Measurement report: Ice nucleation ability of perthite feldspar powder

Canet, Julia; Rodriguez, Laura; Renzer, Galit; Alfonso, Pura; Bonn, Mischa; Meister, Konrad; Garcia-Valles, Maite; Verdaguer, Albert

doi:10.5194/egusphere-2025-5014

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https://doi.org/10.5194/egusphere-2025-5014

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23 Oct 2025

| 23 Oct 2025

Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Measurement report: Ice nucleation ability of perthite feldspar powder

Julia Canet, Laura Rodriguez, Galit Renzer, Pura Alfonso, Mischa Bonn, Konrad Meister, Maite Garcia-Valles, and Albert Verdaguer

Abstract. Feldspars are among the most efficient mineral ice-nucleating particles (INPs) in the atmosphere. However, their nucleation behavior varies significantly across natural samples. This study investigates six feldspar powders selected for their perthitic or anti-perthitic textures and spanning a range of K/Na compositions. All samples were comprehensively characterized in terms of mineralogy, bulk and surface chemistry, and microstructure. Droplet freezing assays revealed consistent onset temperatures between −2 and −4 °C, suggesting the presence of shared active nucleation sites across all feldspar types. Cumulative and differential freezing spectra revealed marked differences in the density and distribution of ice-nucleating sites, which were found to correlate with both feldspar composition and microtexture. Using HUB analysis, different subpopulations of ice-nucleating sites were identified. Perthites showing microcline structures exhibited a continuous increase in nucleation site density with decreasing temperature as subpopulations became active. In contrast, samples lacking dominant microcline structures showed plateaus in the cumulative spectra within specific temperature ranges, indicating a significant reduction in certain subpopulations. These findings highlight the crucial role of exsolution textures and crystallographic structure in regulating feldspar ice-nucleation efficiency. The results have implications for understanding feldspar behavior in the atmosphere and for improving predictive models in cloud microphysics.

Received: 13 Oct 2025 – Discussion started: 23 Oct 2025

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Julia Canet, Laura Rodriguez, Galit Renzer, Pura Alfonso, Mischa Bonn, Konrad Meister, Maite Garcia-Valles, and Albert Verdaguer

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RC1: 'Comment on egusphere-2025-5014', Thomas F. Whale, 07 Nov 2025 reply

This study reports measurements of the ice nucleation activity of six well-characterized perthitic feldspars. The work adds to, and in many respects confirms, previous findings reported in Whale et al. (2017) and Kiselev et al. (2021) showing that exsolution textures and resulting structural features are responsible for the high temperature ice nucleation activity (INA) of feldspar then clearly showing that the INA observed at around -15°C may have more to do with level of disorder in the aluminosilicate network. The inclusion of differential nucleus spectra for Whale et al. (2017) data is particularly and represents an analysis we should have performed originally. I also like the picking out of individual modes of nucleation sites for the new data and our previous measurements using the HUB method.

The experiments appear to be very carefully and thoroughly conducted. The paper is clearly written and well-structured. I think it should be published with relatively few changes, though I have quite a few points regarding the discussion which the authors may wish to consider.
Comments

1) The authors may find the LDH1 feldspar data from Daily et al. (2023) of interest. It originates from the same location (Mt Malosa, Malawi) as the TUD#3 sample in Harrison et al. This material, described, perhaps a little hyperbolically, as ‘hyper-active’ in Harrison et al. (2016), appears to eliminate supercooling entirely when present in sufficient quantity—even Snomax and AgI don’t do this. Could you compare this measurement to what you already have? Would it change your conclusions regarding the nature of high temperature feldspar ice nucleation sites?

2) It is important to state how long feldspar samples were in contact with water before ice nucleation measurements. Harrison et al. (2016) demonstrated significant changes in activity over time for some feldspars (see Fig. 4). For example, our purest albite sample started highly active but became much less active after 16 months. The hyperactive TUD#3 feldspar also declined, though less dramatically. While I am not suggesting time-consuming aging experiments here, acknowledging this potential variability and complexity would strengthen the discussion.

