# Nanoscale mineralogy and organic structure in Orgueil (CI) and EET 92042 (CR) carbonaceous chondrites studied with AFM-IR spectroscopy

van T. H. Phan, Rolando Rebois, Pierre Beck, Eric Quirico, Lydie Bonal, Takaaki Noguchi

<figure><img src="image_1.png" /></figure>

► To cite this version:

van T. H. Phan, Rolando Rebois, Pierre Beck, Eric Quirico, Lydie Bonal, et al.. Nanoscale mineralogy and organic structure in Orgueil (CI) and EET 92042 (CR) carbonaceous chondrites studied with AFM-IR spectroscopy. Meteoritics and Planetary Science, 2022, 57, pp.3-21. 10.1111/maps.13773 . insu-03636655

HAL Id: insu-03636655

https://insu.hal.science/insu-03636655v1

Submitted on 20 Aug 2025

**HAL** is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>
# Nanoscale mineralogy and organic structure in Orgueil (CI) and EET 92042 (CR) carbonaceous chondrites studied with AFM-IR spectroscopy

Van T. H. PHAN<sup>ID 1*</sup>, Rolando REBOIS<sup>1</sup>, Pierre BECK<sup>1</sup>, Eric QUIRICO<sup>1</sup>, Lydie BONAL<sup>1</sup>, and Takaaki NOGUCHI<sup>ID 2</sup>

**Abstract**—Meteorite matrices from primitive chondrites are an interplay of ingredients at the sub-µm scale, which requires analytical techniques with the nanometer spatial resolution to decipher the composition of individual components in their petrographic context. Infrared spectroscopy is an effective method that enables the probing of vibrations at the molecule atomic scale of organic and inorganic compounds but is often limited to a few micrometers in spatial resolution. To efficiently distinguish spectral signatures of the different constituents, we apply here nano-infrared spectroscopy (AFM-IR), based on the combination of infrared and atomic force microscopy, having a spatial resolution beyond the diffraction limits. Our study aims to characterize two chosen meteorite samples to investigate primitive material in terms of bulk chemistry (the CI chondrite Orgueil) and organic composition (the CR chondrite EET 92042). We confirm that this technique allows unmixing the IR signatures of organics and minerals to assess the variability of organic structure within these samples. We report an investigation of the impact of the widely used chemical HF/HCl (hydrogen fluoride/hydrochloric acid) extraction on the nature of refractory organics (insoluble organic matter [IOM]) and provide insights on the mineralogy of meteorite matrices from these two samples by comparing to reference (extra)terrestrial materials. These findings are discussed with a perspective toward understanding the impact of post-accretional aqueous alteration and thermal metamorphism on the composition of chondrites. Last, we highlight that the heterogeneity of organic matter within meteoritic materials extends down to the nanoscale, and by comparison with IOMs, oxygenated chemical groups are not affected by acid extractions.

## INTRODUCTION

Extraterrestrial materials are the major source of information on the processes that were at play during the formation of our planetary system. In particular, chondrites, which were accreted within a few million years after the proto-Sun formation, provide key information on processes occurring within the solar protoplanetary disk (evaporation, condensation, transport, organo-synthesis, and so on) as well as information on the geological evolution of the freshly accreted planetesimals (interaction

with water, collisions, radiogenic heating). While chondrules and calcium-aluminum inclusions were formed at elevated temperatures, meteorite matrices are a mixture of components that span formation conditions ranging from high-temperature condensation (e.g., enstatite whiskers) to much lower temperature (e.g., phyllosilicates). Meteorite matrices also host a diversity of organic compounds ranging from small molecules containing only a few carbon atoms to macromolecular refractory organic matter (Alexander et al., 2017; Quirico & Bonal, 2019; Sephton, 2002). Meteorite matrices are thus an interplay of

<footnote n="1"><sup>1</sup>Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Université Grenoble Alpes/CNRS-INSU, UMR 5274, Grenoble F-38041, France</footnote>

<footnote n="2"><sup>2</sup>Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan</footnote>

<footnote>*Corresponding author. E-mail: thi-hai-van.phan@univ-grenoble-alpes.fr</footnote>

<footnote>(Received 28 September 2021; revision accepted 18 November 2021)</footnote>
ingredients at the sub-µm scale, which requires analytical techniques with the sub-µm spatial resolution to unmix their composition and decipher their petrographic relations.

Infrared spectroscopy is a method that enables probing of vibrations at the molecule-atomic scale within gas, liquid, or solid-state samples. Of major interest in planetary sciences is the fact that the strong dipole moment of –OH leads to the presence of strong infrared (IR) absorptions, which have been used to identify water or hydrated minerals in planets, meteorites, and asteroids. The various types of silicates can also be studied with infrared spectroscopy given the presence of $SiO_4^{4-}$ bending and stretching absorptions, which provides information on the silicate framework and permits identification of specific mineral phase as well as amorphous silicates (Beck et al., 2014; Crovisier et al., 1997). Infrared spectroscopy is also a method that is used intensively to study the structure of carbonaceous compounds since the carbon framework can be investigated through the identification of chemical groups (e.g., C=C, C-C, C-H bonds), as well as the nature and bonding environment of heteroatoms (O, N, S) (Orthous-Daunay et al., 2013; Phan et al., 2021).

There are, however, two major challenges with the application of IR spectroscopy to natural samples. First, to be quantitative, spectra are often acquired in transmission mode, which requires an appropriate preparation for the sample to be optically thin. But given that IR absorption strengths are variable among the species of interest, the optimum thickness may depend on the chemical compound being investigated. Second, conventional IR spectrometers use mirror-based optics to focus the beam toward the samples, and the spatial resolution is intrinsically limited by diffraction. This means that the typical spatial resolution of 5–10 µm is often studied in the mid-infrared, and in the case of chondritic matrices, the different components will be mixed within the analyzed area. This generates major difficulties in interpreting the obtained spectra since spectral congestion will occur between silicate and organically related absorptions. One possibility to circumvent this issue in the case of organic compounds is to use chemical extraction and to perform IR spectroscopy on the extracted organics. This has been done and revealed for instance chemical variabilities between insoluble organic matter (IOM) of different carbonaceous chondrites (Alexander et al., 2007, 2010; Cody & Alexander, 2005; Orthous-Daunay et al., 2013; Quirico et al., 2014, 2018). In that case, however, information on the possibility of heterogeneities of organics within a sample is lost, as well as the petrographic relation with other constituents (silicates, metals, and so on). Also, harsh chemical extraction may have an impact on the oxygenated groups of organic matter (Painter et al., 1981; Petersen et al., 2008).

The recent development of nanoscale IR spectroscopy offers some exciting perspectives in the field of earth science in general, and in the case of meteoritic studies, the possibility to circumvent the aforementioned issues. This method is based on the coupling between atomic force microscopy and IR laser sources, which provides an opportunity to break the diffraction limit (Dazzi et al., 2005, 2012). This technique has been already applied to extraterrestrial samples (Kebukawa et al., 2018; Mathurin et al., 2019; Yesiltas et al., 2021). Here, we present results obtained using atomic force microscope-infrared (AFM-IR) spectroscopy on two raw matrix meteorite samples, compared to those obtained on IOM extracted by hydrogen fluoride/hydrochloric acid (HF/HCl) digestion. They were chosen to investigate primitive material in terms of bulk chemistry (the CI chondrite Orgueil) and organic composition (the CR chondrite Elephant Moraine [EET] 92042—the weathering grade B). Our objectives with this work are:

i. Assess the performance of the AFM-IR technique for natural samples by looking at reference terrestrial and extraterrestrial materials.

ii. Unmix the IR signatures of organics and minerals to assess the variability of organic structure within these samples.

iii. Assess the impact of the widely used chemical extraction on the nature of refractory organics.

iv. Provide insights into the mineralogy of meteorite matrices from these two samples with AFM-IR.

# MATERIALS AND METHODS

## Sample Set

We selected two meteorites including the EET 92042 CR chondrite, the Orgueil CI chondrite, as well as their extracted IOM. The Orgueil (CI) chondrite was chosen because of its primitive bulk chemical composition (Tomeoka & Buseck, 1988; Tomeoka et al., 1989), whereas the EET 92042 sample was selected given its expected pristine nature based on its petrology (e.g., Brearley, 2006). The bulk meteorites were prepared through two different methods: Focus ion beam milling and sulfur embedding ultramicrotomy, which will be described in the following section. The IOM samples of EET 92042 and Orgueil were extracted by demineralization with HF/HCl acid attacks to remove sulfates, carbonates, silicates, and neoformed fluoride (Amari et al., 1994; Gardinier et al., 2000) following the continual flux method described in Orthous-Daunay et al. (2010).

