Acapulcoites


Summary of Acapulcoite Charactersitics

Minerals and compositions:

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

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


Northwest Africa 2627

Northwest Africa
Found 2004
Achondrite (acapulcoite)

A 68 g mostly crusted, partial stone was purchased in Erfoud in October 2004. Description and classification (T. Bunch and J. Wittke, NAU): recrystallized into polygonal and subhedral grains with the exception of large orthopyroxene grains (up to 3 mm) that poikilitically enclose olivine; heavily fractured, variable grain size, and heterogeneous distribution of phases. Modal analyses (vol. %): orthopyroxene, 44; olivine, 41; FeS, 6; metal (and Fe-oxides), 5; plagioclase, 3 and minor merrillite, Ca-pyroxene and chromite. All silicates have very homogeneous compositions; olivine, Fa13.1 (FeO/MnO = 26); orthopyroxene, Fs12.2Wo2.7 (FeO/MnO = 13.9); plagioclase, An21.9; metal, Ni = 6.7 wt. % Ni. Oxygen isotope analyses are consistent with winonaites, mineralogy and mineral compositions are more consistent with lodranite assemblages. Weathering grade is W2/3 with ferric Fe staining; shock level is S2. Specimens: type example, 13.7 g, NAU: main mass, Strope/Farmer.

Northwest Africa 2656

Morocco or Algeria
Found 2003
Achondrite (acapulcoite)

History: A 386 g broken stone with weathered fusion crust (part of a larger ~7.5 kg mass found in 2003) was purchased in Erfoud, Morocco, in 2004 for N. Oakes.
Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS) The specimen is recrystallized into homogeneous polygonal and subhedral grains with a grain size of <1 mm and an approximately equal distribution of phases.
Composition: Olivine (Fa8.0; FeO/MnO = 16-19 [n=25]), orthopyroxene (Fs8.4Wo2.4; [n=17]), plagioclase (An18.3-21.0Or2.8-3.4), chromite ((Cr/Cr+Al) = 0.85; Mg/(Mg+Fe) = 0.41). Troilite, schreibersite, and kamacite are also present.
Oxygen isotopes: (D. Rumble, CIW) Replicate analyses by laser fluorination gave δ17O = 1.71, 1.69; δ18O = 5.05, 5.04; Δ17O = -0.953, -0.973 (all ‰).
Classification: Achondrite (acapulcoite); low shock, moderate weathering.
Specimens: A 21 g type specimen and one polished thin section are on deposit at NAU. Oakes holds the main mass.

Reference

Rumble, D., III, Irving, A. J., Bunch, T. E., Wittke, J. H. and Kuehner, S. M. (2005), Discrimination of acapulcoites and lodranites from winonaites. Abstr. 68th Met. Soc. Mtg., #5138.


Northwest Africa 2775

Algeria
Find: 2005
Achondrite (acapulcoite)

History and physical characteristics: A dark brown, 222 g, partially crusted stone was purchased in Erfoud, Morocco, in November 2005.
Petrography: (J. Wittke and T. Bunch, NAU; A. Irving, UWS) Recrystallized homogeneous, polygonal to subhedral grains <0.8 mm in size.
Mineral compositions and geochemistry: Olivine (Fa14.5±0.2; FeO/MnO = 30.5, MnO > 0.02 wt. %), orthopyroxene (Fs13.3±0.2Wo3.0; FeO/MnO = 17), diopside (Fs6.8Wo41.9; FeO/MnO = 12), plagioclase (An17.4), Fe,Ni rich metal (Ni = 22.5 wt. %). FeS is also observed.
Oxygen isotopes: (D. Rumble, CIW) Multiple analyses of different samples of the rock by laser fluorination are δ17O = +0.78 and +0.97, δ18O = +2.94 and +3.25, Δ17O = -0.764 and -0.743 (all ‰).
Classification: Achondrite (acapulcoite).
Type specimen: A 20.1 g sample is on deposit at NAU. Turecki and Reed hold the main mass.

NWA 2775. Width of image is 17 mm. © T. E. Bunch, 2008

NWA 2775. Backscattered electron image Black = plagioclase, grays = olivine and pyroxene, white = metal. © J.H. Wittke, 2008


Northwest Africa 4816

Northwest Africa
Find: 2006
Achondrite (acapulcoite)

History and physical characteristics: A 63g stone was purchased in Erfoud, Morocco in 2006 by Stefan Ralew. The partial stone has moderate surface weathering of broken areas. Small metal spherules and droplets protrude through a thin, residual fusion crust.
Petrography (T. Bunch and J. Wittke, NAU): Highly enriched in kamacite metal, mineral modes (in vol. %) are: orthopyroxene, 33; olivine, 25; kamacite, 24; diopside, 15; plagioclase and felsic glass, 3; and FeS + chromite, 1.0. Silicates are fine-grained (mean = 0.60 mm) and show euhedral to subhedral grain outlines. Orthopyroxene contains microns-sized glass blebs. Rare, round to ovoid granular clusters may represent relict chondrules. Shock level is S2 and the weathering grade is W1.
Mineral compositions: Olivine, Fa5.6; FeO/MnO = 12. Orthopyroxene is Fs6.2Wo2.1, FeO/MnO = 9, and diopside is Fs2.8Wo45.5, FeO/MnO = 7. Plagioclase is An66, chromite Cr/(Cr+Al) = 0.69, and kamacite contains 6.1 wt. % Ni. Felsic glass is (in wt. %): SiO2, 51.2; Al2O3, 20.3; CaO, 10.8; Na2O, 2.6; K2O, 0.8; MgO, 12.0 and FeO. 3.1.
Classification: Achondrite (acapulcoite).
Type specimen: A 12.4 g sample is on deposit at NAU. Mr. Stefan Ralew holds the main mass.

