Lodranites


Summary of Lodranite Charactersitics

Minerals and compositions:

Mineral modes (vol. %): orthopyroxene > olivine > Ca-pyroxene > plagioclase ≥ FeS

Texture: Polygonal, metamorphic (120° triple junctions); mean grain size: >0.5 mm for lodranites (Note that samples with grain size <0.4 mm are acapulcoites).


Northwest Africa 4448

Algeria
Found 2005
Achondrite (lodranite)

History: A partial stone was recovered from the lower Algerian desert in 2005 and sold in Erfoud, Morocco in 2006
Physical characteristics: A partially crusted, 36.3 g stone with a freshly fractured surface.
Petrography (T. Bunch and J. Wittke, NAU): granoblastic texture with a grain size of 0.05 to 1.7 mm, mean = 0.55 mm. The largest grains are orthopyroxene oikocrysts that enclose rounded olivine chadacrysts. Modal analyses (in vol%): orthopyroxene, 49 (oikocrysts = 4); olivine, 42; metal, 6; sulfide, chromite, and phosphates, 3. Weathering grade and the shock level are low.
Geochemistry: Orthopyroxene, Fs11.2Wo2.2, FeO/MnO = 16 to 18; orthopyroxene oikocrysts, Fs10.6Wo1.6; olivine, Fa8.5, FeO/MnO = 19 to 23; sulfide Ni = 2.36 wt%; metal Ni = 5.4 wt%; chromite cr# = 80; merrilite CaO = 47.5 wt% and P2O5 = 46.3 wt%; apatite CaO = 56.9 wt% and P2O5 = 42.4 wt%; Oxygen isotopes (D. Rumble, CIW): A cleaned and metal-free sample was analyzed by laser fluorination. Replicate analyses are, respectively, δ17O, -0.539 and -0.442; δ18O, 3.551 and 3.413; Δ17O, -1.3291 and -1.3534.
Classification: Achondrite (lodranite).
Type specimens: 6.3 g and one thin section are on deposit at NAU. The main mass is held by Mr. N. Oakes.

NWA 4448. Base width = 7 mm. Image © T. E. Bunch, 2008.


Northwest Africa 4663

Algeria
Find: 2006
Achondrite (lodranite)

History and physical characteristics: A 564 dark stone with desert varnish and little remaining fusion crust was found in Western Sahara in 2006 and purchased by A. Aaronson in October 2006.
Petrography: (T. Bunch and J. Wittke, NAU) Protogranular texture with a grain size (metal excluded) of 0.2 to 1.65 mm, the mean is 0.9 mm. Metal grains are as large as 2.2 mm, the mean is 1.25 mm. Oikocrysts of orthopyroxene enclose olivine, a poikilitic texture, and Ca-pyroxene contains very thin (< 0.002 mm) orthopyroxene exsolution lamellae. Irregular patches of vermicular FeS (< 0.01 mm) occur mostly within orthopyroxene. Mineral modes (vol. %) are: orthopyroxene = 36, olivine = 30, metal and oxidized metal = 17, troilite = 8, diopside = 8, and plagioclase = 1.
Mineral compositions and geochemistry: Orthopyroxene (Fs10.0-10.3Wo2.2-2.8; FeO/MnO = 13 g/g), olivine (Fa5.4-6.1; FeO/MnO = 17 g/g), diopside (Fs4.3Wo45.9), metal (4.7-10.3 wt % Ni) and plagioclase (An20Or2.7).
Oxygen isotopes: (D. Rumble, CIW) A cleaned and metal-free sample was analyzed by laser fluorination. Replicate analyses are respectively, δ17O = -1.025 and -0917; δ18O = 1.15 and 1.20; Δ17O = 4.13 and 4.01.
Classification: Achondrite (lodranite); low to moderate weathering (metal within 4 mm of the surface tends to be oxidized) and low shock level.
Type specimen: A 23 g sample is on deposit at NAU. A. Aaronson holds the main mass.

NWA 4663. Protogranular texture (base width = 7 mm). Image © T. E. Bunch, 2007.


