Diogenites


Diogenites are the D class of the HED achondrite clan (howardite-eucrite-diogenite). They are composed essentially of orthopyroxene and hypersthene, with minor amounts of plagioclase, olivine, troilite, and chromite. Like eucrites, diogenites contain little NiFe metal. Although most diogenites have been crushed to various degrees, some remaining hypersthene crystal fragments are as large as 5 cm (~2 inches). Even then, component fragments show rotation and small pockets of pulverized material.

Sawn surface of the Johnstown diogenite that shows fragmented orthopyroxene clasts and crushed matrix. Base of specimen is 15.4 cm (6 in). Source: http://www.meteoritetimes.com/Back_Links/2002/april/Meteorite_of_Month.htm.

Unlike eucrites that formed from volcanic surface flows, diogenites probably formed by crystal separation from the parent magma. Eucrites and diogenites came from the same parent body, eucrites from the surface or near surface and diogenites from deeper within. Recently, several diogenites have been recovered that contain up to 30 vol% of olivine and are classified as olivine diogenites. These meteorites may be samples of parent body rocks that are deeper than pyroxene diogenites. Little by little, we are receiving rock samples of Vesta that are from deeper and deeper depths. Eventually, we may receive Vesta meteorites that are mostly olivine and would represent the earliest differentiates.

Summary of Diogenite Characteristics

Minerals and compositions:

Texture: Igneous, protogranular, poikilitic; some are cataclastic. recrystallized-granular; grain size: millimeters to centimeters.

Diogenites can be subdivided into subgroups based on terrestrial ulramafic rock terminology and modal amounts of opx + plag + olv (see diagram below).

Classification diagram (based on Le Maitre et al. 2002; figure and data from Bunch et al. 2010, MAPS 45) showing modal compositions of plagioclase and olivine-bearing diogenites. The names are modified from Bunch et al., who used the prefix "HED," to better agree with those of Beck and McSween (2010).

A slightly different scheme is presented by Beck and McSween (2010, MAPS 45, 850-872). All ultramafic samples with opx + olv ≥ 90 vol% are considered diogenites. Those with ≥90 vol% opx are classified as orthopyroxenitic diogenites; those with ≥90 vol% olv are dunitic diogenites; the remainder are harzburgitic diogenites. The only differences between the two schemes are that Beck and McSween combine the olivine orthopyroxenitic diogenite and harzburgitic diogenite classifications of Bunch et al. into a single classification (harzburgitic diogenite) and have no noritic diogenite classification..

Diogenite Poster PDF (large file) - presented at MetSoc 2007


Arabian Peninsula 001

United Arab Emirates
Find: 2006
Achondrite (diogenite)

History and physical characteristics: This 145 g stone, together with five other achondrites (AP 002, 003 004, 005, 006) and 18 ordinary chondrites, were found near the Rub al-Khali desert (Empty Quarter) by native workers in 2005-6. These stones were sent to an American collector for verification in August 2006. AP 001 is a very fresh stone with black crust and retains flow ridges.
Petrography: (T. Bunch and J. Wittke, NAU) Unbrecciated medium-grained orthopyroxenite with inclusions of euhedral to subrounded chomite. Contains (vol%): orthopyroxene, 94; chromite, 4; FeS 2 and a trace of olivine. Orthopyroxene exhibits heavy undulatory extinction, shear zones show intense granulation and distortion of minerals.
Mineral compositions and geochemistry: Orthopyroxene (Fs21.6Wo2.0; FeO/MnO = 29); olivine (Fa27.3, FeO/MnO = 45) chromite, Cr/(Cr+Al) = 0.79.
Classification: Achondrite (diogenite). Moderately shocked and slightly weathered.
Type specimen: A 21 g sample is on deposit at NAU. The main mass holder is anonymous.

AP 001. Unbrecciated diogenite that shows orthopyroxenes and chromite grains that are partially fragmented and deformed. Base width = 9 mm, crossed polarizers. Image © T. E. Bunch, 2007.


