Ureilites

Dhofar 979 (19°45.4' N, 54°56.2' W)

Oman
Found 2004
Achondrite (ureilite)

A completely fresh, crusted stone of 1063 g was found by Michael Farmer in the Dhofar region of Oman on January 8, 2004. Description and classification (T. Bunch and J. Wittke, NAU): medium-grained typical ureilite with very fine-grained, wormy graphite at grain boundaries and included within olivine and pigeonite. Very low reduction level or “smelting” activity (R1); graphite mostly intact. Olivine cores, Fa_16.5 (FeO/MnO = 36 g/g) and rims, Fa_15.8; pigeonite, Fs_14.9Wo_5.0. Very little metal and terrestrial Fe-oxides present. Shock level, S1 and lightly weathered. Specimens: type sample, 44.7 g, NAU: main mass, Farmer.

Dho 979. (left) Typical ureilite texture of Dho 979 with an R1 reduction level. Note tiny, wormy graphite at grain boundaries and included within olivine. Blue-gray color denotes scarce areas of reduction. Partial plane polarized light combined with partial reflected light that highlights the altered reduced areas of olivine and pigeonite by imparting a blue-gray hue. (right) Cross polarized light image of same sample. Image ©; T.E. Bunch, 2005

Northwest Africa 771 (26°33.60' N, 11°33.33' W)

Morocco
Found 2000 June
Achondrite (ureilite)

A 313 g stone was found near Nebca, Morocco, by a person prospecting for meteorites. Mineralogy and classification (T. Bunch and J. Wittke, NAU): has typical ureilite texture; contains reversely zoned olivine (Fa_12-17; Cr = 0.7 wt. %) and pigeonite (Fs₁₇Wo₁₀); average metal composition, Ni = 3.3 wt. %, Si = 1.6 wt. %, Cr = 0.25 wt. %; troilite contains up to 9 wt. % Cr and 1 wt. % Ni; shock stage, S2; weathering grade, W1. Specimens: 21.2 g plus thin section, NAU; main mass with anonymous finder.

NWA 771. Image width 13 mm. Image © T.E. Bunch, 2005

Northwest Africa 1569

Morocco
Found 2000
Achondrite (ureilite)

A 614 g partially crusted stone was purchased in Erfoud, Morocco in 2001. Classification and mineralogy (T. Bunch and J. Wittke, NAU): typical ureilite texture; olivine grain size up to 1.5 mm with triple junctions, poorly developed lineation, low-Ni metal (mostly oxidized) interstitial to olivine; low-Ca pyroxene is <1 mm and tends to occur in clusters with interstitial carbonaceous matter. Olivine cores are Fa₁₈, dusty rims are reduced to Fs₁₀; (Cr₂0₃ up to 0.62 wt. %; CaO up to 0.41 wt.%); 1ow-Ca pyroxene is Fs_l8Wo₈ to Fs₂₃Wo₉; metal, 0.47 to 5.3 wt.% Ni, 0.55 wt. % Cr₂0₃, 0.4 wt. % P and 0.29 wt.% Si; sulfides contain up to 1.4 wt. % Cr. Shock level, S2; weathering grade, W1. Specimens: main mass with anonymous buyer; type specimen, 20.5 g, and thin section, NAU.

Northwest Africa 1834

Morocco
Found 2002
Achondrite (ureilite)

A 20.17 g stone was purchased in Rissani, Morocco in 2003. Classification and mineralogy (J. Wittke and T. Bunch, NAU): typical, medium to fine-grained (<2 mm) ureilite, non-foliated, and with only thin (0.0i5 mm) reduced rims on olivine and pigeonite. Interstitial metal (Ni = 2.92 wt. %; Co, 0.51 %; Si, 2.4 %) is partially oxidized. Millimeter-size graphite occurs at grain boundaries of main phases and contains silica platelets (< 3 µm) and clusters of sulfide and schreibersite. Olivine Mg/(Mg+Fe) = 0.88 with 0.87 wt. % Cr₂O₃ and 0.57 % CaO; pigeonite Mg/(Mg+Fe) = 0.88 and contains up to 1.0 wt. % Cr₂O₃. Shock level, S2 and only slightly weathered. Specimens: 4.2 g at NAU; main mass, Oakes.