A series of nine natural minerals were also used for the interpretation of mineralogy in carbonaceous chondrites including saponite, dolomite, kaolinite,
<table><caption>Table 1. Studied samples and summary of different sample preparations used for conventional Fourier-transform infrared (FTIR) spectroscopy, micro-FTIR, and AFM-IR analysis (more details described in following sections)</caption><thead><tr><th rowspan="2">Type</th><th rowspan="2">Name</th><th rowspan="2">Chemical preparation</th><th colspan="3">Sample preparation</th><th rowspan="2">Reference</th></tr><tr><th>KBr-pellet FTIR</th><th>μ-FTIR</th><th>AFM-IR</th></tr></thead><tbody><tr><td>Pure minerals</td><td>Dolomite<br>Kaolinite<br>Saponite<br>Gypsum<br>Smectite<br>Calcite<br>Dunite<br>Antigorite<br>Amorphous silicate</td><td>Fresh minerals</td><td>Pressed<br>mixture pellet</td><td></td><td></td><td></td></tr><tr><td>Meteorites</td><td>EET 92042</td><td>"Bulk" meteorites</td><td></td><td></td><td>Focus ion<br>beam milling</td><td>Noguchi<br>et al. (2020)</td></tr><tr><td></td><td>Orgueil</td><td></td><td></td><td>orgueil</td><td>Sulfur-embedding<br>ultramicrotomy</td><td></td></tr><tr><td>IOM</td><td>EET 92042<br>Orgueil</td><td>Demineralization<br>with HF/HCl</td><td>orgueil</td><td></td><td>orgueil</td><td>Orthous-Daunay<br>et al. (2010)</td></tr></tbody></table>

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

gypsum, smectite, calcite, amorphous silicate, olivine, and antigorite (Table 1). All minerals were provided by the collection of the Observatoire des Sciences de la l'univers de Grenoble. Those are natural samples and may contain some impurities (e.g., Cr in olivine), but they are more suitable for the meteoritic intrinsic complexity.

## Sample Preparation

The samples were prepared in different ways to be optimized for the AFM-IR and FTIR analyses following Table 1.

### Focused Ion Beam Milling

A dual column focused ion beam (FIB) using a Ga field emission gun and a scanning electron microscope (FEG-SEM) Carl ZEISS NVISION 40 system were used at Commissariat à l'Énergie atomique and Consortium des Moyens Technologiques Communs (CEA/CMTC, Grenoble, France). First, platinum strips (~20 [long] × 2 [wide] × 5 [thick] µm) were deposited on the samples to minimize ion beam damage during the sample sectioning. Approximately 2 µm thick sections were prepared for AFM-IR analysis. During the initial extraction from a bulk

sample, ion beam milling was processed at a Ga⁺ ion beam voltage of 30 kV and beam currents ranging from 1 to 3 nA. A thin section ~2 µm thickness was lifted out using an MM3A-EM micromanipulator (Kleindiek Nanotechnik) and was transferred to a Cu transmission electron microscope (TEM) half grid for final ion polishing. Ion currents in the range of 30–300 pA were used to achieve a thickness of about ~1 µm. An FIB section 20 (wide) × 25 (long) × 1.5 (thick) µm was attached with the Cu grid. To perform AFM-IR analysis, the FIB–Cu grid was deposited on ZnS substrate and under the microscope, we separated the FIB section from Cu grid using a Tungsten needle (Fig. S1 in the supporting information).

### Sulfur-Embedding Ultramicrotome

The fragment of Orgueil chondrite was prepared using ultramicrotomy after sulfur embedding at Kyushu University (Fukuoka, Japan), following a procedure optimized and developed by Noguchi et al. (2020). Ultrapure sulfur powder (S₈; 99.998%, Sigma-Aldrich) was put down to a stainless steel stub located at a heated plate and heated to 170–180 °C. We checked the quality of this sulfur droplet through its transparence, before inserting the Orgueil grain into it. The detailed
procedure was checked under the microscope before setting into the ultramicrotome as described in Noguchi et al. (2020). Before slicing sample sections, the sulfur droplet was cut in four edges using a DIATOME diamond knife trim 45°. The meteoritic fragment was sliced into ~90–100 nm ultrathin sections with a Leica ultramicrotome using a DIATOME ultra 35° diamond knife. After cutting, the released sections were deposited at the surface of deionized ultrapure water, filled on the curve of the diamond knife, and then transferred to a ZnS substrate. Before AFM-IR measurement, sections were slightly heated at 70–80 °C in the oven overnight to expel sulfur.

## Pressed and Kbr Pellet Preparation

For µ-FTIR analysis, the fragments of IOM/meteorites/minerals (~50 µm × 50 µm) were pressed between two diamond windows (type IIa diamond, 3 mm diameter, 500 µm thick) to obtain thin and flat samples (1–5 µm thick). The upper window was removed to avoid interference during the measurements in transmission mode. This sample preparation strongly reduces scattering artifacts and is well suited for spectral imaging. The pressed samples were not only used for µ-FTIR but also for optimization of the measurement's conditions of AFM-IR analysis (e.g., power, thickness), allowing to maximize the signal-to-noise ratio (SNR) of AFM-IR spectra.

For the FTIR measurements of nine reference minerals (Table 1), mineral powders (0.2 ± 0.02 mg) were ground and mixed with 300 mg KBr with an MM200 Retsch grinder equipped with an agate mortar filled with a single ball (30 Hz, 30 min). Then, 13 mm diameter pellets were prepared using a press Atlas™ Manuelles (Eurolabo), under 400 bars pressure and mild heating (60 °C), then cooled down for 30 min.

For the AFM-IR analysis of pure minerals, 13 mm double-layer pellets were prepared using a first 700 mg of KBr pellet topped with 100 mg of minerals and then pressed again. The pressure was applied under pumping and gentle heating to minimize moisture in the hygroscopic KBr.

## Conventional FTIR Spectroscopy

The FTIR instrument used in this study is a Bruker Hyperion3000. The beam is modulated in an interferometer and the intensity is collected by a liquid nitrogen-cooled-mercury cadmium telluride (MCT) detector. The spectral range was 4000–400 cm⁻¹ with a spectral resolution of 4 cm⁻¹ and 200 scans to get satisfying SNR. All measurements were done using a cell connected to a turbomolecular pump assisted with a membrane primary pump, with an optical path through

two ZnS windows (Beck et al., 2010). The loaded diamond window was maintained to a secondary vacuum (typically ~10⁻⁶ mbar) and slightly heated to 80 °C to remove weakly bonded water from the sample. Background measurements were performed from an area next to the sample to monitor window cleanliness and reference baselines were acquired immediately before each sample measurement.

## AFM-IR Spectroscopy and Imaging

The IR absorption spectra and maps were collected using a NanoIR3s™ (Brucker) at the Institut de Planétologie et d'Astrophysique (IPAG, Grenoble, France), which includes an AFM that can scan the sample and generates topographic images at nm vertical resolution. In addition, the nanoIR3s consists of two pulsed and tunable IR sources to excite infrared absorption in a sample (Bruker, 2019). As the sample heats up by absorbing radiation, the local rapid thermal expansion afterward is detected by an AFM probe. The fast expansion leads the AFM cantilever to oscillate at its contact resonant oscillations (Dazzi & Prater, 2017). The amplitude of the generated oscillations is a proxy of the absorption of the sample at the excitation wavelength, and is similar to the standard transmission spectrum collected by conventional FTIR. As a consequence, the spatial resolution is not limited by the diffraction limit as conventional IR microscopes and spectra can be located with a spatial scale <100 nm (Dazzi & Prater, 2017).

The IPAG NanoIR3s platform is equipped with two laser sources: a Firefly laser in the range 2000–3600 cm⁻¹ wave number and an APE Mid-IR laser Carmina in the range 600–2000 cm⁻¹ wave number. The APE laser sets new standards in resolution and tuning range due to its optical parametric oscillator/difference frequency generation architecture with four configurations and a power higher than 10 mW at 1600 cm⁻¹. The system can perform different AFM-IR analysis modes including tapping, contact mode, and tapping AFM-IR mode. The tapping AFM-IR is based on principles from multifrequency AFM in which combined flexural eigenmodes of the AFM cantilever are excited to enhance the sensitivity of the probe-sample interaction (Mathurin et al., 2018). As a consequence, the highest signal-to-noise performance is obtained during the movement of cantilever oscillations (Dazzi et al., 2012; Mathurin et al., 2018). Each spectrum was obtained at selected points with a wave number spacing of 4 cm⁻¹ using both contact and tapping modes. The incident laser powers were set to 2–11% in the range 900–2000 cm⁻¹ wave number and 1–5% in the range 2000–3600 cm⁻¹. The IR
spectra were optimized to a constant laser power level at each wave number with the laser power detected by an IR-sensitive photodetector.