Arabian Peninsula 003

United Arab Emirates
Find: 2006
Achondrite (diogenite)

Physical characteristics: A 56 g stone that has been heavily sandblasted, no crust remains.
Petrography: (J. Wittke and T. Bunch, NAU) Unbrecciated with well-developed preferred orientation of orthopyroxene. Large chromite crystals (<2 mm) are surrounded by a corona-like "necklace" of very small orthopyroxene and olivine grains. Chromite also has very tiny (<0.01 mm) inclusions of pigeonite, diopside, plagioclase, and FeS. Small grains of FeS, metal, and clusters of olivine occur as inclusions in cumulate orthopyroxene.
Mineral compositions and geochemistry: cumulate orthopyroxene (Fs23.5Wo2.3; FeO/MnO = 28); orthopyroxene inclusions (Fs21Wo2.7; FeO/MnO = 28), olivine (Fs25.5; FeO/MnO = 43); diopside inclusions (Fs11.1Wo42); chromite, Cr/(Cr+Al) = 0.76.
Classification: Achondrite (diogenite). Internal weathering is very low as is the shock level.
Type specimen: An 11.2 g sample is on deposit at NAU. The main mass holder is anonymous.

AP 003. Linear orientation of orthopyroxene with irregular grain boundaries (lobate and sutured). Texture consistent with filter pressing compression and minor metamorphism. Base width = 14 mm; crossed polarizers. Note precipitation or corona-like "necklace" around chromite. In addition, there are apparent relict islands of a primary opx whose bulk was assimilated by a later generation of large opx. Base width = 6 mm. Crossed polarizers. Image © T. E. Bunch, 2007.


Arabian Peninsula 004

United Arab Emirates
Find: 2006
Achondrite (diogenite)

Physical characteristics: A 31 g stone that is partially covered with a dull black fusion crust.
Petrography: (T. Bunch and J. Wittke, NAU) Protogranular texture with several poikilitic grains of orthopyroxene host and rounded olivine inclusions. Mineral modes (vol%): orthopyroxene, 94; olivine, 4; chromite, metal and FeS, 2.
Mineral compositions and geochemistry: orthopyroxene (Fs24.3Wo3.7; FeO/MnO = 28), olivine (Fa30.3; FeO/MnO = 45), chromite (Cr/(Cr+Al) = 0.66), metal (Ni = 3.1 wt%).
Classification: Achondrite (diogenite). Low weathering grade and low shock level.
Type specimen: A 7 g sample is on deposit at NAU. The main mass holder is anonymous.

AP 004. Protogranular texture of curved to linear grain boundaries with 96 vol% opx, 3 % chromite, and 1 % olivine. Base width = 7 mm; crossed polarizers. Image © T. E. Bunch, 2007.


Dhofar 1269 (18°43'53"N 54°30'33"E)

Oman
Find: 2005
Achondrite (diogenite, polymict breccia)

History and physical characteristics: A dark brown, 42 g stone was found in the Dhofar region of Oman by Eric Olson on March 4, 2005.
Petrography: (T. Bunch and J. Wittke, NAU) A polymict breccia that contains two distinct lithologies: (A) coarse-grained orthopyroxene (<5 mm fragment size), plagioclase, and chromite. (B) Partially brecciated gabbro (olivine orthopyroxenite) containing cumulate olivine + orthopyroxene + chromite with plentiful inclusions of FeS. Modal analyses of lithology B made on 4 clasts (vol%): orthopyroxene = 48-65, olivine = 31-49, FeS = 3-5 and chromite = 1.
Mineral compositions and geochemistry: Lithology A: orthopyroxene (Fs21.9Wo2.8; FeO/MnO = 31, chromite (Cr/(Cr+Al) = 0.70). Lithology B: Orthopyroxene (Fs23.8Wo3.2; FeO/MnO = 29), olivine (Fa29.1; FeO/MnO = 48), chromite (Cr/(Cr+Al) = 0.53), FeS (contains 0.45 wt% Zn and 0.38 wt% Ti), metal (2.8 wt% Ni).
Classification: achondrite (diogenite, polymict breccia), Weathering grade is low as is the shock level.
Type specimen: An 8.4 g sample is on deposit at NAU. E. Olson holds the main mass.


