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Basic information Name: Choteau
     This is an OFFICIAL meteorite name.
Abbreviation: There is no official abbreviation for this meteorite.
Observed fall: No
Year found: 2011
Country: United States
Mass:help 8.47 kg
Meteoritical Bulletin:  MB 102  (2013)  Pallasite, ungrouped
Recommended:  Pallasite, ungrouped    [explanation]

This is 1 of 12 approved meteorites classified as Pallasite, ungrouped.   [show all]
Search for other: Metal-rich meteorites, Pallasites
Comments: Approved 19 Jun 2013
Writeup from MB 102:


Montana, United States

Purchased: 2011

Classification: Pallasite (ungrouped)

History: Purchased in 2011 by Debbie Cilz at an estate sale in Choteau, Montana, and presumed to have been found locally by the deceased owner.

Physical characteristics: A single dense, brownish mass weighing 8474 g. Interior slices exhibit separated, angular clasts of olivine (~40 vol.%) within metal.

Petrography: (A. Irving and S. Kuehner, UWS) Composed predominantly of metal (kamacite with Ni-poor taenite) and large angular grains of olivine with accessory iron sulfide (pyrrhotite), schreibersite, merrillite, chromite and orthopyroxene. One large (4.5 mm) grain of exsolved calcic pyroxene was found (now composed of augite with orthopyroxene exsolution lamellae). Chromite and orthopyroxene occur in symplectitic intergrowths, and there also are small patches composed of chromite+iron sulfide+merrillite exhibiting triple grain junctions.

Geochemistry: Olivine (Fa9.2-10.1; FeO/MnO = 27-35), orthopyroxene (Fs11.2Wo0.4; FeO/MnO = 23), host clinopyroxene (Fs6.6Wo44.3; FeO/MnO = 12), orthopyroxene exsolution lamella (Fs15.3Wo1.7; FeO/MnO = 18). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed olivine by laser fluorination gave, respectively δ17O = 0.152, 0.067; δ18O = 2.502, 2.347; Δ17O = -1.169, -1.172 (all per mil).

Classification: Pallasite, ungrouped. The oxygen isotopic composition is unlike those for any other pallasites, and falls on the broad trend for acapulcoites and lodranites.

Specimens: A 20.2 g polished slice is on deposit at UWB. 94.2 g at ASU, 158 g at UNM, 80 g at TCU, 81.9 g at SI. The main mass is held by Boudreaux; additional material is held by Mr. R. Garcia and Mr. R. Cucchiara.

Data from:
  Table 0
  Line 0:
Place of purchase:Choteau
Date:P 2011
Mass (g):8474
Class:Pallasite, ungrouped
Shock stage:S1
Weathering grade:W1
Fayalite (mol%):9.2-10.1
Ferrosilite (mol%):11.2
Wollastonite (mol%):0.4
Classifier:A. Irving and S. Kuehner, UWS
Type spec mass (g):20.2
Type spec location:UWB
Main mass:T. Boudreaux
Comments:Submitted by A. Irving
Plots: O isotopes:  
   and collections
ASU: Center for Meteorite Studies, Arizona State University, Tempe, Arizona 85287-1404, United States; Website (institutional address; updated 14 Jan 2012)
SI: Department of Mineral Sciences, NHB-119, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, United States; Website (institutional address; updated 16 Jan 2012)
TCU: Oscar E. Monnig Collection, Department of Geology, Texas Christian University, Ft. Worth, TX 76129, United States; Website (institutional address; updated 24 Feb 2012)
UNM: Institute of Meteoritics MSC03 2050 University of New Mexico Albuquerque NM 87131-1126 USA, United States; Website (institutional address; updated 12 Feb 2015)
UWS: University of Washington, Department of Earth and Space Sciences, 70 Johnson Hall, Seattle, WA 98195, United States (institutional address; updated 15 Jan 2012)
UWB: University of Washington, Burke Museum of Natural History and Culture, Box 353010 Seattle, WA 98195, United States (institutional address; updated 9 Oct 2023)
Boudreaux: Terry Boudreaux, Illinois, United States (private address)
Cilz: Marlin Cilz, Montana Meteorite Lab, Box 1063, Malta, MT 59538, United States; Website (private address)
References: Published in Meteoritical Bulletin, no. 102, MAPS 50, 1662, September 2015
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United States

     This is 1 of 7 approved meteorites from Montana, United States (plus 1 impact crater)
     This is 1 of 1927 approved meteorites from United States (plus 866 unapproved names) (plus 28 impact craters)

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