NWA 1834. Typical ureilite; reduction level is R1; (left) dark grains are graphite. Plane polarized light, base width = 8 mm. (right) Same sample, cross-polarized light. Image © T. E. Bunch, 2005

Northwest Africa 1841

Morocco
Found 2003
Achondrite (ureilite)

A 39.3 g, complete and fully crusted stone was purchased in Rissani, Morocco June 2003. Description and classification (J. Wittke and T. Bunch, NAU): typical ureilite with prominent development of carbonaceous/reduced material along internal fractures and (001) planes of olivine, in addition to typical interstitial areas. Olivine cores, Fa_21.8 (Cr₂O₃ = 0.78 wt. %, rims, Fa_8.2-0.8 (Cr₂O₃ = 0.80 wt. %); pigeonite, Fs_18.3Wo₈; olivine metal inclusions, Ni = 0.92 wt. %; interstitial metal, Ni = 4.45 wt. %, Si = 0.57 wt. %. Shock level, S2; low degree of weathering. Specimens: 8.4 g, NAU; main mass, Oakes.

Northwest Africa 1913

Morocco
Found 2001
Achondrite (ureilite)

A 731 g complete and partially crusted stone was purchased in Erfoud in 2002. Classification and mineralogy (T. Bunch and J. Wittke, NAU): typical ureilite texture with preferred orientation of elongated silicates. Mineral modes (vol. %): olivine, 68 and pigeonite, 32. Olivine cores, Fa_19.2-19.6 and reduced rims, Fa_1.5-3.0. Pigeonite, mostly Fs₁₇Wo₁₁. Metal along grain boundaries is 9.3 wt. % Ni; and metal together with pyrrhotite as inclusions in pigeonite is 3.6 wt. % Ni. Carbonaceous matter at grain boundaries, no evidence of diamonds. Shock level, S1; weathering grade, W2. Specimens: type specimen, 21.2 g, NAU; main mass, Boswell.

NWA 1913. (left) Plane light photomicrograph of a typical ureilite; reduction level, R2; base width is 5 mm. (right) Same sample, cross-polarized light. Image ©; T. E. Bunch, 2005

Northwest Africa 1926

Morocco
Found 2003
Achondrite (ureilite, polymict)

NWA 1926. Image ©; T. E. Bunch, 2004

A 36.8 g partial stone was purchased in Rissani June 2003. Classification and mineralogy (J. Wittke and T. Bunch, NAU): fragmental breccia with clasts of a poikilitic ureilite embedded in typical ureilite materials that consists of olivine with homogeneous cores (Fa₃₁) and reduced rims (Fa_2-7) and pyroxenes with Fs_19.7Wo_4.5 in cores and Fs_9.5Wo₁ at rims. Heavy concentration of carbonaceous matter; unoxidized metal, Ni = 2.95 wt. %. Clasts are composed of large pyroxenes (Fs_19.1Wo_4.0) that poikilitically enclose homogeneous olivine (Fa_21.8). Clast ureilite contains very little carbonaceous matter in contrast to the host ureilite. Shock level, S2; low degree of weathering. Specimens: type specimen, 6.3 g, NAU; main mass, Farmer.