Northwest Africa 2047

Morocco
Found 2003
Achondrite (diogenite, polymict)

NWA 2047. Image © T. E. Bunch, 2004

A 57.73 g, fully crusted and oriented stone, was purchased in Rissani, Morocco, September 2003. Classification and mineralogy (T. Bunch and J. Wittke, NAU): diogenite polymict breccia; modal analyses: diogenite clasts, 91 vol%; basaltic eucrite clasts, 3 % cumulate eucrite clasts, 3 %; shock-melt clasts, 3 %. Shock level, S3-4: maskelynite, PDFs and reduced birefringence in pyroxenes. Diogenite orthopyroxene, Fs23.7Wo2.3 to Fs35Wo3; Fe/Mn = 29.3 to 34.6; exsolved augite, Fs2.8Wo44. Minor olivine, Fa38.8; metal, Ni = 1.03, Co = 0.63. Also minor plagioclase, phosphate, sulfides, ilmenite, and basaltic eucrite components. Very low weathering grade. Specimens: 7.0 g, NAU; main mass, Farmer.

NWA 2047. Image © T. E. Bunch, 2004


Northwest Africa 2048

Morocco
Find: 2003
Achondrite (diogenite, monomict)

NWA 2048. Image © T. E. Bunch, 2004

History: A single stone was found in Morocco and purchased in Rissani, Morocco, September 2003.
Physical characteristics: The 44.5 g, buff-colored stone is partially fusion crusted with moderate desert etching.
Petrography (J. Wittke and T. Bunch, NAU): Monomict breccia with ~ 2mm sized orthopyroxene porphyroclasts that are surrounded by recrystallized matrix. Very small (< 0.05 mm) olivine, chromite, troilite, plagioclase, and ilmenite grains are scattered throughout the orthopyroxene matrix. The stone is moderately weathered and lightly shocked.
Geochemistry: Orthopyroxene compositions are tightly clustered around Fs25Wo2, FeO/MnO = 34.6; with minor olivine, Fa28.7, FeO/MnO = 51; plagioclase, An83; chromite, cr# = 68.
Classification: Achondrite (diogenite, monomict breccia).
Type Specimens: A 9.71 g sample is on deposit at NAU; Farmer is the main mass holder.

NWA 2048. Image © T. E. Bunch, 2004


Northwest Africa 2059

Morocco
Found 2003
Achondrite (diogenite, polymict)

NWA 2059 Image © T. E. Bunch, 2004

A 36 g partially crusted and complete stone was purchased in Erfoud, July 2003. Classification and mineralogy (J. Wittke and T. Bunch, NAU): plentiful, angular orthopyroxene clasts of considerable compositional range (Fs17.7-47.5Wo1.9-4.2) and a few large plagioclase clasts (An81-91.6) together with sparse cumulate and basaltic eucrite clasts. Clast modes: diogenite, 87 vol%; eucrite, 11 vol% and shock clasts, 2 vol%. Cumulate basaltic pyroxenes average Fs41.6Wo24.6. Very small metal inclusions (<0.01 mm) in diogenite pyroxenes have very low Ni (<0.57 wt%) contents. Overall shock level, S2; very little weathering. Specimens: type specimen 7.3 g, NAU; main mass, Boswell.

NWA 2059. © T. E. Bunch, 2004


Northwest Africa 2081

Morocco
Found 2003
Achondrite (diogenite)

NWA 2081. © T. E. Bunch, 2004

Two mostly complete stones (114 g) were purchased in Rissani, Morocco in October 2003. Description and classification (T. Bunch and J. Wittke, NAU): monomict breccia composed of partially recrystallized orthopyroxene clasts set in a fine to medium grained matrix of crushed orthopyroxene. Mineral modes (vol%): orthopyroxene, 95; olivine, 4; chromite, 1; metal and sulfide, <1. Orthopyroxene commonly exhibits fine deformation lamellae that are parallel to the [001] zone axis. Orthopyroxene, Fs23.3Wo2.1; olivine, Fa6.9; chromite, Mg/(Mg+Fe) = 0.22, Cr/(Cr+Al) = 0.86. Shock level, S2/3; very low weathering grade (no oxidation of metal and no staining). Specimens: 22.2 g plus one thin section, NAU; main mass, Farmer.

