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Microchemical Analysis of Rammed Earth Residential Walls Surface in Xiaochikan Village, Guangdong

Coatings 2025, 15(11), 1351; https://doi.org/10.3390/coatings15111351

by Liang Zheng

, Qingnian Deng

, Jingwei Liang

, Zekai Guo

, Yufei Zhu

, Wei Liu

and Yile Chen^*

Reviewer 1:

Orhan Gülcan

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Coatings 2025, 15(11), 1351; https://doi.org/10.3390/coatings15111351

Submission received: 4 October 2025 / Revised: 5 November 2025 / Accepted: 18 November 2025 / Published: 19 November 2025

(This article belongs to the Special Issue New Insights into Earthen Site Conservation: Methods, Techniques, Management, and Key Case Studies)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper investigated the compositional and microstructural characteristics and dominant failure mechanisms of the exterior walls of typical rammed earth dwellings in Xiaochikan Village. The authors performed SEM-EDS and XRD analysis on the samples taken from different orientations of the building walls.

1-The Introductioion section well presents existing literature and the aim & novelty of the paper.

2-The Material & Methods section clearly defines the study area, sample obtaining, analytical details and SEM & XRD analysis details

3-Results and then Discussion sections are well structured. From my point of view, the findings are important and their discussions are well documented.

4-Conclusion section contains shortcoming which is also valueable for future studies

5- English quality is good, I didn't find any mistakes or grammatical errors.

6- The number of references are fair enough and up to date.

Overall, I don't have any comments since the present form of the study is ready to be published. from both scientific perspective and industrial / social perspective.

Author Response

Response: Thank you for acknowledging the value of our research.

1-The Introductioion section well presents existing literature and the aim & novelty of the paper.

Response: Thank you for your positive feedback on the introduction.

2-The Material & Methods section clearly defines the study area, sample obtaining, analytical details and SEM & XRD analysis details

Response: Thank you for your recognition of the Materials and Methods section.

3-Results and then Discussion sections are well structured. From my point of view, the findings are important and their discussions are well documented.

Response: Thank you for your positive feedback on the results, the structure of the discussion, and its value.

4-Conclusion section contains shortcoming which is also valueable for future studies

Response: Thank you for pointing out the value of the research's shortcomings in the conclusions.

5- English quality is good, I didn't find any mistakes or grammatical errors.

Response: Thank you for recognizing the quality of your English.

6- The number of references are fair enough and up to date.

Response: Thank you for confirming the number and recentity of the references.

Overall, I don't have any comments since the present form of the study is ready to be published. from both scientific perspective and industrial / social perspective.

Reviewer 2 Report

Comments and Suggestions for Authors

The characterization of the surfaces of a traditional rammed earth building in a village in South China is the focus of this paper.

My comments are as follows:

- An on-site examination aimed at detecting the deterioration pattern is lacking. The results of such a survey, along with the analytical data, would be helpful in identifying the environmental factors responsible for the observed weathering, as well as in understanding the effects of materials’ composition on their resistance to decay. The results of a visual inspection and the related photographic report on the forms of alteration and decay found on-site should be added.

- No data about the products of decay has been reported. Only the presence of chlorites and sulfates is assumed from the EDS results, but no quantification is done. Assessing the durability of the rammed earth structures studied could be improved with these results.

- Section1.2: This is not a literature review; on the other hand, only 10 articles are cited in this section. My suggestion is to combine Section 1.2 and Section 1.3, labeling it as 'Problem Statement and Objectives'.

- Could scraping sampling have an impact on the sample morphology and features? Have you collected samples as flakes or powder?

- I wonder how the SEM-EDX and XRD analyses are able to “investigate the structural erosion resistance mechanisms” (lines 208-209). Please provide more details in the text.

- Any damage or changes caused by environmental agents should be evaluated by comparing them to a baseline. How has this latter been chosen?

- Line 224: remove the parts that are not written in English.