NWA 1926. Poikilitic typical ureilite (small olivine grains included in much larger pigeonite, gray). Cross-polarized light photomicrograph; base width is 2.5 mm. Image ©; T. E. Bunch, 2004

Northwest Africa 2082

Morocco
Found 2003
Achondrite (ureilite)

NWA 2082. Image ©; T. E. Bunch, 2004

A 33 g single, complete stone was purchased in Rissani, Morocco in October 2003. Description and classification (J. Wittke and T. Bunch, NAU): typical ureilite with a large amount (~30 vol. %) of dark, interstitial materials (carbon, fine-grained silicates, and weathering oxides). Olivine cores are Fa_17.8 (Cr₂O₃ = 1.03 wt %); reduced rim olivine, Fa₄ (Cr₂O₃ = 0.73 wt %); pigeonite cores, Fs_15.6Wo_6.2 (Cr₂O₃ = 1.21 wt. %), rims, Fs_10.1Wo_8.6 (Cr₂O₃ = 0.93 wt. %). Shock level, S2; weathering grade, medium (no metal or sulfides remain). Specimens: type sample, 8.5 g, and one thin section, NAU; main mass, Farmer.

Northwest Africa 2088

Morocco
Found 2003
Achondrite (ureilite)

A single complete stone of 252 g was purchased in Rissani, Morocco in November 2003. Description and classification (T. Bunch and J. Wittke, NAU): typical ureilite of low metamorphic grade; contains graphite flakes and limited development of silicate rim reduction and interstitial metal. No evidence of preferred grain orientation. Pigeonite shows pronounced {100} lamellar twinning. Olivine cores, Fa_10.3, rims Fa_7.8; pigeonite, Fs_9.1Wo_7.3. Shock level, S3; weathering grade, W2. Specimens: 20.7 g, and one thin section, NAU; main mass, Farmer.

Northwest Africa 2352

Northwest Africa
Found 2003
Achondrite (ureilite)

A complete, dark brown and partially crusted stone of 389 g was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): high amounts of large, laminated graphite grains (up to 1.9 mm in length) occur interstitially to olivine and pigeonite; only small amounts of carbonaceous-metal-silicate masses (CMSM) are present. Very limited olivine rim reduction or smelting, R1 level with less that 0.02 mm of olivine margins affected. Olivine cores, Fa_11.9 (FeO/MnO = 21 g/g) and rims are Fa_10.7 (FeO/MnO = 19 g/g); pigeonite. Fs_11.4Wo_9.4 (FeO/MnO = 13.7 g/g). Oxygen isotopes (D. Rumble, CIW): replicate analyses by laser fluorination gave δ¹⁷O = 2.86 and 2.89, δ¹⁸O = 7.16 and 7.37 and Δ¹⁷O = -0.913 and -1.002 per mil. Very lightly weathered in the interior with low-level shock (S2). Specimens: type sample, 21.1 g, NAU: main mass, Regelman.

NWA 2352. Typical ureilite, medium-grained; R2; cross-polarized light; base width = 7 mm. Image ©; T. E. Bunch, 2005

NWA 2352. Large (2.4 mm), optically twinned pigeonite pyroxene with included grains of olivine. Cross-polarized light. Image ©; T. E. Bunch, 2005

Northwest Africa 2374

Northwest Africa
Purchased 2004 August
Achondrite (ureilite)

A single stone of 31.5 g was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): typical ureilite, fine to medium-grained with a high degree of preferred orientation of mafic silicates. High abundance of laminar, interstitial graphite with low abundance of metal (and weathered oxides); graphite to metal ratio = 8:1 (vol. %). Low level of silicate reduction (R2): reduced olivine rims are lightly affected (< 0.02 mm or <10 vol. %), pigeonite only marginally affected. Olivine cores, Fa_21.0 (FeO/MnO = 39 g/g), Cr₂O₃ = 0.80 wt. %, rims = Fa_12.9. Pigeonite, Fs_18.1Wo_7.9(FeO/MnO = 31 g/g). Low weathering grade and lightly shocked. Specimens: type specimen, 6.7 g, NAU; main mass, Birdsell.