NWA 2081. Image © T. E. Bunch, 2004


Northwest Africa 2115

Northwest Africa
Purchased January 2004
Achondrite (olivine diogenite)

A partially crushed stone of 642.3 g was purchased from a dealer in Erfoud, Morocco. Description and classification (T. Bunch and J. Wittke, NAU): Yellowish green to brown, friable olivine diogenite. Very large olivine phenocrysts (up to 18.5 mm in longest dimension) and orthopyroxene (up to 11 mm) remain in a highly crushed, grainy matrix; millimeter-sized chromite is also visible in the hand specimen. Unzoned olivine, Fa27.7; FeO/MgO = 45.4; orthopyroxene, Fs22.9Wo1.5; FeO/MnO = 26.9; chromite, Cr/(Cr+Al) = 88.6; Mg/(Mg+Fe) = 18.4. Also contains minor metal (Ni = 0.29 wt%; Co = 0.59 wt%) and troilite. No plagioclase was observed. Modal analyses, based on 90 mm2, give 47 vol% olivine, 49 vol% orthopyroxene, 3 vol% chromite and <1 % troilite and metal. Shock level, S3, weathering grade, W2. Likely paired with NWA 1877. Specimens: 21.3 g, NAU; main mass, Oakes.

NWA 2115. Image © T. E. Bunch, 2004


Northwest Africa 2198

Northwest Africa
Find: 2005
Achondrite (diogenite)

History and physical characteristics: A 30g, complete stone was purchased from a dealer in Erfoud, Morocco in 2005 by Dr. David Gregory. The stone is fully crusted stone with a dull, dark luster.
Petrography (J. Wittke and T. Bunch, NAU): Brecciated diogenite that contains (in vol%): orthopyroxene (91), olivine (3), Ca-pyroxene (2), chromite (2), plagioclase (1) and FeS and metal (1). Small amounts of calcite and siderite are found in small fractures, weathering grade is low.
Mineral compositions: orthopyroxene, Fs23.2Wo3.3 (FeO/MnO = 46); olivine, Fa29.3 (FeO/MnO = 26); plagioclase, An86.5; chromite, Cr/(Cr+Al) = 0.77; metal Ni = 1.7 wt% Ni.
Classification: Achondrite (diogenite).
Type specimen: A total of 6 g is on deposit at NAU. Dr. David Gregory holds the main mass.

NWA 2198. Thin-section width is 23 mm. Image © T. E. Bunch, 2008


Northwest Africa 2434

Northwest Africa
Purchased 2004
Achondrite (diogenite, metal-rich)

A 441 g partially crusted stone was purchased in Erfoud, Morocco. Description and classification (J. Wittke and T. Bunch, NAU): highly brecciated, metal-rich diogenite with orthopyroxene fragments up to 11 mm in size and scattered recrystallized pockets. Modal content in vol%: orthopyroxene, 86.2; metal, 7.3 (heterogeneously distributed, 4.3 to 13.2 vol%); plagioclase, 5.5, phosphate, sulfide and chromite <2. Orthopyroxene, Fs24.2Wo1.3 (FeO/MnO = 32.7); Ca-rich pyroxene, Fs8Wo46.9; plagioclase, An95.7; chromite, cr# = 69; metal, Ni = 6.5 wt%. Very fresh; shock level, S2. Specimens: type specimen, 27.6 g, NAU; main mass, Hall.

NWA-2434. Base width = 13 mm. Image © T. E. Bunch, 2007.