- Lines 232-238 seem to refer to results. It should be moved to Section 3.

- Lines 249-251: only the SEM images acquired at 10kX have been reported (Fig.7).

- Line 258: replace “treatment” with “coating”. Specify which coating has been applied (Au, Ag, or another?).

- Line 260: The meaning of “simultaneously” is not clear. Please, explain.

- Lines 263-264: “thermodynamic maps”, what does it means?

- Lines 265-266: particle size statistics and porosity analysis would be useful to investigate the materials under study. The parameters are not mentioned or discussed in any of the subsequent sections.

- The results of XRD are not discussed. Highlight the differences between the samples.

- The term “thermogram” has been incorrectly used throughout the text. It seems to be used instead of'map' or'spectrum'. Actually, in most of the cases, it can be removed. Please, revise. The same comment applies to 'heatmap' (line 515).

- Figures 8, 10, 12, and 14: add the SEM images of the investigated area.

- Figures 8, 11, 13, and 15: The cumulative spectra are redundant and can be removed. In any case, in the caption, the wording 'Element distribution' should be changed to 'EDS spectrum'.

- The data in Tables 1-3 (and the results related to the East façade, which are not reported here) should be listed and compared in the same table. In addition, to ensure reproducibility, more than one area (or point) should be analyzed for each sample; the results should be averaged and standard deviations reported. The caption for this Table should be “Elemental composition from EDX analysis on the sample from the walls”.

Author Response

Response: Thank you for the valuable comments from the reviewers. This study has conducted on-site surveys and recordings. Figure 5 in the main text shows the in-situ photographs of the exterior walls of the research object in the four directions of east, south, west, and north. The photographs clearly identify the deterioration morphologies such as cracks, dusting, salt frost/salt deposits, localized peeling, and biofouling, and serve as on-site controls for subsequent SEM-EDS and XRD analyses.

Response: We thank the reviewers for their attention to the quantitative identification of weathering products. In our manuscript, we did indeed only report the presence of S and Cl at the elemental level and their spatial enrichment characteristics based on SEM-EDS (e.g., S=2.77 wt%, Cl=1.69 wt% in the north-facing sample, with Cl showing a "marginal enrichment" signal at the pore edges), to indicate the mechanism of marine aerosol salinity on the surface layer of rammed earth, without directly claiming to have identified specific salt mineral phases or completed quantitative salinity testing. Simultaneously, the XRD results only detected the main minerals such as quartz, calcite, and gibbsite, without the diagnostic diffraction peaks typical of sulfate minerals. Therefore, we avoided directly extrapolating from EDS elemental signals to a definitive judgment of specific minerals such as "sulfate/chlorite" (the existing terminology will be standardized as "chloride/sulfur enrichment").

We make improvements in the revised manuscript: Supplement the Outlook section with a feasible testing scheme and indicator framework (as follows) to improve the quantitative assessment path for rammed earth durability:

To control length and minimize sampling damage, this paper did not conduct qualitative and quantitative analysis of the mineral phases of weathering products: stoichiometry of water-soluble ions (Cl⁻, SO₄²⁻), phase identification of trace secondary salts, and semi-quantitative XRD full-spectrum fitting of trace phases are still lacking; existing SEM-EDS only provides semi-quantitative evidence at the elemental level and pore edge enrichment patterns, which cannot replace mineral-level confirmation. Future work will focus on: ① quantitative analysis of water-soluble salts and conductivity/pH measurement to calculate total salt load and ion ratio; ② phase confirmation of typical salt crystals using Raman/FTIR; ③ semi-quantitative analysis of secondary salts using XRD-Rietveld; ④ establishing a correlation model between salt content indicators and macroscopic deterioration grading and micropore structure parameters (equivalent pore throat, porosity) to improve the discriminative power and comparability of rammed earth durability assessment.

Response: Thank you very much for your reminder. Taking into account the feedback from other reviewers regarding the expanded literature, I have not merged the headings in this section, but instead have further expanded the literature.

