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Northwest Africa 13270
Basic information Name: Northwest Africa 13270
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 13270
Observed fall: No
Year found: 2019
Country: Algeria
Mass:help 33 g
Classification
  history:
Recommended:  LL3.5    [explanation]

This is 1 of 22 approved meteorites classified as LL3.5.   [show all]
Search for other: LL chondrites, LL chondrites (type 3), Ordinary chondrites, and Ordinary chondrites (type 3)
Comments: Approved 9 May 2020
Writeuphelp
Writeup from MB 109:

Northwest Africa 13270 (NWA 13270)

Algeria

Find: 2019 Feb 7

Classification: Ordinary chondrite (LL3.5)

History: Found by nomads in Algeria on 7 Feb 2019, purchased by Stephen Amara from Mustapha Hnini in Tindouf on 10 Oct 2019.

Physical characteristics: Single stone with dark-brown fusion crust.

Petrography: (D. Sheikh, FSU; A. Love, App) Sample is a chondrite composed of well-defined chondrules (Av. 815±50 μm, range 250-1802 μm, n=37) and a few dark, fine-grained inclusions (<5mm) set in an opaque matrix. Devitrified mesostasis is present in most chondrules while isotropic glassy mesostasis is relatively rare. Many chondrules are armored with sulfides and contain rounded globules of FeNi metal. (A. Love, App) Optical CL: Sample exhibits bright and distinct CL. Sample is dominated by chondrules with olivine displaying dull red luminescence (A5) and blue to blue-purple mesostasis (B2, B3), however the sample does contain 5% A2 chondrules. Chondrules with bright red luminescence lack the prominant CL zoning seen in lower petrologic types. Chondrule rims and matrix show dim, dark red and blue CL (>type 3.4, <type 4).

Geochemistry: (D. Sheikh, FSU) Olivine (Fa18.2±11.1, range Fa1.6-45.0, CaO wt% =0.11±0.07, n=42), Cr2O3 in ferroan olivine (0.06±0.04 wt%, range 0.01-0.26, n=32), Low-Ca Pyroxene (Fs9.6±6.2 Wo0.5±0.4, range Fs1.0-23.4 Wo0.2-1.5, n=21).

Classification: Ordinary Chondrite (LL3.5) LL group is due to average chondrule diameter and magnetic susceptibility. Subtype 3.5 is due to numerous reasons: 1) While devitrified mesostasis may be more dominant in the chondrules, there is still primary isotropic glassy mesostasis contained within some chondrules as evident by the 5% of A2 chondrules (Dehart et al. 1992). 2) The Cr2O3 values and standard deviations for ferroan chondrule olivines plot in the 3.2 field for UOCs. 2) The measured fayalite and CaO values for chondrule olivines indicate a petrologic type <3.8 (Huss et al. 2006). Overall, the presence of primary glassy mesostasis and ferroan olivine containing low subtype Cr2O3 values in a small percentage of chondrules (5%) indicates that the peak metamorphic temperature or duration during thermal metamorphism of the sample was not enough to fully devitrify the primary glassy chondrule mesostasis throughout all of the chondrules, one of the observed features for subtype 3.6 (Dehart et al. 1992). Therefore, this sample is estimated to have a subtype of 3.5.

Specimens: 7.65 grams at UCLA; main mass with Stephen Amara.

Bibliography:
  • DeHart J.M., Lofgren G.E., Lu J., Benoit P.H., and Sears D.W.G. (1992) Chemical and physical studies of chondrites: X. Cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites. Geochim. Cosmochim. Acta56, 2791-3807 (link)
Data from:
  MB109
  Table 0
  Line 0:
Date:2019 Feb 7
Mass (g):33
Pieces:1
Class:LL3.5
Shock stage:S3
Weathering grade:W1
Fayalite (mol%):18.2±11.1 (N=42)
Ferrosilite (mol%):9.6±6.2 (N=21)
Wollastonite (mol%):0.5±0.4 (N=21)
Magnetic suscept.:4.52
Classifier:D. Sheikh, FSU; A. Love, App
Type spec mass (g):7.65
Type spec location:UCLA
Main mass:Stephen Amara
Comments:Submitted by Daniel Sheikh
Institutions
   and collections
UCLA: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, United States (institutional address; updated 17 Oct 2011)
App: Department of Geology, 572 Rivers St., Appalachian State University, Boone, NC 28608, United States (institutional address; updated 7 Mar 2013)
FSU: Department of Geological Sciences, Florida State University, Tallahassee FL 32306-4100, United States (institutional address; updated 16 Dec 2010)
Catalogs:
References: Published in Meteoritical Bulletin, no. 109, in preparation (2020)
Find references in NASA ADS:
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Photos:
CreditPhotos
Public domain photographs:
Daniel Sheikh   
Geography:

Algeria
Coordinates:Unknown.

Statistics:
     This is 1 of 1003 approved meteorites from Algeria (plus 26 unapproved names) (plus 4 impact craters)

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