Martian Meteorite NWA 13250 - Poikilitic Shergottite (Peridotitic - Lherzolitic)

Description

NWA 13250
NWA 13250
Planetary Achondrite,
Martian
Poikilitic Shergottite (Peridotitic - Lherzolitic)
Specimen is a 5.87g full slice
(Origin Craig Zilmen)
*
Poikilitic
texture refers to igneous rocks where large component crystals contain smaller crystals of other minerals within them. In poikilitic rocks, the contained smaller crystals are termed 'chadacrysts' (here the olivine, the shock darkened crystals) and the larger phenocrysts are termed 'oikocrysts' (here the pyroxene, apple green colored).
The paired meteorite  NWA 13367 have been described accordingly by its classifier (Carl Agee, University of New Mexico) as
structurally poikilitic indeed, but
he went to submit them to the Nomenclature Comittee of the Meteoritical Societyn as
describing the proposed nature of the rock as well
:
*
peridotitic
*
Peridotite
is a dense, coarse-grained mostly mantelic igneous rock consisting predominatly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from the mantle of a planetary parent body, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle.
Northwest Africa 13250
Basic information
Name:
Northwest Africa 13250
This is an OFFICIAL meteorite name.
Abbreviation:
NWA 13250
Observed fall:
No
Year found:
2019
Country:
Mauritania
Mass:
2.57 kg
Classification
history:
Recommended:
Martian (shergottite)
Comments:
Approved 28 Mar 2020
Writeup
Writeup from MB 109:
Northwest Africa 13250
(NWA 13250)
Mauritania
Purchased: 2019 Dec
Classification: Martian meteorite (Shergottite)
History
: Purchased from a Mauritanian meteorite (and desert truffle) hunter.
Physical characteristics
: Single stone; saw cut reveals an ultramafic cumulate rock with ophitic to poikilitic textures with mm-size pale yellow and dark gray grains.
Petrography
: (C. Agee,
UNM
) Microprobe examination shows approximately 50% olivine, 40% pyroxene, and 5-10% maskelynite. Two distinct pyroxene trends are present 1) Mg-rich low calcium pyroxene trending to slightly more Fe-rich pigeonite, 2) Mg-rich augite trending to diopsidic. Three distinct Cr-Fe spinel phases were detected throughout the sample, one with high TiO
2
(~14 wt%), one with intermediate TiO
2
(~7.5 wt%), and one with very low TiO
2
concentrations. Ilmenite and Fe-sulfide are minor ubiquitous phases.
Geochemistry
: (C. Agee,
UNM
) Olivine Fa
34.3±2.4
, Fe/Mn=50±3, n=7; low Ca-pyroxene Fs
24.6±2.8
Wo
7.3±2.1
, Fe/Mn=30±1, n=11; augite Fs
15.8±1.1
Wo
38.5±5.6
, Fe/Mn=25±1, n=5.
Classification
: Martian peridotitic shergottite. Macroscopic textural appearance similar to
NWA 1950
and
ALHA77005
.
Specimens
: 22.7 g on deposit at
UNM
,
DPitt
holds the main mass.
Data from:
MB109
Table 0
Line 0:
Date:
P 2019 Dec
Mass (g):
2572
Pieces:
1
Class:
Martian (shergottite)
Shock stage:
high
Weathering grade:
moderate
Fayalite (mol%):
34.3±2.4
Ferrosilite (mol%):
24.6±2.8, 15.8±1.1
Wollastonite (mol%):
7.3±2.1, 38.5±5.6
Classifier:
C. Agee, UNM
Type spec mass (g):
22.7
Type spec location:
UNM
Main mass:
DPitt
Comments:
Field name MVCH487; submitted by C. Agee, UNM
Institutions
and collections
UNM
: Institute of Meteoritics MSC03 2050 University of New Mexico Albuquerque NM 87131-1126 USA, United States;
Website
(institutional address; updated 12 Feb 2015)
DPitt
: Darryl Pitt, 225 West 83rd Street, New York, NY 10024, United States;
Website
(private address)
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