Minerals and compositions:
Types 3-6 are constrained mainly on decreasing amounts of clinoenstatite with increasing orthopyroxene (orthoenstatite) and increased recrystallization of chondrules so that EL6 and EH6 chondrites have few discernable chondrules and all enstatite is orthorhombic. EH chondrites have metal >25 vol%.
Enstatite Chondrite (EL6)
A complete 305 g stone was purchased in Erfoud in January 2003. Classification and mineralogy (J. Wittke and T. Bunch, NAU): fine-grained assemblage of recrystallized enstatite and metal (25 vol. %); no relic chondrules. Enstatite, En99Wo1 (FeO <0.02 wt. %); plagioclase (Ab80Or4); metal (6.1 wt. % Ni; 0.7 wt. % Co; 0.9-1.3 wt. % Si); silica, troilite daubreelite (3.1 wt. % Mn; 0.2 wt. % Ni); alabandite (44.3 wt. % Mn; 12.9 wt. % Fe; 3.3 wt. % Mg; 0.25 wt. % Ca), and 0.7 vol. % fresh oldhamite (50.4 wt. % Ca and 1.24 wt. % Mn). Weathering grade, W0/1. Shock level, S1. Specimens: 20.1 g, NAU; main mass, Farmer.
Enstatite chondrite (EL6)
A single stone of 166 g was purchased in Erfoud, Morocco. Description and classification (J. Wittke and T. Bunch, NAU): Cataclastic, fine-grained (<0.20 mm) with very rare relict chondrule fragments. Contains orthopyroxene, Fs1.6Wo1.4; plagioclase, An5.4-11.1Or0.7-5.4; metal. Ni = 3.75 wt. %, Si = 0.93-1.45 wt. %, troilite, Ti = 3.1 wt. %, schreibersite, and daubreelite. Shock level is S2 and the weathering grade is W3 with moderate staining. Specimens: type sample, 21.3 g, NAU; main mass, Oakes.
Find: 2004 to present
Enstatite chondrite (EL3)
History: Approximately 100 kg of various sized stones were purchased by S. Turecki from Saharaoverland, Morocco in 2005. These stones were collected from the surface of a saline playa, near El Hagounia, in Western Sahara. Many 100s of kg have been recovered from the surface (NWA 2965) and from depths to less than one m (NWA 2828). The recovery field has a length of at least 40 km (pers. comm., A. Aaronson, Saharaoverland). Specimens are continuously recovered from the site.
Physical characteristics: Small to medium sized stones (< 300 g) are commonly weathered to a dark brown with irregular networks of very dark weathering veins in contrast to those excavated from depth that tend to be less iron stained. Larger pieces may retain portions of weathered fusion crust.
Petrography: (T. Bunch and J. Wittke, NAU) Mostly composed of a fine-grained matrix (<0.5 mm) of sub-rounded to prismatic crystals of nearly pure enstatite. Clusters of coarser-grained (0.5-1.2 mm) enstatite, some with plagioclase, are scattered throughout. Rare RP chondrules and fragments are found in a few slices and sections (154 cm2 visually analyzed). Tiny grains of troilite, daubreelite (as lamellae in FeS), and metal are found as inclusions in enstatite, vermicular graphite grains are found as inclusions and as larger grains in the matrix. Other minerals that are present in NWA 2828 (Kuehner et al., 2006) were not found. Severe weathering and chemical leaching have left cavities partially in-filled with a variety of secondary minerals that include carbonates, halite, gypsum, and Fe-oxides/sulfates. Shock level is low.
Geochemistry: Orthopyroxene, Fs94.4±0.02Wo0.8-1.3; plagioclase, An14.8-17.6Or4.1-4.9; FeS, Ti = 0.91 wt. %, Cr = 1.10 wt. %, Zn = 0.6 wt. %.
Classification: Enstatite chondrite (EL3). The original, erroneous classification of EL6/7 (Bull. 91) was based on two heavily altered samples, in which, the true nature of constraining characteristics were obscured. The revised classification is based on 6 thin sections and 485 g of material. Weathering grade is 4/5.
Type specimen: A total of 245 g of samples, 6 thin sections and 8 polished slices are on deposit at NAU. S. Turecki and B. Reed hold the main mass.
Kuehner, S. M., Irving, A. J., Bunch, T. E., Wittke, J. H. and Hupé, G. M. (2006) EL3 chondrite (not aubrite) Northwest Africa 2828: An unusual paleo-meteorite occurring as cobbles in a terrestrial conglomerate. Eos, Trans. Amer. Geophys. Union, 87, Fall Meet. Suppl., Abstract P51E-1247.
Enstatite chondrite (EL6)
A single 67.5 g stone was purchased in Rissani, Morocco in June 2003. Description and classification (T. Bunch and J. Wittke, NAU): completely recrystallized, fine-grained (<0.6 mm diameter) assemblage of mostly enstatite (En98.5Wo0.6Fs0.9) with minor plagioclase (An18.8Or5.1). kamacite (Ni = 6.6 wt. %; Si = 1.10 wt. %); Al-bearing SiO2 phase, graphite, alabandite (Fe = 13.4 wt. %; Mg = 2.37 wt. %); oldhamite (Fe = 0.88 wt. %) and daubreelite. Complex sulfates are also present and are probably terrestrial oxidation products. Shock stage, S2 with low-grade weathering. Specimens: 13.8 g, NAU; main mass, Oakes.
Enstatite chondrite (EL6)
History and physical characteristics: A single 339 g stone was found in the southern Algerian desert in 2006 and purchased in Erfoud, Morocco in July 2006. The stone is moderately weathered on the surface and somewhat flaky with little remaining fusion crust.
Petrography: (T. Bunch and J. Wittke, NAU) Highly recrystallized with rare, barely discernable chondule fragments. Very high metal content (28 vol. %) that is distributed throughout the matrix as small (<0. 5 mm) irregular shaped grains, as large blobs (2-4 mm) and as coarse grains (~one mm) in metal-rich recrystallized veins. Graphite is commonly included in the largest metal grains.
Mineral compositions and geochemistry: Enstatite (Fs0-0.7, many grains have < 0.02 wt. % FeO), plagioclase (An17.4), metal (Ni = 5.6-6.4 wt. %; Si = 1.15 wt. %), FeS (Cr = 1.84 wt. %; Ti = 1.18 wt. %), oldhamite (Fe = 0.65 wt. %; Mn = 0.92 wt. %; Mg = 0.48 wt. %), daubreelite (Cr = 35.6 wt. %; Fe = 15.3; Mn = 3.5 wt. %), alabandite (Mn = 3.3 wt. %; Mg = 4.9 wt. %) together with small niningerite and SiC grains.
Classification: Enstatite chondrite (EL6).
Type specimen: A 24.1 g sample is on deposit at NAU. A. Aaronson holds the main mass.
|NWA 4544||Erfoud, Morocco||2006||EL3||>200 kg||S2, W4||1-2.1||paired with NWA 2965|
|NWA 4556||Erfoud, Morocco||2006||EL3||313||S2, W4||<2||An17.5Or4.4; paired with NWA 2965|
|NWA 4561||Erfoud, Morocco||2006||EL3||>200 kg||S2, W4||<2||An16.8Or4.2; paired with NWA 2828|