For the IR maps, the laser power was set to 25–80% in the range of 900–2000 cm⁻¹ with the tapping AFM-IR mode to avoid mechanical damage from the probe at the sample surface. All AFM scans in the AFM-IR mode were done using a semi-tapping gold-coated cantilever model PR-EX-TnIR-A-10 (resonance frequency: 75 ± 15 kHz, spring constant: 1–7 N m⁻¹) which allows working with both on contact and tapping AFM-IR modes.

## RESULTS

### AFM-IR of Pure Reference Minerals

The fundamental vibrational modes of nine minerals including dolomite, kaolinite, gypsum, saponite, smectite, calcite, antigorite, amorphous silicate, and olivine in dunite were displayed in mid-IR spectra, from both µ-FTIR and KBr pellet FTIR analyses (Fig. S2 in the supporting information). The AFM-IR spectra of calcite and antigorite were collected only using the Firefly laser in the range from 2000 to 3800 cm⁻¹, whereas the amorphous silicate and olivine in dunite were only measured in the range 700–2000 cm⁻¹ using the APE laser (Fig. S2).

Dolomite and calcite (Ca-carbonate) often occur with a significant amount in CI chondrites (Tomeoka & Buseck, 1988; Tomeoka et al., 1989). AFM-IR single-point spectra in the 3 µm region reveal bands at 3006 and 2890 cm⁻¹ in dolomite, and 2974 and 2870 cm⁻¹ in calcite, corresponding to the antisymmetric and symmetric stretch vibration modes of the carbonate ion, respectively, consistently with the µ-FTIR and KBr-pellet spectra (Fig. S2). Note that KBr-pellet spectra show the presence of H₂O and an organic contaminant present in the organic matter in the KBr powder (Figs. S2a and S2c). The dolomite AFM-IR spectra also show the fundamental carbonate bands at 1806 cm⁻¹ (v₁), ~1450 cm⁻¹ (v₃), 880 cm⁻¹ (v₂), and 730 cm⁻¹ (v₄), with positions similar to those in conventional FTIR spectra. The AFM-IR spectra of kaolinite display features between 3600 and 3700 cm⁻¹ corresponding to the stretching vibration of –OH groups which are very similar to those in FTIR spectra (Fig. S2b). The bands of 3695 and 3620 cm⁻¹ derived from AFM-IR spectra are lightly broader but similar to the FTIR ones corresponding to the –OH stretching modes. The features at 1110, 1040, and 920 cm⁻¹ are due to Si-O stretching, bending modes, and –OH deformation mode in Al-OH of kaolinite structure. Overall, the AFM-IR kaolinite spectra look very similar to FTIR spectra except for the broader and weaker feature at 1110 cm⁻¹.

Saponite is often interlayered with serpentine (e.g., chrysotile, lizardite, and antigorite), one of the important products in the alteration of the CI, CM, and CR chondrites (Glavin et al., 2018). As seen in Figs. S2c and S2h, the AFM-IR spectra of saponite and antigorite heated at 500 °C collected in the range 3800–2700 cm⁻¹, show the features at 3670 and 3690 cm⁻¹, respectively, which correspond to the OH stretching vibration. In particular, antigorite AFM-IR spectra are fully consistent with µ-FTIR spectra, whereas, for saponite, a higher intensity of the 3670 cm⁻¹ features is observed. In the case of the amorphous silicate and olivine in dunite, spectra were only measured in the 2000–700 cm⁻¹ range. The main bands in olivine spectra are observed at 990, 890, and 840 cm⁻¹ and are assigned to Si-O stretching modes. In contrast, the AFM-IR spectra of the amorphous silicate show an Si-O band with three main peaks at 1420, 1180, and 980 cm⁻¹, while a unique and broad band at 1000 cm⁻¹ due to Si-O stretching modes was observed for both KBr-pellet and µ-FTIR. The reason for this discrepancy is being investigated.

Gypsum (CaSO₄) or the other forms of Ca-sulfate was also found in some meteorites where it was intimately associated with CaCO₃ such as EETA 79001 (Gooding et al., 1988). In comparison to KBr-pellet and µ-FTIR spectra in Fig. S2d, AFM-IR spectra of gypsum reveal the presence of the stretching vibration mode of OH bond at 3600 cm⁻¹, and a broader peak at 3400 cm⁻¹ slightly different from the mid-IR spectra centered at 3550 and 3400 cm⁻¹, respectively. The two deformation vibration bands of the OH groups at 1675 and 1621 cm⁻¹ are similar in AFM-IR and FTIR spectra. In contrast, the typical vibration bands of sulfate centered at 1110 and 1200 cm⁻¹ in AFM-IR spectra are different than those in FTIR spectra. One possible explanation is that upon exposure to dry air, the sulfate was dedicated to leading to some changes in the crystallographic structure.

### Nanoscale IR Spectra of IOM

In the following paragraphs, we present the AFM-IR spectra and maps obtained on IOM extracted from the two meteorite samples.

#### EET 92042 (CR) IOM

The IR absorption images of IOM extracted from EET 92042 were recorded with the IR source tuned to 1720, 1600, 1450, and 1040 cm⁻¹ corresponding to carbonyl (C=O), aromatic (C=C), aliphatic (CH₂ bending), and silicate groups (Si-O stretching), respectively (Figs. 1a–e). For each map, the height topography was recorded to monitor for the thermal
drift during the experiment. The IR maps are shown in Fig. 1 and reveal variability in the AFM-IR intensity over the analyzed area. The comparison to the topographic map reveals that some of the trends are related to sample height: For instance, the area with fractures or the topographic low height around points S2–S3 shows overall a lower AFM-IR intensity. The contact resonance frequency is likely different in these areas, which leads to a lower AFM-IR signal (the pulse repetition rate is optimized only once before a chemical map is obtained), as well as to the fact that variable thickness can lead to variation in magnitude of the laser-induced thermal expansion. Overall, this map reveals the presence of correlated organic matter absorption at 1720, 1600, and 1450 cm⁻¹ and negligible signatures of silicate minerals that would produce absorptions around 1000 cm⁻¹ (Si-O stretching modes). These maps suggest that the IOM is quite homogeneous and that minerals were efficiently removed by the chemical extraction. It also emphasizes the general need to work with smooth and flat surfaces for AFM-IR measurements (with a typical standard deviation of the topography below 50 nm).

The functional C groups present in the IOM of EET 92042 were reported in previous studies based on µ-FTIR (Kebukawa et al., 2011; Orthous-Daunay et al., 2013). The µ-FTIR spectrum of Fig. 1g (in blue) is similar to the IOM AFM-IR spectra with the absorption band peaking at 1700 and 1600 cm⁻¹ attributed to C=O and C=C and the I₁₇₀₀/I₁₆₀₀ ratio of 0.9. A line of AFM-IR single-point spectra (marked in Figs. 1a and 1b) was collected. Spectra of S1, S2, and S3 represent a spectral blank that corresponds to the ZnS substrate. The shape of the other AFM-IR spectra (e.g., S4–S25) is quite similar to typical IOM. To compare with µ-FTIR spectra, the average spectrum, shown in Fig. 1g, based on around 100 single-point spectra suggesting that the I₁₇₂₀/I₁₆₀₀ is around 0.9–1.1, which is slightly higher than the one derived from FTIR proxy (0.9).

### Orgueil (CI) IOM

The AFM-IR maps of the IOM extracted from Orgueil are shown in Fig. 2. Infrared maps were recorded at the same laser wave numbers as for the IOM of EET 92042. Again, we see a strong correlation between IR maps obtained at 1720, 1600, and 1450 cm⁻¹ (Figs. 2b and 2c). In contrast to the IOM of EET 92042, the IOM of Orgueil is not homogeneous, with an area showing a significant absorption at 1000 cm⁻¹ that may result from the uncompleted mineral removal through the chemical extraction or from the presence of residual SiF₄ crystals. This

absorption is not observed on µ-FTIR spectra, but this difference may be attributed to heterogeneity in the distribution of these mineral residues within the IOM (Fig. 2f).

