil.
Classification: Achondrite (ungrouped). Mineral compositions and oxygen isotopic composition suggest affinity with diogenites.
Type specimen: A total of 20.6 g is on deposit in the PSF collection at FMNH. Mr. Blaine Reed holds the main mass.

NWA 5784. Cross-polarized light image. Bright colors are olivine; the large white patch right of center is plagioclase. Field of view is 9 mm wide. Image © T. E. Bunch, 2010.


Northwest Africa 5968

Morocco
Find: 2008
Achondrite (ungrouped)

History and physical characteristics: A 15.5 g partially crusted, dark brown stone was found in a bag of unclassified specimens that was purchased in Erfoud, Morocco.
Petrography (T. Bunch and J. Wittke, NAU): A massive dunitic rock of large grain size (>31 mm x 14 mm, larger because only a portion of the grain is present). A sub-parallel set of compression fractures cross-trend a second set of annealed shear fractures that contain tiny, recrystallized olivine grains. The entire olivine mass is highly charged with clear, submicron inclusions of indeterminate composition. Scattered patches of planar deformation features and minor undulatory extinction suggest a moderate shock level.
Mineral composition: Olivine (Fa8.8; FeO/MnO = 29).
Classification: Achondrite (ungrouped). The olivine composition suggests an affinity with highly magnesian olivine diogenites.
Type specimen: A total of 4.4 g is on deposit at NAU. The main mass holder is anonymous.

NWA 5968. Bulk sample. Rock is 32 mm wide. Image © T. E. Bunch, 2010.

NWA 5968. Cross-polarized light image of large olivine. Field of view is 23 mm wide. Image © T. E. Bunch, 2010.


Northwest Africa 6698

Morocco
Find: 2009
Achondrite (ungrouped)

History: A 38.4 g stone found October 2009 was purchased from a dealer in Erfoud, Morocco in 2010.
Physical description: No remaining fusion crust. Surface is lightly weathered, but heavily desert wind-ablated.
Petrography (T. Bunch and J. Wittke, NAU; A. Irving, UWS): Fine to medium grained (<2mm) dioritic rock that contains 69 vol% plagioclase, 27 vol%, pyroxenes (augite and pigeonite), and 4 vol% accessory phases (taenite, chromite, chlorapatite and FeS). Plagioclase displays simple albite and Carlsbad twinning, is mostly equigranular, and contains included pyroxene chadacrysts. Pyroxenes are dominantly augite and unexsolved pigeonite with highly variable grain size, and contain included plagioclase chadacrysts. Sparse pockets of brown, glassy late stage residuum with microlites are present between the other phases. Shock level is low to moderate, with undulatory extinction in plagioclase and some pyroxenes. Interior weathering is low.
Geochemistry: Most plagioclase ranges in composition from An22.4 to An36; a few zoned grains have cores of An52-56Or2.1 and rims of An36; residuum albite, An10Or5.7. Augite, Fs18.5-27.0Wo36.7–41.2 (FeO/MnO = 14-17), Al2O3 = 2.2 wt%, Na2O = 1.2 wt%; TiO2 = 1.23 wt%; Cr2O3 = 1.55 wt%. Pigeonite, Fs34.4-39.7Wo8.6-14.5 (FeO/MnO = 20), Al2O3 up to 3.2 wt%. Taenite (Ni = 27.7 wt%), chromite (cr# = 0.90), and FeS (Ni = 1.58 wt%). Residuum glass (wt%): SiO2, 70; Al2O3, 13.8; Na2O, 9.4; K2O, 2.9; CaO 2.1; FeO, 2.8. Oxygen isotopes (D. Rumble, CIW): Replicate analyses of acid-washed whole rock samples by laser fluorination gave δ18O = 4.80, 4.73; δ17O = 3.72, 3.75; Δ17O = 1.199, 1.265 (all ‰).
Classification: Achondrite (ungrouped). Mineralogy and mineral chemistry are unlike those of any other known achondrite, and the oxygen isotopic composition plots well above the TFL in the field for LL chondrites.
Specimens: A total of 7.7 g of material including one polished thin section are on deposit at NAU. Mr. A. Habibi holds the main mass.


Other Ungrouped Achondrites

IDLocationDateClass.Mass (g)StateOlivonePyroxeneComments
NWA 2653Zagora, Morocco2004ACHOND189S1, W4Fa28.5 (FeO/MnO = 65.2) Fs23.3Wo8.0 (FeO/MnO = 48.2)paired with NWA 3133