Northwest Africa 4833

Morocco
Find: 2007
Achondrite (lodranite)

History and physical characteristics: A 608 g dark stone with a dull desert varnish and no remaining fusion crust was found in the Western Sahara region of Morocco in 2007 and purchased by A. Aaronson in July 2007.
Petrography: (T. Bunch and J. Wittke, NAU): This harzburgite - equivalent stone displays a coarse-grained (olivine grains up to 6 mm) hypidiomorphic texture. Orthopyroxene shows a common lobate grain boundary relationship with olivine. Orthopyroxene is highly decorated with exsolved linear to bleb-shaped diopside (0.002 to 0.04 mm in size) that is oriented parallel to at least three crystal planes of the orthopyroxene host. Olivine is decorated with 0.005-0.02 mm sized ovoid-shaped microlites of plumose chromite set in anhedral diopside. Mineral modes (vol. %) are: olivine = 65, orthopyroxene = 30, metal and oxidized metal = 2, FeS, Cr = 2.3 wt %; chromite and diopside = 3, no plagioclase was found. The shock level is S3 with moderate mosaic extinction in olivine and orthopyroxene and minor shock twinning in both.
Mineral compositions: Olivine (Fa10.1; FeO/MnO = 23), orthopyroxene (Fs9.4Wo2.3; FeO/MnO =14), diopside (Fs8.0Wo45.9; FeO/MnO = 11), metal (2.98 wt. % Ni) and FeS (Cr = 1.1 wt. %). Chromite Cr/(Cr+Al) = 0.85.
Classification: Achondrite (lodranite).
Type specimen: A 22.2 g sample is on deposit at NAU. Mr. A. Aaronson holds the main mass.

NWA 4833. Base width = 17 mm. Image © T. E. Bunch, 2008.


Northwest Africa 4875

Northwest Africa
Find: 2007
Achondrite (lodranite)

History and physical characteristics: A 904g dark brown stone was purchased by A. Aaronson in Morocco in July 2007. The irregular-shaped stone has no remnant fusion crust and has been desert-polished by eolian processes.
Petrography (T. Bunch and J. Wittke, NAU): This coarse-grained harzburgite-like specimen is brecciated and contains olivine and orthopyroxene grains of ~ equal size (up to 5 mm in dia.). In addition, intact lithologic clasts contain minor interstitial clinopyroxene, kamacite, troilite, and pentlandite, no plagioclase was found. Olivine shows small (< 0.02 mm), randomly oriented irregular- to ovoid-shaped inclusions of chromite and diopside. Some of these inclusions exhibit a symplectitic relationship with host olivine. Orthopyroxene has twin lamellae and tiny metal and sulfide inclusions oriented parallel to the (100) crystallographic plane. Oxidation of kamacite is extensive and imparts a dark stain throughout the sample. Shock level is S3.
Mineral compositions: Olivine is Fa10.3 and FeO/MnO = 24; orthopyroxene is Fs9.6Wo1.4 and FeO/MnO = 14; clinopyroxene is Fs3.6Wo45.7 and contains 1.35 wt. % Cr2O3. Chromite Cr/(Cr+Al) = 0.84 and troilite contains 2.5 to 5.4 wt. % Ni.
Classification: Achondrite (lodranite), possibly paired with NWA 4478, but not with NWA 4833.
Type specimen: A total of 21.2 g is on deposit at NAU. Mr. A. Aaronson holds the main mass.

NWA 4875. Image width = 17 mm. © T.E. Bunch, 2008


Northwest Africa 5210

Northwest Africa
Find: 2007
Achondrite (Lodranite)

History and physical characteristics: A 28.8 g stone was purchased from a dealer in Erfoud Morocco in 2007.  The dark remnant fusion crust is highly polished from wind ablation and is lightly iron stained.
Petrography (T. Bunch and J. Wittke, NAU): Protogranular texture with a mean grain size of 0.82 mm. Rare orthopyroxene oikocrysts contain small round olivine grains. Micron size inclusions of FeS + metal + SiO2 are aligned along annealed fractures in olivine. Mineral modes (in vol. %) are: orthopyroxene 42, olivine 40, metal and sulfide 10, Ca-pyroxene 5, plagioclase 3. Weathering and shock effects are minimal.
Mineral compositions: Orthopyroxene, Fs14.6Wo2.7 (FeO/MnO = 19); olivine, Fa13.4 (FeO/MnO = 24),Ca-pyroxene, Fs8.2Wo47.3 (Cr2O3 1.53 wt. %); plagioclase, An26.3Or2.7; metal Ni = 7.1 wt. %.
Classification: Achondrite (lodranite).
Type specimen: A total of 5.8 g are on deposit at NAU. Dr. David Gregory is the main mass holder.

NWA 5210. Base width = 9 mm. Image © T. E. Bunch, 2008.

NWA 5210. Image taken with a combination of transmitted and reflected light; bright white areas are metal. Base width = 7 mm. Image © T. E. Bunch, 2009.