Northwest Africa 2629

Northwest Africa
Purchased 2004
Achondrite (diogenite)

A 244 g uncrusted, partial stone was purchased in Erfoud, Morocco. Description and classification (J. Wittke and T. Bunch, NAU): yellowish-green to brown, friable olivine-rich diogenite with orthopyroxene grains up to 21 mm in size; rare, unzoned olivine. Fa28 (FeO/MnO = 44). Orthopyroxene, Fs23.4Wo1.5 (FeO/MnO = 24.9); chromite, cr# = 87, mg# = 19.4. Also contains metal (Ni = 0.29 wt%) and troilite. Shock level is S2-3 and lightly to moderately weathered. Likely paired with NWA 1877. Specimens: type specimen, 22 g, NAU; main mass, Farmer.

NWA-2629. Base width = 9 mm. Image © T. E. Bunch, 2007.


Northwest Africa 2795

Northwest Africa
Purchased 2005
Achondrite (diogenite)

History: A 329 g partial stone with moderately weathered fusion crust was purchased in Erfoud, Morocco, in 2005.
Petrography: (J. Wittke and T. Bunch, NAU) Brecciated fine to coarse grain size (<1 cm).
Geochemistry: Orthopyroxene (Fs26.2Wo2.5; FeO/MnO = 29.5), minor Ca-rich pyroxene (Fs18.5Wo28.8), plagioclase (An87.7), chromite (Cr/(Cr+Al) = 0.79), ilmenite, and kamacite present.
Classification: Achondrite (diogenite), moderately shocked (some maskelynite and high strain in orthopyroxene).
Specimens: A 20.4 g type specimen is on deposit at NAU. G. Hupé holds the main mass.

NWA-2795. Base width = 17 mm. Image © T. E. Bunch, 2007.


Northwest Africa 2824

Northwest Africa
Find 2005
Achondrite (diogenite)

History and physical characteristics: A 485 g stone was purchased from a European meteorite dealer in 2005. The stone shows moderate surface weathering with little remaining fusion crust.
Petrography (T. Bunch and J. Wittke, NAU): A highly shocked and brecciated diogenite that is plagioclase rich. Most of the smaller pyroxenes have recrystallized into polygonal mosaics, grains larger than one mm show mechanical twinning, PDFs, reduced birefringence and annealed reaction grain margins. Plagioclase recrystallized into complex spherulitic textures. Modal analyses (vol%): orthopyroxene, 80; plagioclase, 18; metal and FeS, 2.
Mineral compositions: Orthopyroxene, Fs31.2-33.8Wo3.1-3.8; reaction rim orthopyroxene, Fs20Wo3.3; plagioclase, An96.3-98.8; Ni in FeS = 2-3.4 wt%.
Classification: Achondrite (diogenite).
Type specimen: A total of 34 g is on deposit at PSF. The main mass holder is anonymous.


Northwest Africa 2923

Northwest Africa
Found 2005
Achondrite (diogenite polymict breccia)

History: A 606 g complete stone fully crusted with moderately fresh fusion crust was purchased in Erfoud, Morocco, in July 2005.
Physical Characteristics: (T. Bunch and J. Wittke, NAU) A light buff-color interior matrix with clear, yellow, green, dark diogenite clasts.
Petrography: Modal analyses of a 27 cm2 surface area: diogenites (grain size <2.7 cm) = 83, olivine microbasalts = 6, shock melt clasts = 5, recrystallized cumulate basalts = 4, chromite, sulfide, ilmenite, metal = 2 (all vol%).
Geochemistry: Diogenite: Orthopyroxenes (Fs22-27.6Wo2.9; FeO/MnO = 28-31). Unique olivine microbasalt clasts: olivine (Fa33.6; FeO/MnO = 54; these are microphenocrysts <0.48 mm in diameter), orthopyroxene (<0.2 mm) (Fs27.7Wo2.8; FeO/MnO = 27) with <0.05 mm diameter grains of vermicular metal (Ni = 6.2 wt%), and FeS (Cr = 6.2 wt%); minor diopside (Fs10.0Wo45.7).
Classification: Achondrite (diogenite, polymict breccia); low to high (recrystallized melts) shock, minimal weathering.
Specimens: A 50 g type specimen is on deposit at NAU. Farmer holds the main mass.