The point AFM-IR spectra, obtained outside of the area with the strong 1000 cm⁻¹ signal in IR maps, reveal the presence of bands at 1700 and 1600 cm⁻¹ assigned to C=O and C=C, respectively, as well as at 1450 cm⁻¹ attributed to CH₂ (Fig. 2g). Spectra obtained in the area with the strong 1000 cm⁻¹ signal in IR maps display additional signatures around 1250 and 1000 cm⁻¹ that are tentatively assigned to a mineral phase and/or SiF₄ crystal which may remain and/or form from the chemical extraction using HF.

### Nanoscale IR Spectra of Raw Carbonaceous Chondrites

#### EET 92042 CR Chondrite

An area of an FIB section of EET 92042 was mapped with the Tapping AFM-IR mode (5 × 5 µm²). Results are shown in Fig. 3. The AFM-IR images at different wavelengths were obtained at 1720, 1600, 1450, and 1000 cm⁻¹ corresponding to C=O, polyaromatic C=C, carbonate (CO₃), and Si-O stretching, respectively (Figs. 3b–e). These maps and the generated composite RGB images enabled the identification of three different types of domains in the mapped area (Fig. 3f). The first region is located at the bottom left of the images and can be distinguished by a strong absorption at 1450 cm⁻¹ and attributed to the presence of carbonate. The second region is in the form of a vein (red in the RGB image Fig. 3f) that has stronger absorption related to organics (1720 and 1600 cm⁻¹). The last region corresponds to the rest of the image, where the most intense signal detected can be attributed to silicates (1000 cm⁻¹).

Several AFM-IR spectra were obtained across this FIB section (Fig. 3g). These spectra reveal the strength of AFM-IR spectroscopy to unmix spectral signatures at a sub-µm scale since such an area (5 × 5 µm²) would correspond to only one pixel using conventional micro-FTIR. The spectra obtained in the center of the carbonate grain (P19) show signatures at 1460 and 870 cm⁻¹ together with a faint feature around 1800 cm⁻¹ all suggestive of carbonate. Spectra obtained in the green area of the RGB map reveal the presence of a broad and variable feature around 1000 cm⁻¹ that is attributed to phyllosilicates whose nature will be discussed in the Silicate Mineralogy section. In the case of the red vein in the RGB maps, organic signatures at 1720 and 1600 cm⁻¹ are visible in the point spectra. This organic-rich area is finely mixed with phyllosilicate given the presence of associated silicate bands.
<figure><img src="image_9.png" /><figcaption>Fig. 1. IOM extracted from EET 92042 (CR2 chondrites; 10 × 10 µm²). IR map for each wave number with corresponding (a) AFM image at (b) 1720 cm⁻¹, (c) 1600 cm⁻¹, (d) 1450 cm⁻¹, and (e) 1000 cm⁻¹; (f) AFM-IR single-point spectra (scaled) for the region of 2000–700 cm⁻¹ (labeled S1 to S25 with a line of 25 spectra) performed in selected locations shown on the AFM and 1720 cm⁻¹ image; (g) comparison between the AFM-IR average spectra derived from 100 spectra (with the standard deviation gray bar) and µ-FTIR spectra. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Fig. 2. IOM extracted from Orgueil (CI chondrite; 10 × 10 µm²). IR map for each wave number with corresponding (a) AFM image at (b) 1720 cm⁻¹, (c) 1600 cm⁻¹, (d) 1450 cm⁻¹, (e) 1380 cm⁻¹, and (f) 1000 cm⁻¹. g) Comparison of AFM-IR average spectra and µ-FTIR spectra including the 40 average (red) and five average (purple) spectra, including to the standard deviation bar in the position without and with the signature of 1000 cm⁻¹, respectively, in the range of 2000–700 cm⁻¹ performed in selected locations shown on the AFM and 1000 cm⁻¹ image. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>Fig. 3. EET 92042 (5 × 5µm²). AFMIR maps recorded from (a) topographical image, at (b) C = O at 1720 cm⁻¹, (c) C = C and -OH stretch at 1600 cm⁻¹, (d) CO3 at 1450 cm⁻¹, (e) silicates Si-O at 1000 cm⁻¹, and (f) a composite (red, green, blue) image of the three maps: 1720, 1000, and 1450 cm⁻¹, respectively. g) AFM-IR single-point spectra in the 2000–700 cm⁻¹ range (labeled L1–L20 with a line of 20 spectra and P1–P20 with point by point spectra) were performed in selected locations shown on the AFM and RGB composite images (a, f). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

### Orgueil CI Chondrite

IR absorption maps of a microtome section of Orgueil were obtained over an area of 4 × 4 µm², at 1720, 1450,

1150, and 1040 cm⁻¹, respectively (Figs. 4a–e). The AFM-IR RGB composite map shown in Fig. 4f is an overlay of the three channels of 1710, 1450, and 1000 cm⁻¹.
These maps reveal the nanoscale heterogeneity of the mineralogy and organic distribution in Orgueil, for which three spectral endmembers were identified based on point measurement. The first endmember is phyllosilicate, with a peak around $1000 \text{ cm}^{-1}$ (e.g., point O14, Fig. 4), which is thinner than the silicate absorption in EET 92042 (CR). The second endmember shows a triplet at 1150, 1090, and $980 \text{ cm}^{-1}$ as well as a doublet at 1465 and $1425 \text{ cm}^{-1}$ (e.g., point O01). This endmember is interpreted by the presence of a hydrated sulfate. The last endmember is attributed to organic compounds. It seems to be present diffusively in the sample except for a few areas like point O19, which shows a stronger signature around $1700 \text{ cm}^{-1}$ than the rest of the sample (Fig. 4). More spectra of organic matter were observed in the section nearby the one in Fig. 4 (e.g., S10, S13, S14, and S15 in Fig. S3 in the supporting information), which show clearly the signature of carbonyl and polyaromatic around $1700 \text{ and } 1600 \text{ cm}^{-1}$, respectively.

## DISCUSSION

### Organic Signatures and Structure, and the Effect of Acid Extraction

Figure 1g displays a conventional µ-FTIR spectrum of the IOM sample of EET 92042 and an AFM-IR average spectrum. The bands at 1720 (C=O) and $1600 \text{ cm}^{-1}$ (aromatic) are observed in both spectra, but the intensity of the C=O band is systematically higher than that of the aromatic band in the AFM-IR spectrum. In the AFM-IR average spectrum, the baseline (zero-absorption continuum) is not located on the side of high wave number: This is particularly visible at the edge of the $1720 \text{ cm}^{-1}$ band and the range $1500-900 \text{ cm}^{-1}$ is noisy. The AFM-IR average spectrum does not display the $CH_2$ and $CH_3$ bending modes (1450 and $1380 \text{ cm}^{-1}$), nor the broad congested bands at ~1250 $\text{cm}^{-1}$ (C-O, C-C, OH, etc.) that systematically appear in conventional µ-FTIR spectra, from this study and in published data (Kebukawa et al., 2011; Orthous-Daunay et al., 2013). Similar observations are achieved in spectra of Orgueil IOM regarding the ratio of the 1720 and $1600 \text{ cm}^{-1}$ bands (Fig. 2). However, AFM-IR and µ-FTIR spectra look more similar in the range $1500-900 \text{ cm}^{-1}$. The $CH_2$ and $CH_3$ bending bands are present, and the broad congested band looks more similar as well, except for two bumps at 1240 and $1000 \text{ cm}^{-1}$. These bumps could be assigned to aromatic-ethers aromatic-O-$CH_2$ and C-O bonds, respectively, and their spatial variations may point to chemical heterogeneity of Orgueil-IOM.

These spectral differences between conventional µ-FTIR and AFM-IR spectra are not due to instrumental

artifacts, as we collected AFM-IR spectra of simple polymer films (e.g., polybutadiene) similar to µ-FTIR spectra (Fig. S4 in the supporting information). They point to the extreme sensitivity of the technique to the nature of the sample and its preparation. Natural samples are heterogeneous and porous at the nm scale, resulting in complex heat transfer. Therefore, the volumetric expansion triggered by the laser could not be controlled by the sole absorption properties of the organic material. The sample preparation also plays a key role, and spectra can depend on thickness and compaction (if it is prepared by crushing). In this respect, the interpretation of AFM-IR spectra of natural materials needs to be based on AFM-IR spectra obtained on reference samples, if possible prepared with similar sample preparation.

