NWA 13411 Anomalous Type 5 Ordinary Chondrite Meteorite 21g fragment

Description

NORTHWEST AFRICA 13411
ANOMALOUS TYPE 5 ORDINARY CHONDRITE METEORITE
CS2 W3
21 GRAM FRAGMENT
INTRODUCING A NEW ANOMALOUS CHONDRITE METEORITE WITH
REMARKABLE EXOTIC COMPOSITION
ISOTOPIC ANALYSIS SUGGESTS THIS METEORITE IS FROM A COMPLETELY NEW PARENT BODY PREVIOUSLY UNDISCOVERED UNTIL NOW
History: The 190.96g and 73.03g samples were found near Adrar, Algeria by a meteorite prospector in 2018. Dave Lehman and his partner acquired the samples from the finder.
Physical characteristics: Samples are irregular-shaped and brown. Interior of sample is orangish brown and contains abundant chondrules and weathered metal and sulfides.
Petrography: Description and Classification (A. Love, App) Sample has a chondritic texture composed of numerous close-packed equilibrated chondrules set within a recrystallized matrix. When viewed using backscattered electron imaging, the olivines and pyroxene have almost identical grey-scale colors (See Fig. 2). The sample is composed of BO, PO (dominant), PP (clinoenstatite is rare but present) and rare Al-rich chondrules with an average apparent diameter of 395±219 µm (n=131). Some pyroxenes are zoned from enstatite cores to augite rims. The sample contains secondary plagioclase with an average grainsize of 29µm (n=15). Additional minerals are: chromite, K-rich feldspar, apatite, kamacite, taenite, troilite and gypsum. Despite a comprehensive search for reduced sulfide and phosphide phases commonly associated with enstatite and forsterite chondrites, none were found in this sample.
Figs. 1 & 2.  Overview of sample (D. Lehman photo-left) and thin section viewed under cross polarized light (right).
Figs. 3 & 4 False-color X-ray images showing the abundance of magnesium (left-green) and iron (right-iron).
Shock: Olivine show sharp to weak undulatory extinction and irregular fractures. Troilite is polycrystalline.
Weathering: Sample is transected by numerous iron hydroxide veins. Surviving FeNi grains are surrounded by thick mantles of iron hydroxide minerals.
Magnetic Susceptibility: Mass magnetic susceptibility was measured using a ZH Instruments SM-30 pocket MS meter. Quadruplicate measurements of two samples produced log χ x 10-9 m3/kg= 4.97.
Geochemistry: (A. Love, App) Geochemistry of both samples was measured using the JEOL ITS300 SEM with Oxford XMax EDS in the Dewel Microscopy Lab at Appalachian State University. An accelerating voltage of 25kV was used to analyze 3 spots per grain. Compositions of olivine and pyroxene, which fall outside the field for ordinary chondrites, are equilibrated.
Olivine (Fa8.35±0.15, Fe/Mn=16.97±0.58, n=18), low-Ca pyroxene (Fs8.47±0.26Wo1.09±0.32, Fe/Mn=10.78±0.39, n=18); high-Ca pyroxene rims (Fs3.44±0.08Wo46.93±2.71, n=4). plagioclase of variable composition (Ab18.17-83.41Or0.66-12.88, n=6); FeNi metal (6.71±0.21wt% Ni and 1.09±0.02wt% Co, n=9).
Figs. 5 & 6 False color X-ray map showing one of the chondrules with multiple varieities of plagioclase (left) and backscattered electron image showing uniform grey scale colors of olivines and pyroxenes (right).
Fig. 7 Fayalite vs. Ferrosilite contents of olivines and pyroxenes (respectively) compared to a known groups of chondrites and some anomalous chondrite samples. ASU-NWA-171 appears with the red X. ASU-NWA-171 appears compositionally unique from most major chondrite groups.
Oxygen Isotopes: (Karen Ziegler, UNM) analyses of acid-washed subsamples by laser fluorination gave (all per mill): d17O=4.199, 3.277, 3.836, 3.592, 3.666, 3.102; d18O=5.891, 5.520, 6.526, 5.464, 6.433, 5.240; D17O=1.089, 0.362, 0.390, 0.707, 0.269, 0.335.
Fig. 8 Oxygen isotope compositions of ASU-NWA-171 (red X’s) compared to other ordinary chondrite groups as well as the anomalous varieties of H chondrites. NWA8691 (LL4-6), Abu Panu L3, NWA7135 chondrite ungrouped. ASU-NWA-171 plots above the field defined for “ordinary H chondrites” and overlaps the field for anomalous H chondrites and ungrouped chondrites.
Classification: Ordinary chondrite (OC-anomalous C-S2 W3) Based on chondritic texture and presence of weathered and un-weathered metal, this sample has similarities with ordinary chondrites. Based on mineral compositions and oxygen isotopes, this is an anomalous chondrite. Equilibrated compositions and grainsize of secondary plagioclase indicate this sample corresponds to petrologic type 5. Oxygen isotope compositions plot at a distance from the slope 1 line for equilibrated ordinary chondrites. Mean ∆17O composition is below the standard range for unequilibrated H chondrites and the standard deviation of the ∆17O is higher than that recorded in the entire range of unequilibrated ordinary chondrites. Co concentrations in kamacite fall between values measured in L and LL chondrites (Rubin, 1990) Based on these data, sample is an ungrouped chondrite.
Specimens: Dave Lehman and a partner hold the main masses. Two slices totaling 23.74g and a polished thin section and mount are on deposit at App.
OFFICIAL CLASSIFICATION DATA SOURCE:
The Meteoritical Society
International Society for Meteoritics and Planetary Science
Lunar and Planetary Institute
Meteoritical Bulletin Database
Northwest Africa 13411
Basic information
Name:
Northwest Africa 13411
This is an OFFICIAL meteorite name.