NWA-2923. Base width = 15 mm. Image © T. E. Bunch, 2007.


Northwest Africa 2997

Algeria
Found 2006
Achondrite (diogenite, unbrecciated)

History: A complete stone was purchased in Erfoud, Morocco in July 2006 and sold to an anonymous buyer in Sept. 2006.
Physical characteristics: A brownish 43 g stone with no remnant fusion crust.
Petrography (T. Bunch and J. Wittke NAU): Unbrecciated, cumulate-textured diogenite with well-developed preferred orientation of orthopyroxene grains. Large orthopyroxene oikocrysts (up to 8 mm in longest dimension) surround smaller orthopyroxene grains of similar composition that have long axis deviations from the oikocryst orientation axis. Grain boundaries of all orthopyroxene grains are scalloped to serrated. Sparse, large chromite crystals (up to 2.5 mm) are surrounded in "necklace" fashion by small olivine grains (< 0.2 mm) and contain tiny inclusions (< 0.03 mm) of aluminous orthopyroxene, diopside, a silica phase, pigeonite, K-feldspar, plagioclase, metal, and FeS. With the exception of feldspars, all of these phases are also found as very small inclusions in host orthopyroxenes.
Geochemistry: Orthopyroxene, Fs22.1-24.3Wo3.0, FeO/MnO = 29-32; chromite, Cr/(Cr+Al) = 0.78, "necklace" olivine, Fa21.2-24.5, FeO/MnO = 45-56. Inclusion phases: diopside, Fs10.5Wo41.4, pigeonite, Fs20Wo11.5; K-feldspar, An10.4Or42; plagioclase, An77.6 and metal, Ni = 0.56 wt%.
Classification: Achondrite (unbrecciated cumulate diogenite). The stone is lightly weathered and lightly shocked (blocky, domain extinction). This meteorite is very similar to NWA 4215 in many mineralogical characteristics, but differs greatly in orthopyroxene grain size.
Type specimens: A 10 g sample and one thin section are on deposit at NAU. The main mass holder is anonymous.

NWA 2997. Partial cross-polarized light photomicrograph. Low interference colors = orthopyroxene; higher colors = olivine; black = chromite. Image width 14 mm. © T. E. Bunch, 2004


Northwest Africa 3106

Morocco
Found 2003
Achondrite (diogenite)

NWA 3106. Image © T. E. Bunch, 2004

A single, 130 g complete stone was purchased in Rissani in December, 2003. Description and classification (T. Bunch and J. Wittke, NAU): brecciated, monomict diogenite with subrounded clasts that range from shock level S2 to S4; metal-rich (metal = 11.7 vol%). Low-Ca pyroxene shows a narrow compositional range in all clasts and matrix: Fs30.0-30.7Wo3.4-3.9, Fe/Mn = 23.8-26.6; plagioclase, An94.2; kamacite, Ni = 5.9 wt%; taenite, Ni = 39.9 wt%. Low weathering grade, slight oxidation and staining. Specimens: 20.4 g, NAU; main mass, Oakes.

NWA 3106. Image © T. E. Bunch, 2004


Northwest Africa 4283

Algeria
Found 2005
Achondrite (diogenite)

History: A 254 g stone was found in the southern desert of Algeria and sold in Erfoud, Morocco, in December 2005.
Physical characteristics: A light blue-gray stone with no remnant fusion crust and a highly irregular outer surface. Contains large orthopyroxene crystals up to 2.7 cm in longest dimension. Large euhedral chromite crystals (~1-3 mm) extend outward from the surface as a result of differential eolian ablation.
Petrography (T, Bunch and J. Wittke, NAU): In addition to the large chromite crystals, orthopyroxene contains stringers of tiny subhedral chromite together with FeS grains and rare metal that is mantled by light Fe oxide staining.
Geochemistry: The stone is mostly orthopyxoxene (96.2 vol%) with chromite, FeS, and metal (3.8 vol%). Orthopyroxene is Fs23.4Wo2.4, FeO/MnO = 26, Chromite, Cr/[Cr+Al] = 0.85 and metal contains 0.46 wt% Ni. Weathering effects are low and the shock level is S2.
Classification: Chondrite (diogenite).
Type specimens: a total of 28 g and one thin section are on deposit at NAU. Thompson is the main mass holder.