AFM-IR measurements on raw matrix samples of EET 92042 display the signatures of minerals and organics. The $1700-1600 \text{ cm}^{-1}$ spectral region is possibly contaminated by the bending mode of molecular water. Selecting spectra with a low Si-O band minimizes this spectral contamination and reveals the actual signatures of organic matter (Fig. 5). We observe two bands at 1720 and $1600 \text{ cm}^{-1}$, with spatial variability of their relative intensities. In the CR chondrite Renazzo, organic matter is mostly present as grains of a few hundreds of nm that are not intermixed with hydrated minerals (Le Guillou et al., 2014). In the very primitive CR MET 00426, organic matter is present as individual particles over a broader range of a size (from a few nm to several µm), but the main population is around 100–500 nm in size, which is larger than the spatial resolution achieved with AFM-IR (Le Guillou et al., 2014). A diffuse organic matter is also reported, showing a higher abundance of –COOH groups and pointing to the presence of soluble organic matter (Sephton, 2002). These observations have been extended to other weakly altered CR chondrites, including EET 92042 (Changela et al., 2018). Our results show no major enhancement of the C=O band, and in this respect, IOM appears as the main organic form in the probed area with little or negligible contribution from soluble organic matter. Our spectra arise from the excitation of rather large IOM grains; nevertheless, we could measure a pure organic area. Last, the presence of fairly separated features at 1720 and $1600 \text{ cm}^{-1}$ in spectra obtained on raw matrix, similar to those in IOM spectra, shows that the HF/HCl acid extraction protocol has little effect on the carbonyl oxygenated groups. These groups are known to be very sensitive to acids, and in demineralized coals, they are harshly modified (Painter et al., 1981; Petersen et al., 2008). IOM samples extracted from
<figure><img src="image_12.png" /><figcaption>Fig. 4. Orgueil—CI Chondrite. (4 × 4 µm²). AFM height (a) and AFM-IR images recorded (b) at 1720 cm⁻¹, (c) at 1450 cm⁻¹, (d) at 1150 cm⁻¹, (e) at 1000 cm⁻¹, and (f) RGB composite (red, green, blue) image of the three maps: 1720, 1000, and 1450 cm⁻¹, respectively. g) AFM-IR single-point spectra in the 2000–700 cm⁻¹ range (labeled O1–O20 for point by point spectra) were performed in selected locations shown on the AFM and RGB composite images (a, f). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
<figure><img src="image_13.png" /><figcaption>Fig. 5. Comparison between infrared spectra of chemically extracted IOM and single-point AFM-IR spectra of organic matter from bulk meteorites (a) Orgueil and (b) EET 92042. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

chondrites by acid digestion are then well chemically representative of the actual refractory organic matter in the bulk chondrite.

In the case of Orgueil, spectra displaying organic features are scarcer than in EET 92042. This may be because organic matter is present in a more diffuse form, with tight intermixing with phyllosilicates (Pearson et al., 2002; Le Guillou et al., 2014). The few spectra displaying a low silicate band reveal, however, two distinct bands at 1720 and 1600 cm⁻¹. The C=O band is more intense and shifted in comparison to Orgueil IOM, suggesting a contribution of soluble organic matter in the spectra obtained on the matrix. Note, however, that only a small number of AFM-IR spectra displaying exploitable organic features derived from organic matter could be collected.

## Silicate Mineralogy

### Phyllosilicates in Orgueil

Unlike most carbonaceous chondrites for which chondrules or chondrule relicts are abundant, the mineralogy of Orgueil and CI chondrites is dominated by a fine-grained, dark, matrix (Tomeoka & Buseck, 1988). The mineralogy of the Orgueil matrix has been investigated using a variety of techniques (X-ray diffraction, Mossbauer, thermogravimetric analysis, etc.), as well as in situ techniques using a combination of SEM and TEM. In the seminal work of Tomeoka and Buseck (1988), it was shown that the matrix of Orgueil is dominated by phyllosilicates, in the form of small grains (<1 µm) and larger aggregates. The mineralogy of these phyllosilicates was found to be
<figure><img src="image_14.png" /><figcaption>Fig. 6. Comparison between pure minerals and single-point AFM-IR spectra from bulk meteorites (a) Orgueil sulfur-embedded ultramicrotomy section, (b) EET 92042 FIB section. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

dominated by mixtures of serpentine and smectite (saponite) as evidenced by the alteration of domains with 7 and 10 Å spacing. This mineralogy is consistent with bulk X-ray diffraction patterns (King et al., 2015). IR spectra of Orgueil obtained on bulk samples using FTIR have been reported previously (Beck et al., 2014; Sandford, 1986). These measurements revealed the presence of an absorption band centered around 10 µm together with smaller features around 1100 and 1150 cm⁻¹, that were previously attributed to sulfates (Beck et al., 2014; Sandford, 1986).

Here, for the first time, we can unmix the spectral signature of the phyllosilicate from that of other matrix constituents (Figs. 4f and 6a). Using AFM-IR spectroscopy, we are therefore able to obtain the “pure” signature of Orgueil phyllosilicate. This reveals a single and relatively narrow peak when compared to CM chondrites (REF) with a maximum of around 9.9 µm. Also apparent

in the spectrum are signatures around 1710 and 1460 cm⁻¹ (e.g., AFM-IR spectra O19) that can be attributed to organic matter finely mixed with the phyllosilicate (Fig. 4f). It is not possible to tell if the organic matter is present within the interlayer space of the phyllosilicate.

The shape and position of the phyllosilicate feature in Orgueil (Fig. 6a) are somehow similar to saponite, but the spectra obtained at a longer wavelength with FTIR in our previous work are not identical to saponite (Beck et al., 2014). We also note that the water bending mode at 1630 cm⁻¹ is not identified in the spectra, while it can be seen in the saponite standard measured with AFM-IR. This suggests that the interlayer spaces of the saponite-like domains in our Orgueil sample are not populated by water molecules. A possibility is that the layers have collapsed (measurements are obtained under dry air) or that the interlayer space is populated with other species (i.e., organics; Pearson et al., 2002).
<figure><img src="image_15.png" /><figcaption>Fig. 7. a) FTIR spectra of the Orgueil CI chondrite and from a typical CM chondrite (Beck et al., 2014) compared to AFM-IR spectra (this study). b) Comparison of the signature observed in the fine-grained matrix of Orgueil to FTIR spectra of selected sulfate (Fe-rich hydrated: copiapite and coquimbite, and Mg-rich hydrated: epsomite). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

Hydrated Amorphous Silicates in the CR Chondrite EET 92042

CR chondrites are usually described as among the most primitive carbonaceous chondrites. This is justified by particularly heavy nitrogen isotopic compositions, the high abundance of presolar grains, and the overall low level of aqueous alteration compared to CM chondrites (Alexander et al., 2007; Bonal et al., 2013). Also, the mineralogy of the matrices of some CR chondrites, as studied by TEM, reveals the presence of abundant amorphous material that would not survive a significant amount of thermal processing (Abreu & Brearley, 2010; Changela et al., 2018; Le Guillou et al., 2015). This amorphous material is intermixed with sulfides, organic material, and tochilinite (Changela et al., 2018).

In Figures 6b (also see Fig. 8a), some spectral endmembers derived from AFM-IR measurements on the CR EET 92042 are shown. Some silicate-dominated regions are present, and different silicate signatures were found (blue spectra in Fig. 6b, green spectra in Fig. 8).

The dominant silicate signature is a broad feature centered around 10 µm, with a width significantly broader than that of Orgueil phyllosilicate (see the Orgueil only Si-O spectrum in Fig. 6a). The position and overall aspect of the peak are consistent with FTIR spectra obtained on matrix grains of the same samples (Bonal et al., 2013). Again, comparison to FTIR data reveals the strength of AFM-IR to unmix the spectral signature in carbonaceous chondrites (see Fig. 8a). The overall shape of these spectra is consistent with an amorphous silicate phase. Interestingly, this spectrum reveals the presence of a feature around 1630 cm⁻¹ (see Fig. 8b), which is the first direct evidence for the presence of water molecules within amorphous silicate from a CR chondrite (Beck et al., 2010).

It has been proposed that the hydration observed in amorphous silicates from CR chondrites could be related to the reaction between amorphous silicates and water (Le Guillou et al., 2015). The obtained AFM-IR spectra of EET 92042 amorphous silicate are remarkably similar to experimental products obtained
<figure><img src="image_16.png" /><figcaption>Fig. 8. a) Selected AFM-IR spectra obtained on EET 92042 compared to FTIR measurements from Bonal et al. (2013) on the same meteorite, and transmission spectra of reference carbonates (FTIR). b) AFM-IR spectra of hydrated amorphous silicates in EET 92042 compared to FTIR spectra of matrix grains (Bonal et al., 2013), Orgueil absorbed water (Beck et al., 2010), and hydrated amorphous silicates from Potapov et al. (2020). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

by Potapov et al. (2020) that studied the IR properties of ice-silicate mixtures (see Fig. 8b), that were progressively heated up to 200 K. As argued by Potapov et al. (2020), the interaction with water-ice grains can trap water molecules within or on the surface of amorphous silicates; the incorporated water molecules are tightly bonded to the amorphous silicates, which can help in delivering water in the inner part of the protoplanetary disks. Our AFM-IR observation on the CR chondrite EET 92042 provides evidence that such hydrated amorphous silicates were indeed present in the early solar system. Because these water molecules are more tightly bonded than within the water-ice structure, these hydrated amorphous silicates therefore could have played a role in delivering water to the inner solar system and then terrestrial planets.