NWA 2374. (left) Typical ureilite that shows preferred orientation of olivine and pigeonite. R2; Plane polarized light, base width = 7 mm. (right) Same sample, cross-polarized light. Image ©; T.E. Bunch, 2005

Northwest Africa 2376

Northwest Africa
Purchased 2004 August
Achondrite (ureilite)

A single stone of 123 g was purchased in Erfoud, Morocco. Description and classification (J. Wittke and T. Bunch, NAU): typical ureilite that mostly consists of medium to coarse-grained olivine and pigeonite. Extensive reduction (R5) has affected more than 60 vol. % of all olivine and ~15 vol. % of pigeonite. Carbonaceous-metal-silicate masses (CMSM) are also extensively developed. Olivine cores, Fa_12.3 (FeO/MnO = 19 g/g), Cr₂O₃ = 0.60 wt. %; olivine rims, down to Fa_1.2; pigeonite cores, Fs_10.9Wo_5.2. Also, interstitial Al-rich augite, K-rich glass, Fe₃C, and probable diamond. Interstitial metal is mostly weathered to various iron oxides; no observable primary graphite. Low weathering grade and lightly shocked (S2). Specimens: type sample, 21.1 g, NAU; main mass, Birdsell.

NWA 2376. (left) Highly reduced (R4/5) typical ureilite; partial plane polarized and reflected light. Base width = 3 mm. (right) Same sample, cross-polarized light. Image ©; T. E. Bunch, 200

Northwest Africa 2624

Northwest Africa
Purchased 2004 August
Achondrite (ureilite)

A 241 g single, mostly crusted stone, was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): equigranular, fine-grained (<0.8 mm) typical ureilite. Olivine is highly fractured with closely spaced, subparallel fractures normal to [001]. Fractures apparently served as channel ways for reducing (smelting) activity; grain edges have a saw tooth appearance of alternating, greater reduced rims together with deposits of carbonaceous-metal-silicate-masses (CMSM) that permeated fractures and less-reduced rims that are between fractures. Olivine cores, Fa_19.6, rims are Fa_9.8-13.9; low-Ca pigeonite, Fs_16.8Wo_2.9-3.8; high silica glass in CMSM, SiO₂ = 78.8 wt. % and Al₂O₃ = 15.4 wt. %. Primary metal inclusions in olivine, Ni = 2.5 wt. % and Cr = 0.60 wt. %; reduction-derived metal, Ni = < 0.45 wt. %. Moderate level of reduction (R3); weathering is very low grade and the shock level is S2. Specimens: type example, 21.6 g, NAU; main mass, G.Hupé.

NWA 2624. (left) Sawtooth texture caused by enhanced reduction along fractures and cleavage planes in olivine and pyroxene. Only slight reduction has occurred as shown by the low abundance of blue-gray areas (R1). Small, buff-colored grains are graphite. Partial plane polarized and reflected light. (right) Same, cross-polarized light. Image ©; T. E. Bunch, 2005

Northwest Africa 2625

Northwest Africa
Purchased 2004 August
Achondrite (ureilite)

A 305 g single stone was purchased in Erfoud, Morocco. Description and classification (J. Wittke and T. Bunch, NAU): medium- to coarse-grained (<4 mm), typical ureilite with pronounced preferred orientation of silicates, which are mostly elongated with curvilinear morphology. Pigeonite shows well-defined twinning; graphite and carbonaceous-metal-silicate-masses tend to cross trend the lineation direction with some small masses poikilitically enclosed by large pigeonite. The degree of olivine-pigeonite reduction is low to moderate (R2-3). Olivine cores, Fa_20.3 (Cr₂O₃ = 0.72 wt. %), rims are Fa_8-10.8(Cr₂O₃ = 0.53 wt.%); pigeonite, Fs_17.4Wo_7.6(Cr₂O₃ up to 1.56 wt. %). Weathering is low grade and the shock level is S2. Specimens: type specimen, 22.2 g, NAU; main mass, G. Hupé.