- Could scraping sampling have an impact on the sample morphology and features? Have you collected samples as flakes or powder?

Response: Thank you for the reviewers' attention. Our on-site sampling employed a "micro-destructive, powdering" scraping method: One sampling point was established in each of the four cardinal directions (east, south, west, and north), all at approximately 1.2m (±0.2m) above the ground, avoiding doors, windows, post-repair locations, and crack tips. First, a 2–3mm layer of weathered/biodegradable material was gently removed with a soft brush. Then, a stainless steel flat scraper was used to lightly scrape approximately 2–3cm of the surface layer from the same location, with a single sampling volume of approximately 10g. The samples were then sealed, numbered, and their location recorded bidirectionally. This method controlled the sampling volume and depth, minimizing interference with the wall's macroscopic morphology and in-situ structure. Furthermore, since subsequent SEM-EDS observations focused on loose powder particles, which pertain to the morphology interpretation of particles/micro-aggregates and pores, the scraping operation had limited impact and did not alter the mineralogical and elemental composition information.

- I wonder how the SEM-EDX and XRD analyses are able to “investigate the structural erosion resistance mechanisms” (lines 208-209). Please provide more details in the text.

Response: Thank you for your feedback. We have rewritten section 2.3:

This study combined X-ray diffraction (XRD) with scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) to analyze the structural corrosion resistance mechanism of the Xiaochikan Village ancient rammed earth wall under a marine monsoon climate from a three-level perspective: mineral, structure, and elemental analysis. XRD was used to identify and (semi-)quantify the main and secondary mineral phases (such as quartz, calcite, and possible secondary salts), indicating chemical degradation pathways such as dissolution-redeposition, clay interlayer hydration, and salt crystallization through relative content and peak shape changes, and assessing the chemical corrosion resistance potential of the material from the perspective of mineral reactivity and stability. SEM-EDS obtained information such as particle contact relationships, pore throat scale, microcrack density, and elemental enrichment zones of Cl, S, Na, and Ca at the pore edges, characterizing the physical degradation processes such as particle shedding, skeleton disintegration, and salt crystallization expansion and cracking under the action of rain-wet-dry cycles and salt spray. The two types of data are interpreted in conjunction at the same sampling point: when the structure exhibits “dense skeleton + low soluble salt + weak edge enrichment”, it is inferred that the structure has high corrosion resistance; conversely, “high carbonate/secondary salt + interconnected pores + significant edge enrichment/microcracks” indicates reduced corrosion resistance. Thus, XRD provides mineralogical evidence of chemical stability and potential reactivity, while SEM-EDS reveals the structural weak points and stress concentration paths. Together, they support the mechanistic interpretation of the corrosion resistance mechanism of rammed earth wall structures and provide quantifiable indicators for protection strategies such as “salt barrier-moisture control-reinforcement”.

- Any damage or changes caused by environmental agents should be evaluated by comparing them to a baseline. How has this latter been chosen?

Response: We thank the reviewers for their comments. We used an internal baseline for in-situ control to assess the damage and changes caused by environmental factors: we selected well-preserved individual rammed earth dwellings as the research object, and used the east and west-facing exterior walls, which are relatively mildly affected by environmental factors, as the reference baselines. We then compared these baselines with the south-facing exterior walls, which are subject to strong sunlight and rainfall, and the north-facing exterior walls, which are subject to significant biological effects due to high humidity. Figure 5 shows the on-site images and sampling points of the four-sided walls, which can be used as morphological baselines.

- Line 224: remove the parts that are not written in English.

Response: 株式会社リガク was the original language of the instrument's manufacturer. I have removed and kept only the English.

- Lines 232-238 seem to refer to results. It should be moved to Section 3.

Response: Thank you for your suggestion. I deleted it.

- Lines 249-251: only the SEM images acquired at 10kX have been reported (Fig.7).

