|Northwest Africa 7402|
|Basic information||Name: Northwest Africa 7402|
This is an OFFICIAL meteorite name.
Abbreviation: NWA 7402
Observed fall: No
Year found: 2010
Country: (Northwest Africa)
Mass: 4.01 kg
This is 1 of 15 approved meteorites classified as L3.1. [show all]
Search for other: L chondrites, L chondrites (type 3), Ordinary chondrites, and Ordinary chondrites (type 3)
|Comments:||Approved 24 Jan 2015|
Writeup from MB 104:
Northwest Africa 7402 (NWA 7402)
Purchased: 2010 August 26
Classification: Ordinary chondrite (L3.1)
History: NWA 7402 was purchased on August 26, 2010, by Eric Twelker from a meteorite trader in Morocco.
Physical characteristics: A 4013.4 g individual stone, with fusion crust intact and partially rusted. Rust-colored, apparently weathered areas with orange-brown chondrules surround less-weathered regions containing light-gray chondrules set within a darker gray groundmass. The meteorite is a breccia, with occasional clasts of different lithologies present (up to ~5 mm width). The transition from weathered to unweathered lithology is abrupt, and does not correlate with clast boundaries.
Petrography: (C. E. Jilly-Rehak, UH) Transmitted and reflected light optical microscopy reveal a high abundance of chondrules embedded in a clastic, sulfide-rich matrix. Chondrules range from ~0.2 - 2 mm in apparent diameter, and an anomalously large barred olivine chondrule of 8 mm exists in one thin section. Chondrule types found in the meteorite include porphyritic olivine, barred olivine, porphyritic pyroxene, radial pyroxene, and cryptocrystalline. The porphyritic olivine chondrules comprise both type I (Fa<2) and type II (Fa10-25). Fine-grained FeO-rich silicate rims are observed surrounding some (but not all) chondrules. The rims are typically embedded with μm-sized Fe sulfides. The matrix contains abundant Fe,Ni metal and sulfides, as well as chondrule fragments and isolated silicate grains. Large opaque assemblages (~300 μm in diameter) are found in the matrix, containing both kamacite and taenite, Fe sulfides, and Fe oxides. Optical microscopy reveals moderate shock and weathering, corresponding to maximum stages S2 and W2, respectively. The studied sections do not contain any calcium-aluminum inclusions (CAIs), although one aluminous chondrule was found. The pre-weathering metal abundance could have been up to 10.7 wt%, placing the meteorite in the L-chondrite range, also in agreement with the magnetic susceptibility.
Geochemistry: Olivine is highly variable in composition, ranging from Fa<1 to Fa36 (mean, Fa12.9±8.7, N=102). Low-Ca pyroxene is Fs8.4±7.6 (N=71). Cr2O3 in 140 ferroan olivine grains is = 0.41±0.13 wt.%. Separated matrix material (<50 mg) was measured via Raman spectroscopy; peak intensities (I) for the D and G bands have FWHM=181±16 and ID/IG=0.93±0.04.
Classification: Ordinary chondrite (L3.1-anom), S2, W2. It is possibly paired with NWA 5717. Raman spectroscopy of organic matter in the fine-grained matrix indicates that the sample is petrologic type 3.1, plotting within analytical error of Bishunpur. EPMA of chromium contents in olivine shows that NWA 7402 lies between types 3.00 and 3.15, but anomalously falls off the trend for typical UOCs in Grossman and Brearley (2005). However, analyses of control specimens Semarkona and Bishunpur generally agree with the literature values. Furthermore, NWA 7402 has an elevated sulfide abundance (>15 wt%).
Specimens: The main mass of NWA 7402 (3987.9 g) is held by Twelker. The type specimen (25.5 g) is held at UNM.
UH: Hawai'i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, United States (institutional address; updated 25 Oct 2011)
UNM: Institute of Meteoritics MSC03 2050 University of New Mexico Albuquerque NM 87131-1126 USA, United States; Website (institutional address; updated 12 Feb 2015)
Twelker: Eric Twelker, P.O. Box 844, Port Townsend, WA 98368, United States; Website (private address; updated 1 Dec 2014)
|References:||Published in Meteoritical Bulletin, no. 104, in preparation (2015)|
This is 1 of 5551 approved meteorites from (Northwest Africa) (plus 2099 unapproved names)
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