Winchcombe CM2 meteorite fall 2021 – first results of systematic LASER Raman Spectroscopy
V.H.Hoffmann1, M. Kaliwoda1,2, M. Junge1,2, W.W. Schmahl1,2
Faculty of Geosciences, Department of Geo- and Environmental Sciences, University of Munich;2
Mineralogical State Collection Munich (MSM-SNSB), Munich, Germany

1

In our (online) poster we will report the first results of detailed studies by 2/3 D digital microscopy and high resolution LASER
Raman Spectroscopy on the Winchcombe CM2 meteorite. This project is part of our ongoing investigations on the mineralogyand phase composition on selected and recent falls of carbonaceous chondrites [1,2 and refs. herein]. Scientific background ofthese studies are preinvestigations and necessary technical/methodological developments in the fore-field of the planed
projects on Hayabusa 2 (asteroid Ryugu) and Osiris Rex (asteroid Bennu) returned materials [3,4].
Introduction
The Winchcombe meteorite fireball and fall from 28th february 2021 was the first reported meteorite fall of a carbonaceouschondrite in the UK [5-10]. The next day after the fireball the first finds were made in the private yard of local people(Wilcock family) followed by a number of further finds in the Winchcombe area (total reported mass about 602gr). Most of thefinds were not influenced by any rains. We obtained fragment(s) of the first find made by the Wilcock family for ourinvestigations.
SamplesFigure 1a: Our sample(s), 3D digital microscopy: fragment(s) of the Wilcock find, heavily brecciated, relicts of chondrules andCAI; (b) Large Olivine particle - near forsterite in composition - in the very fine grained phyllosilicate (serpentine) matrix. (c)Calcite bearing well structured CAI.

Fig 1a.

Fig. 1b.

Fig. 1c.

Methods, techniques
The (surface) morphology and mineralogy of the samples was pre-investigated by digital microscopy followed by detailed andsystematic investigations with LASER Raman Spectroscopy [see 11,12 for details]. All Raman experiments have been
performed without further preparation (only cutting) in order to avoid any unwanted effects (e.g. alterations). The obtained
results should be representative because we did a large number of mappings in different scales on matrix and further
components/clasts. We used the 532 nm LASER, Raman shifts were detected between 50-2500 (4500 for water content) cm -1
with a precision of +/- 1-2 cm-1, and magnifications of 100-1000x (long distance lenses only), and a lateral resolution of 0.1µm. Large maps up to 15x15 points in 2D/3D at high resolution allowed to also detect accessory phases / submicron particles
and inclusions. Acquisition times of 1-3 sec and accumulation numbers of up to 5 have been used which allowed to obtainlarge numbers of Raman spectra in short times within the high resolution mappings, and therefore the results should berepresentative. Si and graphite standards were used for calibration measures, in most cases we applied a 6th degree polynomial
for background subtraction.
Results
The matrix of Winchcombe is dominated by phases of the serpentine mineral group which is a common feature of the CM
chondrites and also of C1-C2 ungrouped CC such as Flensburg, Tarda or Tagish Lake [5]. On many matrix spots and different
clasts the serpentine group member cronstedtite could be detected, generally intimately intergrown with the iron sulfide
tochilinite (TCI).
Summarizing, the following phases and components could be found in our preliminary studies:-Serpentine group members (main matrix component)
Cronstedtite / tochilinite aggregates (CTI)
Troilite, pyrrhotite?
Orthopyroxene (OPX)
Olivine (near forsterite)

-Tephroite – like phase (as in Aguas Zarcas)
Carbon phases (no or poor crystallinity)
CAI, calcite bearing
A significant H2O content, more details elsewhere

We could not find any effects or influence of terrestrial alteration which confirms the high quality of the material. FurtherRaman experiments will focus on the minor / accessory phases, the chondrule components and on CAI. Summarizing, thefound phase composition of our Winchcombe sample reflects the typical composition of a CM2 carbonaceous chondrite, withone exception – the tephroite like phase.
To perform successful LASER Raman spectroscopy experiments on carbonaceous chondrites, (in our recent projects on theMukundpura, Flensburg, Tarda, Kolang, Aguas Zarcas and here Winchcombe meteorite falls) requires the design of a highlysophisticated experimental setup in order to avoid or at least minimize alteration effects already during the measurements on
the one hand and to guarantee a reasonable signal/noise relationship on the other. Therefore we decided to investigate only
naturally broken unprepared sample materials whenever possible. The representativity of the data obtained on the available
sample material was also topic of our studies: large sets of high resolution mappings in 2D/3D can help to overcome theproblem of tiny samples / fragments. Our main interests were on optimizing and fine tuning our experimental setup. So theseries of recent meteorite falls which produced a new set of primitive carbonaceous chondrites provided us directly withunique fresh analogue materials for Hayabusa 2 (Ryugu) and Osiris Rex (Bennu) asteroidal samples in our laboratories.
Figure 2: Representative Raman spectra as obtained on our Winchcombe sample: (a) Olivine particle – near forsterite incomposition and a significant concentration of non-crystalline carbon phases; (b) OPX (chondrule?) and indications for waterin the matrix (Raman shift > 3000 cm -1); (c) Raman spectrum of a tephroite – like olivine group phase which we also could
find for example in Aguas Zarcas (CM2). A tephroite like phase was not reported to our best knowledge from CM meteorites.

Fig. 2a.

Fig. 2b.

Fig. 2c.

References[1] Hoffmann V.H. et al., 2021. 8th ISAS Symp. Solar System Mater. (Hayabusa 2021).
[2] Hoffmann V.H., Kaliwoda M., Junge M., Schmahl W.W., 2022. LPSC conference, iposter, # 2231.
[3] https://www.hayabusa2.jaxa.jp[4] https://www.nasa.gov/osiris-rex.
[5] Meteoritical Bulletin: www.lpi.usra.edu/meteor/metbull Winchcombe, Tarda, Flensburg, Tagish Lake, last visit 10 / 2022.
[6] Daly L., King A.J., Joy K.H., Rowe J., UK Fireball Alliance, 2021. Elements, DOI: 10.2138/gselements.17.5.363.
[7] Simms M.J., 2021. Geology Today, 37, 237-240.
[8] https://karmaka.de/?p=26757: Winchcombe meteorite fall (2022).
[9] Russell S.S., Salge T., King A., Daly L., Joy K., Bates H., Almeida N.V., Suttle M., Schofield P., UK Fireball Alliance
Team, 2022. Microsc. Microanal. 28 (Suppl 1), 2732-2733.
[10] Winchcombe meteorite fall 2021 in: 85th Annual Meeting of the Meteoritical Society 2022, contributions no: 6443, 6408,6356, 6431, 6379, 6345, 6285, 6123, 6076, 6262, 6219.
[11] Hoffmann V.H., et al. 2022a. Inter. Mineral. Congress, iposter # 1477.
[12] Hoffmann V.H., et al. 2022b. Inter. Mineral. Congress, iposter # 1498.