NWA 2625. (left) Plane polarized light photomicrograph of typical ureilite that shows elongate olivine and pigeonite with preferred orientation, similar to Dho 979. Graphite distribution cross-trends foliation plane; R1; base width = 4 mm. (right) Same. Cross-polarized light. Image © T. E. Bunch, 2005

Northwest Africa 2634

Northwest Africa
Purchased 2004
Achondrite (ureilite)

A 600.2 g complete stone with fusion crust was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): mosaicized-type ureilite; elongated olivine and pigeonite in preferred orientation; highly shocked (S5) with pyroxenes completely converted to mosaic texture, olivine less so; reduction level is R3. Olivine cores, Fa_21.4, rims reduced to Fa_3.8; pigeonite, Fs_18.8Wo_9.9; sub-calcic augite, Fs₁₇Wo_16.6; vein metal, 0.3-3.7 wt. % Ni. Low weathering grade. Specimens: type specimen, 46 g, NAU; main mass, Farmer.

NWA 2634. (left) Plane light photomicrograph of a highly shocked ureilite, gray-brown grains are recrystallized pigeonite pyroxene, olivine contains planar shock features. Shock level = S3-5; R2. Base width = 5 mm. (right) Same general area, cross-polarized light. Image © T. E. Bunch, 2005

Northwest Africa 2651

Northwest Africa
Found 2003
Achondrite (ureilite)

History: An 89 g partial stone was purchased in Erfoud, Morocco in May 2004. Petrography: (J. Wittke and T. Bunch, NAU): bi-modal ureilite that contains scarce, large pigeonite grains (up to 8 mm in diameter) heterogeneously distributed throughout an equigranular, fine-grained (< 0.9 mm) matrix of olivine and compositionally similar low-Ca pyroxene. Olivine is highly fractured with closely spaced, subparallel fractures normal to [001]. Fractures apparently served as channel ways for reducing (smelting) activity; grain edges have a saw tooth appearance of alternating, greater reduced rims together with deposits of carbonaceous-metal-silicate-masses that permeated fractures and less-reduced rims that are between fractures, similar to NWA 2624. Geochemistry: Olivine cores, Fa_18.6, rims are Fa_10.7-14.3; small pigeonite, Fs_16.8Wo_2.9-3.8; large pigeonite, Fs_15.1Wo_3.3; reduction-derived metal, Ni = < 0.63 wt. %. Weathering is very low grade and the shock level is S2. Classification: achondrite (ureilite) possibly paired with NWA 2624. Type specimens: A total of 22.6 g and one thin section are on deposit at NAU. Mr. Blaine Reed is the main mass holder.

NWA 2651. Partial cross-polarized photomicrograph that shows saw-toothed edges of olivine and pigeonite decorated with dark, interstitial carbonaceous material and reduced metal. Width = 7.2 mm. Image ©; T. E. Bunch, 2005

Northwest Africa 2703

Morocco
Find 2004
Achondrite (ureilite)

History: A complete partially crusted stone weighing 121 g was purchased in Erfoud, Morocco. Petrography (J. Wittke and T. Bunch, NAU): A fine-grained (≤1 mm) ureilite that has a low level of reduction. Composition: Olivine (cores, Fa_12.3, FeO/MnO = 22 g/g), pigeonite (Fs_10.6Wo_5.1, FeO/MnO = 14 g/g), clinopyroxene (Fs_6.5Wo₃₇, FeO/MnO = 13). Metal, sulfide, and graphite ribbons also present. Classification: Achondrite (ureilite); low shock; minimal weathering. Specimens: A 20.5 g type specimen is on deposit at NAU. G. Hupé holds the main mass.