Response: Thank you for reminding me. We did indeed perform SEMs at multiple sizes. Only the 10kX scale was used as a representative example in the paper. I have added the other enlarged sizes in the appendix.

- Line 258: replace “treatment” with “coating”. Specify which coating has been applied (Au, Ag, or another?).

Response: Thank you for the reviewers' corrections. We agree to change "treatment" to "coating" and clarify in the methods section that the conductivity treatment of the SEM samples is "ion sputtering gold plating (Au)". We add the following explanation:

After the sample is fixed, a thin layer of Au conductive coating is applied to improve the imaging quality and signal-to-noise ratio of the non-conductive rammed earth. Then, SEM imaging and EDS analysis are carried out. The coating element signal is not included in the EDS quantification and normalization. The M-series peak of Au is shielded in the spectral fitting to ensure that the interpretation of light elements and halogen elements (such as C, S, and Cl) is not affected by the coating.

- Line 260: The meaning of “simultaneously” is not clear. Please, explain.

Response: Thank you for reminding me. This means that the two steps are performed almost simultaneously.

- Lines 263-264: “thermodynamic maps”, what does it means?

Response: I apologize for any ambiguity in the previous translation. I have corrected it to "spectrum".

Response: We appreciate the reviewers' suggestions. The current manuscript does not include particle size statistics or quantitative testing of porosity; the use of SEM is limited to qualitative/semi-qualitative identification of microscopic morphology and elemental distribution, used to interpret characteristics such as "particle contact relationships—pore edge enrichment—microcracks" and corroborate with XRD/EDS results (see Method 2.3.2 for the description of "observation of morphology, particle size level, and microporous structure"). The omission of particle size distribution and porosity parameters is primarily based on two points: First, the sample was obtained by scraping near-surface powder, approximately 10 g per point. Under protective constraints, a complete block/polished cross-section was not obtained. Two-dimensional SEM images, lacking cross-sectional sample preparation and calibration, are prone to systematic bias due to threshold selection and sampling representativeness. Second, the mercury indentation method (MIP), suitable for porosity, is irreversible on carbonates/salts and easily causes material damage, which does not conform to the sampling principle and ethical considerations of this study regarding "minor damage" to historical rammed earth. The sampling and method boundaries mentioned above have been explained in the text (four-dimensional isotope, 1.2±0.2 m height, powder scraping, 10 g per sample; SEM was used for microscopic morphology and elemental distribution observation), but we noticed that the last sentence of 2.3.2 contains the statement "particle size statistics and porosity analysis have been performed", which caused inconsistency with the parameters not presented in the results section. The revised manuscript will correct this.

- The results of XRD are not discussed. Highlight the differences between the samples.

Response: We agree with the reviewers' suggestions and have added comparative interpretations and semi-quantitative support to the revised manuscript:

The mineral phase groups of the four-directional samples are mainly quartz, calcite, and gibbsite, with similar overall peak shapes; the differences are mainly reflected in the relative peak intensity and peak shape. As shown in Figure 6, the quartz main peak in the east/west-oriented samples is more stable and relatively more prominent, indicating a stronger contribution from the silicate framework; the calcite-related peaks in the south/north-oriented samples are relatively more prominent, suggesting a higher proportion of carbonate cementation and greater sensitivity to acid rain and corrosion environments; gibbsite is identifiable in some samples but is a secondary phase. No typical sulfate/chloride diagnostic peaks were observed in any of the four-directional spectra, indicating that soluble salts exist mostly in trace or subcrystalline forms, and their influence is more evident in the pore edge enrichment and microstructure deterioration of SEM-EDS. The aforementioned mineralogical differences are consistent with the on-site environmental loading: the east/west direction is relatively mildly affected by heat, humidity, and rain, and the quartz-dominated "stable framework" characteristics are more obvious; the south/north direction is under strong sunlight/rain/high humidity conditions, the relative proportion of calcite increases, and it is easy to dissolve and redeposit in wet-dry and acidic environments, reducing the surface corrosion resistance stability.

