OUT 18018

Classification: Mesosiderite.

Explainer: This means that the sample is from a differentiated asteroid parent body. Mesosiderites are quite an unusual type of meteorite – it is a stony-iron, meaning that it is made up of roughly equal parts silicate minerals and iron metal. As of may 2021 there are only 280 meteorites that have been classified as being a mesosiderite, with only 61 of the group having been found in Antarctica. In terms of the Lost Meteorite of Antarctica project goals finding this sample is very interesting – as it is a stony-iron type of meteorite would would have perhaps expected to find meteorites like this sitting below the ice, rather than on the top ice surface. We are looking into this question as we classify more of the samples we found!

Description: Taken from the Meteoritical Bulletin for OUT 18018

History: The meteorite was recovered as part of the Lost Meteorites of Antarctica project, which was funded in the UK by the Leverhulme Trust and supported by the British Antarctic Survey and the University of Manchester. These samples were collected as part of the project’s first field season in austral summer December 2018 – January 2019 by a two person field party consisting of Katherine Joy and Julie Baum. Found on blue ice surface at Outer Recovery Icefields ice field 3 (west icefield). Altitude 1411 m.

Physical characteristics: Mass: 153.4 g. Pieces: 1. Dimensions: 7 cm × 5 cm × 4 cm. A blocky, part stone with 85% dark gray fusion crust and dark gray exterior. Orange rust visible.

Petrography: Mineral and lithic clasts, and a network of metal grains up to 1 mm in size. Approximately 30% metal (including minor taenite), 30% pyroxene (including minor Ca-rich pyroxene), 23% plagioclase, 6% silica. Minor iron sulfide and merrillite.

Mineral compositions and geochemistry: All analyses by EPMA. Low-Ca pyroxene Fs30.6±0.5Wo3.3±0.7 (N=10).

Specimens: 151.25 g type specimen (main mass) held at the NHM. Similarity (petrography, mineral chemistry) of this stone with the two stones of OUT 18014 suggests a likely pairing relationship.

Project comments: This sample is likely to be paired (not yet proven via cosmogenics) with the two stones that comprise another find called OUT 18014 found ~1.7 km away on the same icefield. We make a tentative pairing between the stones as they have a very similar texture.

Sample images and videos

OUT 18018 sample in the lab after defrosting. Image: Lost Meteorites of Antarctica / The University of Manchester
OUT 18018 sample in the lab after defrosting. Image: Lost Meteorites of Antarctica / The University of Manchester
OUT 18018 sample that has been sliced up in the lab – you can see the metal-rich components as the shiny phases in this cut face. Image: Lost Meteorites of Antarctica / The University of Manchester
OUT 18018 sample in the field. Image: Lost Meteorites of Antarctica / The University of Manchester
3-D model of OUT 18018 meteorite produced by photogrammetry (Harvey et al., LPSC, 2020). Video: Thomas Harvey / Lost Meteorites of Antarctica / The University of Manchester