L Chondrites


El Tigre (19°58'2" N, 103°°3'6" W)

Jalisco, Mexico
Fell December 23, 1993
Ordinary chondrite (L6)

Three stones, weighing ~5 kg, fell near the village of El Tigre. A fireball was witnessed in Puerto Vallarta and along a line in an east-southeast direction. Three stones were recovered several days later in a farmer's field. One stone (328 g) was purchased by a collector in 1994, location of other two stones is unknown. Classification and mineralogy (T. Bunch and J. Wittke, NAU): olivine, Fa24.6; plagioclase, An12. Shock stage, S2; weathering grade W0. Specimens: type specimen, 19.2 g and one thin section at NAU; remainder of this stone with anonymous collector.


Northwest Africa 2085

Morocco
Found 2003
Ordinary chondrite (L melt rock)

A 2.7 kg single stone was purchased in Rissani, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): exceptional melt rock: centimeters-size L chondrite clasts are surrounded by crystallized melt. The melt contains oblate to round, eutectic-textured, masses (up to 2.5 mm) of taenite metal set in troilite. The metal/troilite complexes show strong flow alignment in a matrix of tabular to equant olivine (< 0.8 mm), which has no apparent preferred orientation, and SiO2-rich glass, in addition to small, recrystallized chondrite fragments. Melt olivine, Fa22.8 (22.1-23.8); taenite, Ni = 15.4 wt%, range, 13.6-16.1 wt%; troilite, Ni = 0.42 wt%; glass, SiO2 = 74.6 wt%, FeO = 3.6 wt%. Clast chondrules and matrix are partially recrystallized from shock effects; olivine, Fa22.2-23.9; orthopyroxene, Fs18-19.9Wo1.4-2.0. Shock level, S4 to S6; weathering grade, W1/2. Specimens: 88.5 g, and one thin section, NAU; main mass, Farmer.

NWA-2085. Image width = 10 cm. Image © T. E. Bunch, 2007


Northwest Africa 2351

Northwest Africa
Purchased 2004 January
Ordinary L4 chondrite (melt breccia)

A 69 g complete and oriented stone was purchased in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): moderately shocked (S3) L4 host clasts enclosed by and partially intruded by recrystallized melt (grain size <0.35 mm) and cataclastic host material (grain size <0.45 mm). Large metal-sulfide inclusions (up to 4 mm) in recrystallized masses have metal interiors of Ni = 4.6 - 6.9 wt % with rims of Ni = 12.3 - 21.5 wt %. No flow fabric shown in the one plane orientation studied. Host olivine, Fa24.6-25.9 (FeO/MnO = 46.8-48.9); Fs22.3Wo2.2; recrystallized melt olivine, Fa21.2-24.6 (FeO/MnO = 38.6-49.3); Fs19.8-22.7Wo2.7-6.9. Weathering grade, W2-3. Specimens: 14.2 g, NAU; main mass, Drummond.


Northwest Africa 2979

Algeria
Purchased 2005
L chondrite (L chondrite microporphyry)

History: A completely crusted and very fresh 23.2 g stone was purchased in Erfoud, November 2005.
Petrography (T. Bunch and J. Wittke, NAU): small (<0.5 mm) euhedral to subhedral olivine crystals are set in a mesostasis of dark glass, skeletal augite, and tiny (<0.03 mm) spheres of Ni-Fe metal and sulfides. Sub-millimeter clusters of fine-grained, subhedral olivine with scare mesostasis are scattered throughout.
Mineralogy: mean composition of unzoned olivine, Fa26.8±13.7, FeO/MnO = 36-54 g/g, Cr2O3 in olivine = 0.35-0.78 wt%; augite, Fs39.4Wo25.8; quartzo-feldspathic glass contains 4.6 wt% FeO, 1.75 wt% MgO, and 0.39 wt% Cr2O3; chromite, Cr/(Cr+Al) = 0.83; kamacite, Ni = 5.3 wt%; taenite, Ni = 20.1 wt%.
Oxygen isotopes: Replicate analyses by laser fluorination technique (D. Rumble, CIW) are δ17O, 3.61 and 3.64; δ18O, 4.66 and 4.69 and Δ17O, 1.164 and 1.178, respectively and are consistent with L chondrites.
Classification: L chondrite microporphyry. NWA 2979, and NWA 2981, another microporphyric chondritic, are very similar to chondritic microporphyric melt clasts common in ordinary chondritic breccias that are assumed to be products of quenched impact melts (Dodd and Jarosewich, 1975; Rubin 1985). Apparently, NWA 2979 was ejected from its parent body during an impact event.
Specimens: type specimen, 4.8 g, NAU; main mass holder, Farmer/Strope.