Northwest Africa 2705

Morocco
Find 2004
Achondrite (ureilite)

History: A complete 70 g stone was purchased in Erfoud, Morocco. Petrography: (J. Wittke and T. Bunch, NAU) Specimen shows well-formed, basal deformation lamellae in olivine with small enclaves of slightly rotated domains. The olivines and pyroxenes contain a large amount of fine-grained graphite inclusions. Olivine margins show limited reduction. Modal analyses of silicates (vol%): Olivine = 95, pigeonite = 3, orthopyroxene = 2. Composition: Olivine (cores, Fa_22.3; FeO/MnO = 40-47 g/g), pigeonite (small grains, Fs_7.8Wo_7.7; FeO/MnO = 8 g/g), orthopyroxene (Fs_3.5Wo_2.7). Classification: Achondrite (ureilite); moderate shock, minimal weathering. Specimens: A 16.8 g type specimen is on deposit at NAU. G. Hupé holds the main mass.

NWA 2705. The big olivine grain oriented E-W has included graphite (black); this is called a poikilitic texture (relic igneous); most smaller grains are recrystallized with 120 degree grain boundary junctions, a metamorphic texture. Initially, this assemblage formed from either partial melting - with the fractionation and separation of lower temp phases (notably plagioclase and clinopyroxene - or by crystal settling (cumulate separation). All grains show a preferred orientation, together with poikilitic texture, that is strongly suggestive of cumulate formation. (photo base = 5 mm) Image ©; T. E. Bunch, 2005

NWA 2705. The textures described in the caption above next underwent metamorphism/recrystallization followed by strong shock. This large olivine grain displays beautifully developed basal deformation bands, some kinked. Image ©; T. E. Bunch, 2005

Northwest Africa 3108

Morocco
Found 2003
Achondrite (ureilite)

A 51 g single, crusted stone was purchased in Erfoud, Morocco, in 2003. Description and classification (T. Bunch and J. Wittke, NAU): typical fine-grained (<2 mm) ureilite, foliated with large amounts of carbonaceous-reduced metal interstitial masses; olivine and pigeonite have extensive reduced rims. Olivine cores, Fa_21.1, rims, Fa_2.3-5.0 (Ni = 0.74 wt. %); pigeonite cores, Fs_16.9, rims, Fs_8.2Wo_6.8. Olivine metal inclusions. Ni = 9.9 wt. %, P = 0.42 wt. %; troilite, Ni = 0.74 - 1.15 wt. %. Shock level, S2; low weathering grade. Specimens: 8.6 g, NAU; main mass, Boswell.

NWA 3108. (left) Typical ureilite texture that shows extensive reduction alteration (blue-gray). Reduction level = R3; partial plane polarized and reflected light. Base width = 3 mm. (right) Same sample (different area), crossed polarized light, base width = 5 mm. Image ©; T. E. Bunch, 2005

Northwest Africa 3109

Morocco
Found 2003
Achondrite (ureilite)

A 32 g partial stone was purchased in Erfoud, Morocco in 2003. Description and classification (J. Wittke and T. Bunch, NAU): non-foliated ureilite with thin, reduced rims in olivine and sparse, interstitial masses of carbonaceous - reduced metal; prominent interstitial clusters of ribbon-like graphite; Cr₂O₃ enrichment in silicates. Olivine: cores, Fa_23.3 with 0.63 wt. % Cr₂O₃; rims, Fa_7.6 and 0.15 wt. % Cr₂O₃. Pigeonite, Fs_17.8Wo_3.3 (Cr₂O₃ = 1.10 wt. %). Presence of (Fe,Cr)₃C in interstitial carbonaceous masses (Fe = 78.8 wt. %, Cr = 13.5 wt. %; Ni = 0.52 wt. %; Co = 0.32 wt. % and C = 6.9 wt. % by difference) and an SiO₂ phase. Shock level is S2; lightly weathered. Specimens: 6.5 g, NAU; main mass, Boswell.

NWA 3109. Typical ureilite texture, R2; plane polarized light; base width = 3 mm. (right) Same sample, crossed polarized light. Image ©; T. E. Bunch, 2005