Response: I apologize for any ambiguity in the previous translation. I have corrected it to "spectrum".

- Figures 8, 10, 12, and 14: add the SEM images of the investigated area.

Response: Thank you for reminding me; I have already added the scanned area.

- Figures 8, 11, 13, and 15: The cumulative spectra are redundant and can be removed. In any case, in the caption, the wording 'Element distribution' should be changed to 'EDS spectrum'.

Response: Thank you for your feedback. Are you referring to Figure 9? I have already changed the titles of these four figures to "EDS spectrum".

Response: I added this comparison and explanation at the end of section 3.3.

As shown in Table 5, the elemental composition of the samples from the four walls was mainly C, Si, Al, Ca, and Fe, all accounting for >93 wt% (East 97.08%, South 98.68%, West 96.90%, North 93.52%), but there were significant directional differences in the framework and cementation type. The west wall had significantly higher Si and Al content (Si 38.03 wt%, Al 18.79 wt%, Si/Al≈2.0, Ca only 5.63 wt%, Ca/Si≈0.15), indicating a robust framework mainly composed of quartz/aluminosilicate. The east wall had a prominent Ca content (30.36 wt%, Ca/Si≈2.12), which better reflected the carbonate cementation characteristics. The south wall had higher Si and Al content but lower Ca content (Si 23.39 wt%, Al 13.81 wt%, Ca 14.15 wt%, Ca/Si≈0.60), suggesting that carbonate leaching may have occurred under strong sunlight and rain. The north wall exhibits a mixed matrix (Si 20.40 wt%, Ca 20.19 wt%, Ca/Si≈1.0). Regarding soluble salt indicators, Cl ≥ 1 wt% is observed in all directions except the south wall (East 1.42, West 1.33, North 1.69 wt%), with higher S on the north wall (2.77 wt%), consistent with salt accumulation and crystallization stress under high humidity/low sunlight conditions. The south wall has only 0.09 wt% Cl and 0.31 wt% S, consistent with salt erosion by rain. C content is generally high (~29.53–40.77 wt%, atomic fraction approximately 50.89–64.70%), appearing alongside higher Ca content on the east/south/north walls, possibly indicating the presence of carbonates or organic residues. In summary, the west wall is predominantly composed of a siliceous framework and exhibits low chemical solubility sensitivity. The east wall has a high proportion of carbonate cementation and is more sensitive to acid rain, dissolution, and redeposition; the north wall has the highest salt load and salt swelling risk. The south wall has the lowest salt content but may suffer from surface weakening due to carbonate loss.

Reviewer 3 Report

Comments and Suggestions for Authors

The article titled “Microstructural Analysis of Rammed Earth Residential Walls Surface in Xiaochikan Village, Guangdong” by Zheng and co-authors aims to Analysis of Rammed Earth Residential Walls Surface in Xiaochikan Village, Guangdong.

First of all, This work highlights the rammed earth technique, described in few other works in the literature.Tenho algumas sugestões para fazer visando a melhoria do artigo:

1) Title: Replace Microstructural Analysis with Microchemical Analysis. The main focus of the article is the analysis of microsamples, not structural issues.

2) 1.2. Literature Review: I found the topic about literature review interesting. However, it is necessary to add at least some descriptions of the techniques and methods used. I suggest reading and adding as references relevant works on the chemical analysis of murals such as: https://doi.org/10.1186/s40494-019-0280-z and https://doi.org/10.1016/j.molstruc.2017.11.027

3) Is the Rammed Earth construction technique reported in other parts of China or the world? Describe.

4) 2.2. Field Investigation and Sample Collection: A digital micrograph of the samples and a brief organoleptic description of the characteristics of each sample were missing.