NWA 4816. Backscattered electron image Black = plagioclase, grays = olivine and pyroxene, white = metal. © J.H. Wittke, 2008


Northwest Africa 5782

Morocco
Purchased: September 2008
Achondrite (acapulcoite/lodranite)

History and physical characteristics: Purchased by Blaine Reed at the Denver Mineral Show. Two pieces with a total mass of 130 g were found in a batch of meteorites. The stones experienced moderate terrestrial weathering, but some fusion crust is still visible.
Petrography (T. Bunch and J. Wittke, NAU; A. Irving, UWS; P. Sipiera, PSF): A polymict breccia of subrounded to subangular clasts (exhibiting some preferred orientation) set in a cataclastic matrix with minor glass and secondary Fe hydroxide veinlets. The most abundant clasts (45 vol%) are recrystallized acapulcoites with polygonal texture (mean grain size is 0.225 mm). Coarser grained, protogranular to polygonal textured clasts (25 vol%) are various types of lodranites (mean grain size is 0.745). The matrix (30 vol%) contains debris from both types of lithology, and additionally rare, small xenolithic fragments of augite with exsolution lamellae of Ca-poor pyroxene.
Mineral compositions and geochemistry: Acapulcoites Olivine Fa8.7-13.3 (FeO/MnO = 1727); low-Ca pyroxene Fs9.0-4.1Wo2.1-3.0; clinopyroxene Fs4.8-7.5Wo45.7-47.9. Lodranites Olivine Fa8.6-13.7 (FeO/MnO = 1618); low-Ca pyroxene Fs12.713.7Wo2.8; clinopyroxene Fs4.6Wo46.7 (Al2O3 1.10 wt%, Cr2O3 1.83 wt%, TiO2 0.63 wt%). Xenolithic fragment clinopyroxene Fs19.5Wo42.8 (FeO/MnO = 24); orthopyroxene Fs40.7Wo4.1 (FeO/MnO = 32). Oxygen isotopes (D. Rumble, CIW): acid-washed material analyzed in duplicate by laser fluorination gave, respectively δ17O = 0.53, 0.66; δ18O = 3.24, 3.03; Δ17O = -1.172, -0.936 (all ‰).
Classification: Achondrite (acapulcoite, anomalous). This specimen is unusual among acapulcoites in that it is a breccia and contains a significant component of lodranite clasts.
Type specimens: A total of 20.8 g of material and one polished thin section are on deposit at FMNH in the PSF collection; another thin section is on deposit at NAU. The main mass is held by B. Reed.


Northwest Africa 6557

Morocco
Find: 2009
Achondrite (Acapulcoite)

History: A very fresh 68 g stone with fusion crust was purchased by Darryl Pitt from a dealer in Erfoud, Morocco.
Petrography (T. Bunch and J. Wittke, NAU): Equigranular recyrtstallized texture with triple junctions. Mean grain size is 0.24 mm. Mineral modes (vol%): orthopyroxene, 38; olivine, 35; plagioclase, 12. Ca-pyroxene, 7; opaques, 8. Shock level and weathering grade are low.
Geochemistry: Orthopyroxene, Fs12.5 (FeO/MnO = 12); olivine, Fa13.9 (FeO/MnO= 16); plagioclase, An6.8Or5.5; chromite, cr# = 87; Ca-pyroxene, Fs8.1Wo36.8; kamacite (Ni = 6.2 wt%). Oxygen isotopes (D. Rumble, CIW): replicate analyses of acid-washed material by laser fluorination gave, respectively δ17O = 0.64, 0.55; δ18O = 3.05, 2.79; Δ17O = -0.962, -0.913 (all ‰).
Classification: Achondrite ( Acapulcoite).
Specimens: A total of 14 g is on deposit at NAU. Mr. D. Pitt holds the main mass.


Other Acapulcoites

IDLocationDateMass (g)StateOlivinePyroxenesFeldsparComments
NWA 2699Erfoud, Morocco20051294S1, W3Fa8.2±0.2Fs9.1±0.2Wo3.0An23.8paired with NWA 2656
photograph below)
NWA 2714Erfoud, Morocco2005100S1, W3/4Fa8.1-An22.2chromite, Cr/(Cr+Al) = 0.85;
paired with NWA 2656
(photograph below)
NWA 2866Erfoud, Morocco2005213S1, W3Fa8.2±0.2 opx Fs9.3±0.2;
cpx Fs4.2Wo43.5
An24.5Or2.8chromite, Cr/(Cr+Al) = 0.70;
paired with NWA 2656
(photograph below)


Photographs of Acapulcoites

NWA 2699. Photomicrograph in partially cross polarized light; width of photograph is 13 mm. Image © T. E. Bunch, 2007.

NWA 2714. Photomicrograph in partially cross polarized light; width of photograph is 13 mm. Image © T. E. Bunch, 2007.

NWA 2866. Photomicrograph in partially cross polarized light; width of photograph is 13 mm. Image © T. E. Bunch, 2007.