## Precipitates: Carbonates and Sulfates

### Carbonate Mineralogy

Both in EET 92042 and Orgueil, an absorption around 1400–1500 cm⁻¹ was observed, which we

interpret by the presence of carbonates (Fig. 6). Looking at these peaks in more detail, the exact position differs in Orgueil and EET 92042, with a peak maximum around 1440 cm⁻¹ for the CI and around 1470 cm⁻¹ for the CR chondrites. This difference points toward different mineralogy of the carbonates present in both samples (Lane & Christensen, 1997). Also, while pure carbonate spectra were obtained for the CR chondrite, the carbonate signatures in Orgueil were always found in association with the sulfate signature (see the section below) (Figs. 6a and 7b).

The carbonate-rich region in EET 92042 presents a strong absorption peak at 1470 cm⁻¹, together with smaller features around 1780 and 860 cm⁻¹ (Figs. 6b and 8a). They do not show features at 1630 cm⁻¹, which rules out the presence of hydrocarbonates. The position of the peak found for carbonates in EET 92042 using AFM-IR is in good agreement with the carbonate-related feature in the spectra of a carbonate-rich matrix fragment measured with FTIR (EET92042#P19, green spectrum of Fig. 8a). Comparison with carbonate spectra from the literature reveals that dolomite, calcite, or siderite do not
match the position of the infrared peaks obtained for EET 92042 carbonates. On the contrary, comparison to infrared spectra of aragonite provides a fair match to AFM-IR measurements of carbonates in EET 92042 (Fig. 8a).

Previous works have shown that carbonates in CR chondrites are mostly calcium-rich (Brearley, 2006; Jilly-Rehak et al., 2018; Weisberg et al., 1993), but little is known on their exact crystal structure. In the case of seawater, the nature of the CaCO₃ polymorph that can precipitate depends on both the temperature and Mg/Ca ratio of the solution (Morse et al., 1997). An elevated Mg/Ca ratio will favor the formation of aragonite rather than calcite (e.g., Mg/Ca >5 at T = 8 °C), while for a given Mg/Ca ratio, low temperature will favor the precipitation of calcite (at Mg/Ca = 1, calcite will precipitate if T < 20 °C; Morse et al., 1997).

Aragonite has been identified in CM chondrites, and its abundance depends on the petrological subtype (Lee & Ellen, 2008; Lee & Lindgren, 2015; Lee et al., 2014). It was found that the abundance of aragonite decreases with an increasing extent of aqueous alteration, which suggests that aragonite was possibly the first carbonate to crystallize in the aqueous alteration sequence defined by Lee et al. (2014). Our possible detection of aragonite in EET 92042 may be explained by a relatively low level of aqueous alteration and precipitation from a fluid that experienced little chemical fractionation.

## Which Sulfate Is in Orgueil?

As evidenced from the map obtained at 1150 cm⁻¹, the second most frequent IR signature observed in Orgueil (after phyllosilicates) is that interpreted as sulfate (Fig. 4d). Such a signature reveals absorption at 1150, 1090, and 980 cm⁻¹ (e.g., Fig. 7a). A broad feature around 1660 cm⁻¹ is also associated with these sulfate signatures (interpreted by structural H₂O) as well as an absorption around 1450 cm⁻¹ interpreted as a carbonate signature. To identify the nature of the sulfate present in Orgueil, the spectra obtained using AFM-IR were compared to literature spectra of sulfate of various compositions. While no perfect match was found, the closest spectra identified in the literature are copiapite, an iron-bearing hydrated sulfate (Fig. 7b). While Ca- and Mg-rich sulfate has been described in Orgueil in the form of large veins, the sulfate found at the very small scale in our sample of Orgueil seems to fairly match with basanite (CaSO₄·0.5H₂O) spectrum at 1145 and 1090 cm⁻¹ as previously described in Liu (2018). It is possible that the sulfate in Orgueil is a component of epsomite and bassanite, as observed by SEM-EDS in the previous study (Brearley & Jones, 1996). Copiapite can be found on Earth as an alteration

of iron sulfide. Therefore, if indeed copiapite, the sulfate found in the fine-grained matrix of Orgueil could be a decomposition product of primary iron sulfide that was formed during aqueous alteration on the CI parent body, or during terrestrial residence similar to sulfate veins (Gounelle & Zolensky, 2001).

It was found by Tomeoka and Buseck (1988) that the phyllosilicate in Orgueil is intimately mixed with an Fe-, S-, and Ni-rich phase. Since ferrihydrite was identified based on the selected area electron diffraction pattern, the Fe-S-Ni associate was interpreted by the presence of sulfate and Ni ion adsorbed onto the ferrihydrite. It is possible that the sulfate signature observed in the present work corresponds to adsorbed sulfate ions on a ferrihydrite surface, but we do not know yet the spectral signature of such an association.

## CONCLUSION

We applied AFM-IR with the latest platform NanoIR3s to access meteoritic composition with nanometer-scale resolution within high and low altered chondrites and their IOMs. We achieved ~20 nm spatial resolution on taping imaging and ~150 nm lateral resolution on contact spectroscopy, which is beyond the diffraction limit. AFM-IR analysis successfully separates the signatures of organic-mineral association to (1) unmix the spectral signature of the phyllosilicate from that of other matrix constituents and organic matter for the first time in Orgueil and observe the changes of structure in macromolecular hydrocarbon under the chemical extraction; (2) give more evidence of hydrated amorphous silicates present in the early solar system through the AFM-IR spectra on the CR chondrite EET 92042; (3) find out the exact carbonate crystal structure both in CR and CI chondrites; (4) observe the sulfate signature in Orgueil (CI) similar to the mixture of basanite and epsomite. In addition, using the AFM-IR technique, we are not only able to image the functional groups of organics similar to the C K-edge XANES/STXM technique but also access to the mineralogy similar to TEM analysis. Finally, the present work clearly shows that AFM-IR is a useful technique and suitable for Ryugu asteroid samples, as well as interplanetary dust particles and other primitive solar system materials.

*Acknowledgments*—The authors are grateful for the financial support of the H2020 European Research Council (ERC) (SOLARYS ERC-CoG2017_771691) and the Programme National de Planétologie (PNP) as well as the Centre national d'études spatiales (CNES) within the framework of the Hayabusa2 and MMX missions. We acknowledge Frédéric Charlot for the assistance during FIB preparation at CEA/CMTC
(Grenoble, France). We also acknowledge Minako Takase, who helped to prepare the sulfur-embedded microtome section for AFM-IR analysis at the microscopy platform of Kyushu University (Fukuoka, Japan).

*Data Availability Statement*—The supporting data related to this article are also available in its Supporting Information (https://doi.org/10.1111/maps.13773).

*Editorial Handling*—Dr. Daniel Glavin

## REFERENCES

Abreu, N. M., and Brearley, A. J. 2010. Early Solar System Processes Recorded in the Matrices of Two Highly Pristine CR3 Carbonaceous Chondrites, MET 00426 and QUE 99177. *Geochimica et Cosmochimica Acta* 74: 1146–71. https://doi.org/10.1016/j.gca.2009.11.009

Alexander, C. M. O'D., Cody, G. D., De Gregorio, B. T., Nittler, L. R., and Stroud, R. M. 2017. The Nature, Origin and Modification of Insoluble Organic Matter in Chondrites, the Major Source of Earth's C and N. *Chemie der Erde* 77: 227–56. https://doi.org/10.1016/j.chemer.2017.01.007.

Alexander, C. M. O'D., Fogel, M., Yabuta, H., and Cody, G. D. 2007. The Origin and Evolution of Chondrites Recorded in the Elemental and Isotopic Compositions of Their Macromolecular Organic Matter. *Geochimica et Cosmochimica Acta* 71: 4380–403. https://doi.org/10.1016/j.gca.2007.06.052.

Alexander, C. M. O'D., Newsome, S. D., Fogel, M. L., Nittler, L. R., Busemann, H., and Cody, G. D. 2010. Deuterium Enrichments in Chondritic Macromolecular Material—Implications for the Origin and Evolution of Organics, Water and Asteroids. *Geochimica et Cosmochimica Acta* 74: 4417–37. https://doi.org/10.1016/j.gca.2010.05.005.