NWA 4283. Large-grained orthopyroxene with cross - cutting cataclastic veins and dark chromite inclusions. Width = 3.3 cm. Image © T. E. Bunch, 2004

NWA-4283. Base width = 17 mm. Image © T. E. Bunch, 2007.


Northwest Africa 4285

Algeria
Found 2005
Achondrite (diogenite)

History and physical characteristics: A 48 g buff -colored stone with fresh, black fusion crust was purchased in Erfoud, Morocco, in December 2005.
Petrography (J. Wittke and T. Bunch, NAU): coarse-grained breccia of fragments up to 1.8 cm with interstitial cataclastite. Mineral modes in vol% are: orthopyroxene 88, olivine 5, chromite 3, plagioclase 2, and FeS plus metal 2.
Geochemistry: Orthopyroxene Fs24.5Wo3.7, FeO/MnO = 26; olivine Fa29.1, FeO/MnO = 54; plagioclase An88, chromite Cr/(Cr+Al) = 0.68; troilite Cr content = 2.2 wt% and metal Ni content = 1.15 wt%.
Classification: Achondrite (diogenite, olivine, and plagioclase-bearing); S3, minimal weathering.
Type specimens: A total of 10 g and one thin section are on deposit at NAU. Thompson is the main mass holder.

NWA-4285. Base width = 13 mm. Image © T. E. Bunch, 2007.


Northwest Africa 4654

Algeria
Find: 2006
Achondrite (diogenite)

History and physical description: A 49 g buff-colored stone with patchy, fresh fusion crust was found in Algeria in 2006 and purchased in Erfoud, Morocco by A. Aaronson in July 2006.
Petrography: (J. Wittke and T. Bunch, NAU) Coarse-grained orthopyroxene (< 7 mm in dia.) enclose large chromite grains (one to 2.6 mm). Tiny troilite grains (< 0.02 mm) are widespread in the matrix.
Mineral compositions and geochemistry: orthopyroxene (Fs21.6-22.6Wo1.7-2.1), chromite (Cr/(Cr+Al) = 0.79).
Classification: Achondrite (diogenite0, lightly weathered and lightly shocked.
Type specimen: a 10.2 g specimen is on deposit at NAU. A. Aaronson holds the main mass.

NWA-4654. Base width = 14 mm. Image © T. E. Bunch, 2008.


Northwest Africa 4664

Algeria
Find: 2006
Achondrite (polymict diogenite breccia)

History and physical characteristics: Many stones that weigh ~20 kg were purchased in Rissani, Morocco in July 2006 by A. Aaronson and are part of a large strewn field in which at least 30 kg have been recovered.
Petrography (T. Bunch and J. Wittke, NAU): a moderately shocked diogenite cataclastic breccia. Samples range from very matrix rich to those that are matrix-poor and are composed of closely packed clasts. Mineral modes (vol%): orthopyroxene = 92, olivine = 4, plagioclase = 2, augite = 2, chromite and FeS = 1. Trace amounts of silica and metal are also present. The sample has as least two lithologies: one contains orthopyroxene with lowest FeO and without olivine; the other contains olivine with slightly more FeO-rich orthopyroxene. Orthopyroxene grains show minor amounts of shock lamellae and well-developed undulatory extinction. Plagioclase is partially isotropic.
Mineral compositions and geochemistry: Orthopyroxene (Fs17.8-23Wo1.1-2.8; FeO/MnO = 30-37), olivine (Fa24.1-32.6; FeO/MnO = 52-56), plagioclase (An79), chromite (Cr/(Cr+Al) = 0.67).
Classification: Achondrite (polymict diogenite breccia). Most likely paired with NWA 4473. Weathering is low to moderate and the shock level is moderate.
Type sample: A 34 g sample is on deposit at NAUA. Aaronson holds the main mass.