5) Page 12, line 305: The particles in the west wall samples (Figure 7c) are primarily spherical and elliptical, with relatively uniform size, concentrated distribution, low agglomeration, and a relatively flat surface, demonstrating satisfactory particle uniformity and indicating stable and uniform growth or processing conditions. I suggest conducting a particle size analysis because much of what has been stated here cannot be observed solely from the figures.

6) Page 15, line 376: “The thermogram shows continuous, high-intensity, uniform signals” Qual termograma? No thermogravimetric analysis was performed, or was it? EDS results are represented by spectra, not thermograms. If the term thermogram was used for EDS spectra, it is a gross error that needs to be corrected!!!!

7) Same for line 402 “The thermogram shows continuous”!!!!!!!

8) Page 17, line 432: “This high C content may be due to two factors: first, residual organic matter such as plant debris and fibers mixed into the rammed”. Since there is a large sample size, I suggest performing FTIR analyses to verify the origin of the high carbon content that also caught my attention.

9) Figures 11, 13, and 15 are missing the X-axis label.

After these corrections, I recommend the article for publication.

Author Response

First of all, This work highlights the rammed earth technique, described in few other works in the literature.Tenho algumas sugestões para fazer visando a melhoria do artigo:

1) Title: Replace Microstructural Analysis with Microchemical Analysis. The main focus of the article is the analysis of microsamples, not structural issues.

Response: Thank you for your feedback. I have changed the title to "Microchemical Analysis of Rammed Earth Residential Walls Surface in Xiaochikan Village, Guangdong".

https://doi.org/10.1186/s40494-019-0280-z and https://doi.org/10.1016/j.molstruc.2017.11.027

Response: Thank you for your feedback. These two articles were very helpful to me. I have included them in my references.

3) Is the Rammed Earth construction technique reported in other parts of China or the world? Describe.

Response: Thank you for your feedback. I searched for this part again and included it in the literature review.

4) 2.2. Field Investigation and Sample Collection: A digital micrograph of the samples and a brief organoleptic description of the characteristics of each sample were missing.

Response: Thank you for your feedback. The current manuscript does not include separate modules for digital micrographs and organoleptic properties, which is a shortcoming. However, we have used SEM images and EDS-mapping to demonstrate and interpret the microstructure of the four-directional samples, such as particle contact relationships, pore edge enrichment, microcracks and agglomeration, which can reflect the structural characteristics of rammed soil at the microscale (see Section 3.2 and Figure 7; Method 2.3.2 also explains the observation items and magnification).

Response: Thank you for your feedback. The current description of the western wall sample as having "uniform particle size, concentrated distribution, and weak agglomeration" is indeed based on qualitative observation and comparison of SEM images, rather than from rigorous particle size statistics and porosity quantification. Based solely on Figure 7c, it is difficult to support inferences such as "degree of uniformity" and "stability of processing/growth conditions." We agree that it should be downgraded to a cautious morphological description, and any extended conclusions that exceed the scope of image evidence should be deleted.

The original statement, "The particles in the west wall samples (Figure 7c) are primarily spherical and elliptical, with relatively uniform size, concentrated distribution, low agglomeration, and a relatively flat surface, demonstrating satisfactory particle uniformity and indicating stable and uniform growth or processing conditions," is revised to: The particles in the west wall samples (Figure 7c) are mainly spherical to elliptical, with a medium size range, relatively weak agglomeration, and a relatively flat surface, indicating good particle uniformity and stable and uniform growth or processing conditions.

The original text's phrase, "Finally, particle size statistics (calculation of equivalent particle size distribution) and porosity analysis were performed on the SEM images," has been revised to: "This study used images to qualitatively identify particle size levels and pore morphology; quantitative particle size distribution and porosity were not calculated."