Abbreviation:
NWA 13411
Observed fall:
No
Year found:
2018
Country:
Morocco
Mass:
264 g
Classification
history:
Recommended:
OC5-an
[explanation]
This is the only approved meteorite classified as OC5-an.
Search for other:
Ordinary chondrites
,
Ordinary chondrites (type 4-7)
Comments:
Approved 22 Nov 2020
Writeup
Writeup from MB 109:
Northwest Africa 13411
(NWA 13411)
Western Sahara, Morocco
Purchased: 2018
Classification: OC5-an
History
: The 190.96 and 73.03 g samples were found near Adrar, Algeria, by a meteorite prospector in 2018. Dave Lehman and his partner acquired the samples from the finder.
Physical characteristics
: Samples are irregularly shaped and brown. Interior of sample is orangish brown and contains abundant chondrules and weathered metal and sulfides.
Petrography
: Description and Classification (A. Love,
App
) Sample has a chondritic texture composed of numerous close-packed equilibrated chondrules set within a comminuted matrix of the chondritic lithology. This matrix is crosscut by ubiquitous FeNiOH veinlets. When viewed using backscattered electron imaging, the olivines and pyroxene have almost identical gray-scale colors. The sample is composed of BO, PO (dominant), PP (clinoenstatite is rare but present) and rare Al-rich chondrules with an average apparent diameter of 395±219 µm (n=131). Some pyroxenes are zoned from enstatite cores to augite rims. The sample contains secondary plagioclase with an average grainsize of 29 µm (n=15). Additional minerals are: chromite, K-rich feldspar, apatite, kamacite, taenite, troilite and gypsum. Despite a comprehensive search for reduced sulfide and phosphide phases commonly associated with enstatite and forsterite chondrites, none were found in this sample.
Geochemistry
: (A. Love,
App
) Olivine (Fa
8.35±0.15
, Fe/Mn=16.97±0.58, n=18), low-Ca pyroxene (Fs
8.47±0.26
Wo
1.09±0.32
, Fe/Mn=10.78±0.39, n=18); high-Ca pyroxene rims (Fs
3.44±0.08
Wo
46.93±2.71
, n=4). plagioclase of variable composition (Ab
18.17-83.41
Or
0.66-12.88
, n=6); FeNi metal (6.71±0.21wt% Ni and 1.09±0.02wt% Co, n=9). Oxygen Isotopes: (Karen Ziegler,
UNM
) analyses of acid-washed subsamples by laser fluorination gave (all per mill): δ
17
O=4.199, 3.277, 3.836, 3.592, 3.666, 3.102; δ
18
O=5.891, 5.520, 6.526, 5.464, 6.433, 5.240; Δ
17
O=1.089, 0.362, 0.390, 0.707, 0.269, 0.335.
Classification
: Ordinary chondrite (OC5-an, C-S2, W3) Based on chondritic texture and presence of weathered and unweathered metal, this sample has similarities with ordinary chondrites. Based on mineral compositions and oxygen isotopes, this is an anomalous ordinary chondrite. Equilibrated compositions and grainsize of secondary plagioclase indicate this sample corresponds to petrologic type 5. Oxygen isotope compositions plot at a distance from the slope 1 line for equilibrated ordinary chondrites. Mean Δ
17
O composition is below the standard range for unequilibrated H chondrites and the standard deviation of the Δ
17
O is higher than that recorded in the entire range of unequilibrated ordinary chondrites. Co concentrations in kamacite fall between values measured in L and LL chondrites (Rubin, 1990).
Specimens
: Dave Lehman and a partner hold the main mass. Two slices totaling 25.08g and a polished thin section and mount are on deposit at
App
.
Data from:
MB109
Table 0
Line 0:
State/Prov/County:
Western Sahara
Date:
P 2018
Mass (g):
264.2
Pieces:
2
Class:
OC5-an
Shock stage:
C-S2
Weathering grade:
W3
Fayalite (mol%):
8.3±0.1
Ferrosilite (mol%):
8.5±0.3; 3.4±0.1
Wollastonite (mol%):
1.1±0.3; 46.9±2.7
Magnetic suscept.:
5.01
Classifier:
A. Love, App
Type spec mass (g):
25.08
Type spec location:
App
Main mass:
Dave Lehman
Comments:
Submitted by Anthony Love
Plots:
O isotopes:
Institutions
and collections
UNM
: Institute of Meteoritics MSC03 2050 University of New Mexico
App
: Department of Geology, Appalachian State University
Catalogs:
References:
Published in Meteoritical Bulletin, no. 109, in preparation (2020)
Geography:
Coordinates:
Unknown.
Statistics:
This is the only approved meteorite from
Western Sahara, Morocco
This is 1 of 1523 approved meteorites from
Morocco
(plus 22 unapproved names) (plus 1 impact crater)
Also see:
This lists the most popular meteorites among people who looked up this meteorite.
Revision
history:
This lists important revisions made to data for this record.
IMCA ( INTERNATIONAL METEORITE COLLECTORS ASSOCIATION )
I AM MEMBER # 9822  JOHN HIGGINS. THIS OFFICIALLY CLASSIFIED HIGH QUALITY METEORITE  HAS CONTRIBUTED TO THE SCIENCE OF METEORITICS THROUGH RESEARCH PERFORMED BY ANTHONY LOVE AT APPALACHIAN STATE UNIVERSITY
GUARANTEED AUTHENTICITY
Member of the Meteoritical Society & International Meteorite Collectors Association The authenticity of this meteorite has a 100% guarantee.
Signed Certificate of Authenticity Included
. First class delivery and provenance provided exhibiting important details of the classification & petrography.
1cm scale cube for reference purposes not included.
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