Northwest Africa 5149

Morocco
Find: 2007
Achondrite (diogenite)

NWA-5149. Base width = 12 mm. Image © T. E. Bunch, 2010.

NWA-5149. Base width = 6 mm. Image © T. E. Bunch, 2010.


Northwest Africa 5208

Morocco
Find: 2007
Achondrite (diogenite)

History and physical characteristics: A very fresh 245 g stone was purchased in Morocco in 2007. The stone is partially crusted with fresh melt flow lines.
Petrography (T. Bunch and J. Wittke, NAU): A breccia that mostly consists of fresh, light yellow green diogenite fragments with minor eucrite basaltic and cumulate clasts (vol% = 6) and shock-melt clasts (vol% = 6). Chromite, metal, ilmenite and small maskelynite fragments are present in the matrix.
Geochemistry: Diogenite orthopyroxenes, Fs2334Wo1.9-2.5 (FeO/MnO = 27-34). Eucrite orthopyroxene, Fs57Wo4.6; augite, Fs8.5Wo43.1; chromite Cr/(Al+Cr) = 0.90, metal Ni = 0.8-6.4 wt%, and maskelynite is An91-94.7.
Classification: Achondrite (diogenite).
Type specimen: A total of 20.5 g is on deposit at NAU. Mr. A. Aaronson holds the main mass.


Northwest Africa 5312

Rich, Morocco
Find: 2007
Achondrite (olivine diogenite)

History and physical characteristics: A 354 g partially crusted stone was purchased in Rich, Morocco in 2007. The fusion crust is moderately weathered with a dark brown coloration of the uncrusted surface.
Petrography (T. Bunch and J. Wittke, NAU): An unusual brecciated olivine diogenite (olivine-orthopyroxenite) that contains a large amount of troilite and olivine. Modal analyses are (in vol%): orthopyroxene, 46; olivine, 24; troilite 18; apatite, 6 chromite, 4; and taenite, 2. Breccia clasts of orthopyroxene and olivine are as large as 3.5 mm and are surrounded by either fine-grained, polygonized orthopyroxene + olivine + apatite + chromite + FeS or symplectic intergrowths of these minerals. A few orthopyroxene grains are poikilitic with olivine chadacrysts. Low weathering grade and moderate shock level of S3.
Mineral compositions: Orthopyroxene is Fs20.6Wo1.5 (FeO/MnO = 31); olivine is Fa22.1 (FeO/MnO = 48); chromite Cr/(Cr+Al) = 0.73; taenite Ni = 42.5 and merrillite MgO = 3.6 wt%.
Oxygen isotopes: (D. Rumble, CIW) replicate analyses by laser fluorination gave: δ17O, 1.545 and 1.484; δ18O, 3.364 and 3.149: Δ17O, - 0.2242 and -0.1728.
Classification: Achondrite (olivine diogenite).
Type specimen: A total of 21.1 g are on deposit at PSF. The main mass holder is anonymous.

NWA-5312. Base width = 14 mm. Image © T. E. Bunch, 2010.


Northwest Africa 5315

Erfoud, Morocco
Find: 2007
Achondrite (diogenite, anomalous)

History and physical characteristics: A 35 g crusted stone of minor surface weathering was purchased in Erfoud, Morocco in 2007.
Petrography (J. Wittke and T. Bunch, NAU): An unusual feldspathic diogenite breccia. Modal analyses (vol%): orthopyroxene, 74; plagioclase, 20; silica glass, 3; metal, chromite, and FeS, 3. Shock level is S3-4, plagioclase is partially converted to maskelynite. Weathering is low grade.
Mineral compositions: Orthopyroxene is Fs33Wo3.6 (FeO/MnO = 33); plagioclase is An93.9; chromite Cr/(Cr+Al) = 0.81 and metal Ni = 2.1 wt%.
Classification: Achondrite (diogenite, anomalous). The unusually high plagioclase content gives this diogenite a distinctive characteristic.
Type specimen: A total of 7 g is on deposit at PSF. The main mass holder is anonymous.

NWA-5315. Base width = 6 mm. Image © T. E. Bunch, 2010.