NWA 2979. Photomicrograph in plane light; note fine-grained clots at upper middle and right; width of photograph is 3.5 mm. © T. E. Bunch, 2006.

NWA 2979. Electron backscattered image of microporphyry showing extensive quenching of mesostasis. Note clot of troilite with included metal (light gray and white) and skeletal chromite (medium gray); olivine microphenocrysts are strongly zoned (in contrast with NWA-2981) ; largest olivine grain is approximately 200 µm. Image © J. H. Wittke, 2006.

Comparison of Microporphyries. Blue lines point to fine-grain clots within the microporphyries. Image © J. H. Wittke & T. E. Bunch, 2006.

Reference

Dodd, R. T. and E. Jarosewich (1975) Meteoritics 11, 1-19. Rubin, A. E. (1985). Rev. Geophys. 23, 277-300.


Northwest Africa 2981

Algeria
Purchased August 2005
L chondrite (L chondrite microporphyry)

NWA 2981. Width of sample is about 2 cm. Image © T. E. Bunch, 2006.

History: A small 19 g, lightly weathered and partially crusted stone was purchased in Erfoud, August 2005.
Petrography (J. Wittke and T. Bunch, NAU): consists of mostly small (<0.5 mm) euhedral to subhedral olivine crystals set in a dark, MgO-, FeO-bearing feldspathic glass together with clusters of fine-grained (<0.1 mm) anhedral olivine with scarce glass are scattered throughout as well as millimeter-sized clumps of Ni-Fe metal cores with sulfide rims. Mesostasis glass contains a connected network of skeletal, quench-formed augite and tiny, round to irregular shaped metal and sulfide grains.
Mineralogy: Mean composition of olivine is Fa22.6, FeO/MnO = 46 g/g; rare orthopyroxene is Fs19.1±7.1; mesostasis diopside, Fs12Wo43.4; pigeonite, Fs17.4-28.6Wo12-5.8 kamacite, Ni = 6.8 wt%; mesostasis glass = SiO2, 67 wt%; Al2O3, 10.2 wt%; CaO, 5.7 wt%; Na2O, 2.17 wt%; K2O, 2.13 wt%; MgO, 5.9 wt% and FeO, 3.0 wt%.
Classification: Ordinary chondrite (impact melt rock with L composition).
Specimens: A 4.1 g sample is on deposit at NAU; G. Hupe holds the main mass.

NWA 2981. Photomicrograph in plane-polarized light; width of photograph is 9 mm. Image © T. E. Bunch, 2009.

NWA 2981. Photomicrograph in cross-polarized light; note fine-grained clot at upper right; isotropic mesostasis glass appears black; width of photograph is 3.5 mm. Image © T. E. Bunch, 2006.

NWA 2981. Electron backscattered image of microporphyry; olivine microphenocrysts are not significantly zoned; note quenched olivine and pyroxene crystals in mesostasis glass. Image © J. H. Wittke, 2006.

NWA 2981. Electron backscattered image of quenched olivine and pyroxene crystals in mesostasis glass. Image © J. H. Wittke, 2006.


Northwest Africa 2986

Algeria
Find 2005
L chondrite (L melt)

History: A 71 g stone was found in Southern Algeria in 2005 and sold in Erfoud in November 2005.
Physical characteristics: A partial stone with no residual crust is reddish-brown in color with raised, small (< 1 mm) bumps of lightly oxidized metal and sulfide.
Petrography (T. Bunch and J. Wittke, NAU): very dark interior that is mostly shock-melted with three distinct grain sizes: (1) shocked and unmelted olivine and orthopyroxene fragments (< 0.3 mm), (2) melt-crystallized olivine > orthopyroxene > plagioclase > augite (< 0.05 mm) and (3) very fine - grained matrix (< 0.01 mm) that consists of olivine, orthopyroxene, SiO2-rich feldspathic glass, and tiny metal melt spheres. Large oblate to rounded melt-formed taenite is commonly mantled by sulfide and is < 3 mm in size. No metal-sulfide eutectic structures were noted. There is a strong directional flow orientation of the metal-sulfide complexes.
Geochemistry: Olivine megacrysts are Fa23.6, FeO/MnO = 50 g/g, mid-size olivine is Fa20.2-27.6, FeO/MnO = 44-54 g/g. Orthopyroxene megacrysts are Fs19.6Wo2.6, FeO/MnO = 33 g/g, and augite is Fs15.6Wo30.4. Taenite Ni content is 15.2 wt % and chromite fragments are Cr/(Cr+Al) = 0.84.
Classification: ordinary chondrite (L melt). Sample is similar to NWA 2085, but lacks metal-sulfide eutectic structures. The shock level is S3-5 and the weathering effects are moderate (no residual kamacite and taenite is partially oxidized).
Type specimens: A total of 14.6 g and one thin section are on deposit at NAU. Mr. Edwin Thompson is holder of the main mass.