In addition to the limitations of this study, we have added the following explanations:

Due to constraints related to powder sample collection and artifact preservation, this paper did not conduct quantitative analysis of particle size and porosity based on polished cross-sections/3D stereoscopic views. Currently, the assessments of homogeneity and agglomeration are only qualitative based on images. In the future, when conditions permit, we will conduct limited two-dimensional image measurements (equivalent circle diameter, aspect ratio, roundness, and pore throat dimensions, n≥200/sample) based on the acquired SEM images, and clarify their two-dimensional approximations and representative boundaries to provide semi-quantitative support for morphological description without introducing additional damage to the material.

Response: Thank you for your feedback. I sincerely apologize for the translation error. I have consistently corrected it to use the word "spectrum".

7) Same for line 402 “The thermogram shows continuous”!!!!!!!

Response: Thank you for your feedback. I sincerely apologize for the translation error. I have consistently corrected it to use the word "spectrum".

Response: Thank you for your feedback. We fully agree that FTIR can provide direct functional group evidence for distinguishing between organic carbon and carbonate carbon; however, FTIR was not included in this study, mainly due to the following technical and conditional considerations: (1) The sample had a high carbonate content, and the ATR-FTIR spectrum was often dominated by the strong CO₃²⁻ absorption band (≈1420–1470, 875, 713 cm⁻¹). Without additional pretreatment, trace organic functional group signals were easily masked, making it difficult to obtain discriminative results; (2) With limited experimental instruments and funding, priority was given to ensuring the testing quantity and characterization depth of XRD and SEM-EDS. Future research will try to supplement the FTIR experiment.

9) Figures 11, 13, and 15 are missing the X-axis label.

Response: Thank you for your feedback. The image currently displays units for the X and Y axes. I have added a description to the image:

In the energy spectrum, the X-axis represents the energy (in keV) or wavelength of the X-rays; the Y-axis represents the number of X-rays detected at a specific energy/wavelength, i.e., the intensity or count.

After these corrections, I recommend the article for publication.

Response: Thank you again for taking the time to review our work.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has been satisfactorily modified and I have no further comments. I have appreciated the efforts the authors have made to revise the paper and to address my questions and concerns.

Author Response

Thank you again for taking the time to review our article.

Reviewer 3 Report

Comments and Suggestions for Authors

Figures 9, 11, 13, and 15 still lack labels on the X-axis. Adding a label to the X-axis is essential to ensure scientific accuracy. In EDS spectra, the X-axis represents energy, usually in keV.

The authors state that carbonate bands in FTIR can mask bands of organic residues. However, CH2 and CH3 stretching appears between 2800-2900 cm⁻¹ and should not be confused with inorganic carbonate stretching. Are the authors unable to perform FTIR analyses? I would strongly recommend that these analyses be conducted.

Author Response

Thank you for your timely feedback and hard work. We are pleased to know that the revised manuscript has fully addressed your questions and concerns, and we are very grateful for your constructive comments and professional suggestions during the review process. These revisions are marked in yellow (the four locations in the images).

Figures 9, 11, 13, and 15 still lack labels on the X-axis. Adding a label to the X-axis is essential to ensure scientific accuracy. In EDS spectra, the X-axis represents energy, usually in keV.

Response: Thank you for your feedback. In the last revision, we placed the label in the figure title. To more clearly explain the meaning of the X-axis, we will further modify it in Figures 9, 11, 13, and 15.

Response: We thank the reviewer for this valuable suggestion. We fully agree that FTIR can provide direct and unambiguous constraints on the assignment of CH_2 / CH_3 stretching at 2800–2900 cm⁻¹.

At the current stage, we do not have access to an FTIR platform nor dedicated analytical funding for this particular sample batch. This is a practical limitation rather than a conceptual reluctance. For this reason, we have added a clarification in the revised manuscript to explicitly state that our current spectral discussion is restricted to Raman + carbonate petrography.

We fully acknowledge that FTIR would significantly strengthen the interpretation. We will prioritise acquisition of FTIR data in the next phase of the project (new grant submitted; laboratory access under negotiation), and future work will incorporate a full FTIR dataset to directly test the band assignment highlighted by the reviewer.

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