Amari, S., Lewis, R. S., and Anders, E. 1994. Interstellar Grains in Meteorites: I. Isolation of SiC, Graphite and Diamond; Size Distributions of SiC and Graphite. *Geochimica et Cosmochimica Acta* 58: 459–70. https://doi.org/10.1016/0016-7037(94)90477-4

Beck, P., Garenne, A., Quirico, E., Bonal, L., Montes-Hernandez, G., Moynier, F., and Schmitt, B. 2014. Transmission Infrared Spectra (2–25 lm) of Carbonaceous Chondrites (CI, CM, CV-CK, CR, C2 Ungrouped): Mineralogy, Water, and Asteroidal Processes. *Icarus* 229: 263–77. https://doi.org/10.1016/j.icarus.2013.10.019.

Beck, P., Quirico, E., Montes-Hernandez, G., Bonal, L., Bollard, J., Orthous-Daunay, F.-R., Howard, K. T. et al. 2010. Hydrous Mineralogy of CM and CI Chondrites from Infrared Spectroscopy and Their Relationship with Low Albedo Asteroids. *Geochimica et Cosmochimica Acta* 74: 4881–92. https://doi.org/10.1016/j.gca.2010.05.020.

Bonal, L., Alexander, C. M. O'D., Huss, G. R., Nagashima, K., Quirico, E., and Beck, P. 2013. Hydrogen Isotopic Composition of the Water in CR Chondrites. *Geochimica et Cosmochimica Acta* 106: 111–33. https://doi.org/10.1016/j.gca.2012.12.009.

Brearley, A. J. 2006. The Action of Water. In *Meteorites and the Early Solar System II*, edited by D. S. Lauretta and H. Y. Mcsween Jr., 587–624. Tucson, Arizona: The University of Arizona Press.

Brearley, A. J., and Jones, R. H. 1996. Chondritic Meteorites. In *Planetary Materials*, edited by J. J. Papike, 3-001-3.398. Reviews in Mineralogy, vol. 36. Washington, D.C.: Mineralogical Society of America.

Bruker 2019. nanoIR3 User Guide (April).

Changela, H. G., Guillou, C. L. E., Bernard, S., and Brearley, A. J. 2018. Hydrothermal Evolution of the Morphology, Molecular Composition, and Distribution of Organic Matter in CR (Renazzo-Type) Chondrites. *Meteoritics & Planetary Science* 53: 1006–29. https://doi.org/10.1111/maps.13045.

Cody, G. D., and Alexander, C. M. O'D. 2005. NMR Studies of Chemical Structural Variation of Insoluble Organic Matter from Different Carbonaceous Chondrite Groups. *Geochimica et Cosmochimica Acta* 69: 1085–97. https://doi.org/10.1016/j.gca.2004.08.031.

Crovisier, J., Leech, K., Bockelée-Morvan, D., Brooke, T. Y., Hanner, M. S., Altieri, B., Keller, H. U., and Lellouch, E. 1997. The Spectrum of Comet Hale-Bopp (C/1995 O1) Observed with the Infrared Space Observatory at 2.9 Astronomical Units from the Sun. *Science* 275: 1904–7. https://doi.org/10.1126/science.275.5308.1904.

Dazzi, A., and Prater, C. B. 2017. AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging. *Chemical Review* 117: 5146–73. https://doi.org/10.1021/acs.chemrev.6b00448.

Dazzi, A., Prater, C. B., Hu, Q., Chase, D. B., Rabolt, J. F., and Marcott, C. 2012. AFM-IR: Combining Atomic Force Microscopy and Infrared Spectroscopy for Nanoscale Chemical Characterization. *Applied Spectroscopy* 66: 1365–84. https://doi.org/10.1366/12-06804.

Dazzi, A., Prazeres, R., Glotin, F., and Ortega, J. M. 2005. Local Infrared Microspectroscopy with Subwavelength Spatial Resolution with an Atomic Force Microscope Tip Used as a Photothermal Sensor. *Optics Letters* 30(18): 2388. https://doi.org/10.1364/ol.30.002388.

Gardinier, A., Derenne, S., Robert, F., Behar, F., Largeau, C., and Maquet, J. 2000. Solid State CP/MAS 13C NMR of the Insoluble Organic Matter of the Orgueil and Murchison Meteorites: Quantitative Study. *Earth and Planetary Science Letters* 184: 9–21. https://doi.org/10.1016/S0012-821X(00)00300-9.

Glavin, D. P., Alexander, C. M. O'D., Aponte, J. C., Dworkin, J. P., Elsila, J. E., and Yabuta, H. 2018. The Origin and Evolution of Organic Matter in Carbonaceous Chondrites and Links to Their Parent Bodies. In *Primitive Meteorites and Asteroids: Physical, Chemical, and Spectroscopic Observations Paving the Way to Exploration*, edited by N. Abreu, 205–71. Amsterdam: Elsevier. https://doi.org/10.1016/B978-0-12-813325-5.00003-3.

Gooding, J. L., Wentworth, S. J., and Zolensky, M. E. 1988. Calcium Carbonate and Sulfate of Possible Extraterrestrial Origin in the EETA79001 Meteorite. *Geochemical Perspectives Letters* 52: 909–15.

Gounelle, M., and Zolensky, M. E. 2001. A Terrestrial Origin for Sulfate Veins in CI1 Chondrites. *Meteoritics & Planetary Science* 36: 1321–9. https://doi.org/10.1111/j.1945-5100.2001.tb01827.x.

Jilly-Rehak, C. E., Huss, G. R., Nagashima, K., and Schrader, D. L. 2018. Low-Temperature Aqueous
Alteration on the CR Chondrite Parent Body: Implications from In Situ Oxygen-Isotope Analyses. *Geochimica et Cosmochimica Acta* 222: 230–52. https://doi.org/10.1016/j.gca.2017.10.007.

Kebukawa, Y., Alexander, C. M. O'D., and Cody, G. D. 2011. Compositional Diversity in Insoluble Organic Matter in Type 1, 2 and 3 Chondrites as Detected by Infrared Spectroscopy. *Geochimica et Cosmochimica Acta* 75: 3530–41. https://doi.org/10.1016/j.gca.2011.03.037.

Kebukawa, Y., Kobayashi, H., Urayama, N., Baden, N., Kondo, M., Zolensky, M. E., and Kobayashi, K. 2018. Nanoscale Infrared Imaging Analysis of Carbonaceous Chondrites to Understand Organic-Mineral Interactions During Aqueous Alteration. *Proceedings of the National Academy of Sciences* 116: 753–8. https://doi.org/10.1073/pnas.1816265116.

King, A. J., Solomon, J. R., Schofield, P. F., and Russell, S. S. 2015. Characterising the CI and CI-Like Carbonaceous Chondrites Using Thermogravimetric Analysis and Infrared Spectroscopy. *Planetary Science. Earth, Planets and Space.* 67: 198. https://doi.org/10.1186/s40623-015-0370-4.

Lane, M. D., and Christensen, P. R. 1997. Thermal Infrared Emission Spectroscopy of Anhydrous Carbonates. *Journal of Geophysical Research E: Planets* 102: 25581–92. https://doi.org/10.1029/97JE02046.

Le Guillou, C., Bernard, S., Brearley, A. J., and Remusat, L. 2014. Evolution of Organic Matter in Orgueil, Murchison and Renazzo During Parent Body Aqueous Alteration: In Situ Investigations. *Geochimica et Cosmochimica Acta* 131: 368–92. https://doi.org/10.1016/j.gca.2013.11.020.

Le Guillou, C., Changela, H. G., and Brearley, A. J. 2015. Widespread Oxidized and Hydrated Amorphous Silicates in CR Chondrites Matrices: Implications for Alteration Conditions and H2 Degassing of Asteroids. *Earth and Planetary Science Letters* 420: 162–73. https://doi.org/10.1016/j.epsl.2015.02.031.

Lee, M. R., and Ellen, R. 2008. Aragonite in the Murray (CM2) Carbonaceous Chondrite: Implications for Parent Body Compaction and Aqueous Alteration. *Meteoritics & Planetary Science* 43: 1219–31. https://doi.org/10.1111/j.1945-5100.2008.tb01124.x.

Lee, M. R., and Lindgren, P. 2015. 4.6-Billion-Year-Old Aragonite and its Implications for Understanding the Geological Record of Ca-Carbonate. *Carbonates and Evaporites* 30: 477–81. https://doi.org/10.1007/s13146-015-0257-2.