Northwest Africa 3334

Algeria
Find: 2004
Ordinary chondrite (L melt rock)

History and physical characteristics: A 41.5g complete stone with no fusion crust was found in Algeria in 2003 and sold in Rissani, Morocco in 2004. The stone is dark brown in color with raised, small bumps of highly oxidized metal and sulfide.
Petrography: (T. Bunch and J. Wittke, NAU) Very dark interior that is mostly shock-melted with three distinct grain sizes: 1) shocked (S3-4), unmelted olivine and orthopyroxene fragments (<0.4 mm), 2) melt-crystallized olivine > orthopyroxene > plagioclase > augite (<0.05 mm), and 3) very fine-grained matrix (<0.01 mm) that consists of olivine, orthopyroxene, and SiO2-rich feldspathic glass. Variable sized (< 2.5 mm) oblate to sub-rounded melt-formed, oxidized metal with oxidized FeS inclusions are randomly dispersed throughout. There is no noticeable flow orientation of these original metal-sulfide complexes.
Mineral compositions and geochemistry: Olivine megacrysts (Fa24.3; FeO/MnO = 52 g/g), midsized olivine (Fa22.2-26.6; FeO/MnO = 48-58 g/g). Orthopyroxene megacrysts are Fs20.5Wo2.3; FeO/MnO = 29 g/g, augite (Fs13.8Wo31.0), and chromite fragments, Cr/(Al+Cr) = 0.83).
Classification: Ordinary chondrite (L melt rock, shock level is S5 and it is heavily weathered. This sample is similar to NWA 2085, but is much less weathered and to NWA 4286, which has strong fabric orientation and is less weathered.
Type specimen: A total of 8.2 g and one thin section are on deposit at PSF and one thin section at NAU. PSF is also the main mass holder.


Northwest Africa 4286

Algeria
Find: 2005
Ordinary chondrite (L melt rock)

History: A stone was found in southern Algeria in 2005 and sold in Erfoud in November 2005.
Physical characteristics: A 71 g partial stone with no residual crust is reddish brown in color with raised, small (<1 mm) bumps of lightly oxidized metal and sulfide.
Petrography: (T. Bunch and J. Wittke, NAU) Very dark interior that is mostly shock-melted with three distinct grain sizes: 1) shocked and unmelted olivine and orthopyroxene fragments (<0.3 mm), 2) melt-crystallized olivine > orthopyroxene > plagioclase > augite (<0.05 mm), and 3) very fine grained matrix (<0.01 mm) that consists of olivine, orthopyroxene, SiO2-rich feldspathic glass, and tiny metal melt spheres. Large oblate to rounded melt-formed taenite is commonly mantled by sulfide and is <3 mm in size. No metal-sulfide eutectic structures were noted. There is a strong directional flow orientation of the metal-sulfide complexes. No residual kamacite and taenite is partially oxidized.
Mineral compositions and geochemistry: Olivine megacrysts (Fa23.6; FeO/MnO = 50), midsize olivine (Fa20.227.6; FeO/MnO = 4454). Orthopyroxene megacrysts (Fs19.6Wo2.6; FeO/MnO = 33), augite (Fs15.6Wo30.4). Taenite (Ni = 15.2 wt%) and chromite fragments (Cr/[Cr+Al] = 0.84).
Classification: Ordinary chondrite (L melt rock); S5, moderate weathering. This sample is similar to NWA 2085, but lacks metal-sulfide eutectic structures.
Type specimen: A total of 14.6 g and one thin section are on deposit at NAU. Thompson is holder of the main mass.


Photographs of L Chondrites

NWA 1941. Image © T. E. Bunch, 2004

NWA 1947. Image © T. E. Bunch, 2003

NWA 2785. Pictures of sawn surface. Note extreme variation in chondrule size (both images at same magnification). Base width = 5 mm. Image © T. E. Bunch, 2005

NWA 2785. Thin section in PPL. Image © T. E. Bunch, 2005