Lee, M. R., Lindgren, P., and Sofe, M. R. 2014. Aragonite, Breunnerite, Calcite and Dolomite in the CM Carbonaceous Chondrites: High Fidelity Recorders of Progressive Parent Body Aqueous Alteration. *Geochimica et Cosmochimica Acta* 144: 126–56. https://doi.org/10.1016/j.gca.2014.08.019.

Liu, Y. 2018. Raman, Mid-IR, and NIR Spectroscopic Study of Calcium Sulfates and Mapping Gypsum Abundances in Columbus Crater, Mars. *Planetary and Space Science* 163: 35–41. https://doi.org/10.1016/j.pss.2018.04.010.

Mathurin, J., Dartois, E., Pino, T., Engrand, C., Duprat, J., Deniset-Besseau, A., Borondics, F., Sandt, C., and Dazzi, A. 2019. Nanometre-Scale Infrared Chemical Imaging of Organic Matter in Ultra-Carbonaceous Antarctic Micrometeorites (UCAMMs). *Astronomy & Astrophysics* 160: 1–9.

Mathurin, J., Pancani, E., Deniset-Besseau, A., Kjoller, K., Prater, C. B., Gref, R., and Dazzi, A. 2018. How to

Unravel the Chemical Structure and Component Localization of Individual Drug-Loaded Polymeric Nanoparticles by Using Tapping AFM-IR. *Analyst* 143: 5940–9. https://doi.org/10.1039/c8an01239c.

Morse, J. W., Wang, Q., and Tsio, M. Y. 1997. Influences of temperature and Mg:Ca ratio on CaCO3 precipitates from seawater. *Geology* 25(1): 85–87. https://doi.org/10.1130/0091-7613(1997)025<0085:IOTAMC>2.3.CO;2

Noguchi, T., Takase, M., Matsumoto, R., Kebukawa, Y., Suga, H., Kondo, M., Takahashi, Y., Takeichi, Y., and Yabuta, H. 2020. An Another Protocol to Make Sulfur Embedded Ultrathin Sections of Extraterrestrial Small Samples. *Life* 10: 1–13.

Orthous-Daunay, F. R., Quirico, E., Beck, P., Brissaud, O., Dartois, E., Pino, T., and Schmitt, B. 2013. Mid-Infrared Study of the Molecular Structure Variability of Insoluble Organic Matter from Primitive Chondrites. *Icarus* 223: 534–43. https://doi.org/10.1016/j.icarus.2013.01.003.

Orthous-Daunay, F.-R., Quirico, E., Beck, P., Brissaud, O., and Schmitt, B. 2010. Structural and Functional Micro-Infrared Survey of Pristine Carbonaceous Chondrites Insoluble Organic Matter (abstract #1803). 41st Lunar and Planetary Science Conference. CD-ROM.

Painter, P. P., Snyder, R. W., Starsinic, M., Coleman, M. M., Kuehn, D. W., and Davis, A. 1981. Concerning the Application of FT-IR to the Study of Coal: A Critical Assessment of Band Assignments and the Application of Spectral Analysis Programs. *Applied Spectroscopy* 35: 475–85. https://doi.org/10.1366/0003702814732256.

Pearson, V. K., Sephton, M. A., Kearsley, A. T., Bland, P. A., Franchi, I. A., and Gilmour, I. 2002. Clay Mineral-Organic Matter Relationships in the Early Solar System. *Meteoritics & Planetary Science* 37: 1829–33. https://doi.org/10.1111/j.1945-5100.2002.tb01166.x

Petersen, H. I., Rosenberg, P., and Nytoft, H. P. 2008. Oxygen Groups in Coals and Alginite-Rich Kerogen Revisited. *Coal Geology* 74: 93–113. https://doi.org/10.1016/j.coal.2007.11.007.

Phan, V. T. H., Quirico, E., Beck, P., Le Brech, Y., Jovanovic, L., Le Guillou, C., Bernard, S. et al. 2021. Infrared Spectroscopy Quantification of Functional Carbon Groups in Kerogens and Coals: A Calibration Procedure. *Spectrochimica Acta—Part A: Molecular and Biomolecular Spectroscopy* 259: 119853. https://doi.org/10.1016/j.saa.2021.119853.

Potapov, A., Bouwman, J., Jäger, C., and Henning, T. 2020. Dust/Ice Mixing in Cold Regions and Solid-State Water in the Diffuse Interstellar Medium. *Nature Astronomy* 5: 78–85. https://doi.org/10.1038/s41550-020-01214-x.

Quirico, E., and Bonal, L. 2019. Organic Matter in Interplanetary Dusts and Meteorites. In *Biosignatures for Astrobiology*, edited by Cavalazzi, B. and Westall, F., 23–50. Cham, Switzerland: Springer Nature AG2019. https://doi.org/10.1007/978-3-319-96175-0_2.

Quirico, E., Bonal, L., Beck, P., Alexander, C., Yabuta, H., Nakamura, T., Nakato, A. et al. 2018. Prevalence and Nature of Heating Processes in CM and C2-Ungrouped Chondrites as Revealed by Insoluble Organic Matter. *Geochimica et Cosmochimica Acta* 241: 17–37. https://doi.org/10.1016/j.gca.2018.08.029.

Quirico, E., Orthous-Daunay, F.-R., Beck, P., Bonal, L., Brunetto, R., Dartois, E., Pino, T. et al. 2014. Origin of Insoluble Organic Matter in Type 1 and 2
Chondrites: New Clues, New Questions. *Geochimica et Cosmochimica Acta* 136: 80–99. https://doi.org/10.1016/j.gca.2014.03.025.

Sandford, S. A. 1986. Laboratory Heating of an Interplanetary Dust Particle: Comparisons with an Atmospheric Entry Model. 17th Lunar and Planetary Science Conference. pp. 754–5.

Sephton, M. A. 2002. Organic Compounds in Carbonaceous Meteorites. *Natural Product Reports* 19: 292–311. https://doi.org/10.1039/b103775g.

Tomeoka, K., and Buseck, P. R. 1988. Matrix Mineralogy of the Orgueil CI Carbonaceous Chondrite. *Geochimica et Cosmochimica Acta* 52: 1627–40. https://doi.org/10.1016/0016-7037(88)90231-1.

## SUPPORTING INFORMATION

Additional supporting information may be found in the online version of this article.

**Fig. S1.** Focus ion beaming using Ga+ ion and depositing procedure on ZnS substrate for AFM-IR measurement: (a) Selecting the interest area on EET 92042 CR2 chondrites; (b) cutting the side trenches and preparing for lift-out; (c) attaching the sample for lift-out using the micromanipulator; (d) attaching the FIB section after lift-out to a Cu-grid; (e) breaking the FIB section from Cu-grid using a tungsten needle; (f) depositing the FIB section on the ZnS substrate.

**Fig. S2.** Comparison of KBr-pellet FTIR, µ-FTIR, and AFM-IR average of (30–100) spectra of mineral

Tomeoka, K., Kojima, H., and Yanai, K. 1989. Yamato-82162: A New Kind of CI Carbonaceous Chondrite Found in Antarctica. *Proceedings of the NIPR Symposium on Antarctic Meteorites* 2: 36–54.

Weisberg, M. K., Prinz, M., Clayton, R. N., and Mayeda, T. K. 1993. The CR (Renazzo-Type) Carbonaceous Chondrite Group and its Implications. *Geochimica et Cosmochimica Acta* 57: 1567–86. https://doi.org/10.1016/0016-7037(93)90013-M.

Yesiltas, M., Glotch, T. D., and Sava, B. 2021. Nano-FTIR Spectroscopic Identification of Prebiotic Carbonyl Compounds in Dominion Range 08006 Carbonaceous Chondrite. *Scientific Reports* 11: 1–9. https://doi.org/10.1038/s41598-021-91200-8.

samples including (a) dolomite, (b) kaolinite, (c) saponite, (d) gypsum, and (e) smectite using both Firefly laser (FF) for the range of 4000–2700 cm⁻¹ and APE laser for the range of 2000–700 cm⁻¹; (f) calcite and (h) antigorite heated at 500 °C using only FF laser; and (g) dunite (pure olivine) and (l) amorphous silicate using only APE laser.

**Fig. S3.** (a) Two sections of sulfur-embedding ultramicrotomy of Orgueil were done by AFM-IR measurement; (b) AFM height image of 2 × 2 µm² areas of Section 3; and (c) AFM-IR single-point spectra in the 2000–800 cm⁻¹ range (labeled S1–S16).

**Fig. S4.** AFM-IR spectrum (red) of polybutadiene shows a good correlation with transmission FTIR spectrum (blue).