3) Regarding the impact of aluminosilicate ordering on the nucleation mode at -15°C – it seems likely that this is still something to do with exposure of the feldspar (100)? Can anything be said about likely differences in the relevant features between orthoclase and microcline? I agree that the evidence points to this (and it may be the main new finding in this work) but it’s not obvious to me why aluminosilicate structural disorder itself should have anything much to do with ice nucleation. Maybe I am missing something.

4) The phrase ‘shared active nucleation sites’ is a little unclear I would say. I agree the sites are most likely very similar in nature, but the measured onset temperatures are still different, so they are in some sense ‘different’. What constitutes ‘shared’? Perhaps I am being too picky here but I think it is wrong to imply that the sites are identical in the way that e.g. ice nucleating proteins might be.

5) More discussion of the findings in Kiselev et al. (2021) would be valuable, particularly the results the for FS08-64 samples (o and c). These samples began as gem-quality sanidines but underwent ion exchange and annealing under different conditions to induce cracks, resulting in distinct cumulative spectra. Their processes may have created both the site population at -5 °C and the colder modes identified in this paper. Could you conduct the HUB analysis on that data? I think this would add significant value.

6) The claim that similar IN behaviour implies comparable geological conditions and analogous surface properties may be overstated to my mind? I think Kiselev et al. (2021) shows that you can probably get similar relevant features on a feldspar surfaces in rather different ways.
Minor comments

The statement “In feldspars, ice preferentially nucleates on the (100) crystallographic face” should cite Kiselev et al. (2017) and Keinert et al. (2022).

I’d make sure that the resolution of Fig. 1(a) is improved in the published version.

I’d check the reference list, there are a few mistakes about, e.g B. J. Murray et al., 2021 rather than Murray et al. 2021 in the text. Kiselev et al. (2017) is incorrectly listed as 2016.
Daily, M. I., Whale, T. F., Kilbride, P., Lamb, S., John Morris, G., Picton, H. M., and Murray, B. J.: A highly active mineral-based ice nucleating agent supports in situ cell cryopreservation in a high throughput format, Journal of The Royal Society Interface, 20, 20220682, doi:10.1098/rsif.2022.0682, 2023.

Harrison, A. D., Whale, T. F., Carpenter, M. A., Holden, M. A., Neve, L., O'Sullivan, D., Vergara Temprado, J., and Murray, B. J.: Not all feldspars are equal: a survey of ice nucleating properties across the feldspar group of minerals, Atmos. Chem. Phys., 16, 10927-10940, 10.5194/acp-16-10927-2016, 2016.

Keinert, A., Deck, K., Gaedeke, T., Leisner, T., and Kiselev, A. A.: Mechanism of ice nucleation in liquid water on alkali feldspars, Faraday Discussions, 235, 148-161, 10.1039/D1FD00115A, 2022.

Kiselev, A., Bachmann, F., Pedevilla, P., Cox, S. J., Michaelides, A., Gerthsen, D., and Leisner, T.: Active sites in heterogeneous ice nucleation—the example of K-rich feldspars, Science, 355, 367-371, 10.1126/science.aai8034, 2017.

Kiselev, A., Keinert, A., Gaedecke, T., Leisner, T., Sutter, C., Petrishcheva, E., and Abart, R.: Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar, Atmos. Chem. Phys. Discuss., 2021, 1-17, 10.5194/acp-2021-18, 2021.

Whale, T. F., Holden, M. A., Kulak, A. N., Kim, Y.-Y., Meldrum, F. C., Christenson, H. K., and Murray, B. J.: The role of phase separation and related topography in the exceptional ice-nucleating ability of alkali feldspars, Physical Chemistry Chemical Physics, 10.1039/C7CP04898J, 2017.

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Citation: https://doi.org/10.5194/egusphere-2025-5014-RC1
RC2:
'Comment on egusphere-2025-5014', Anonymous Referee #2, 15 Nov 2025 reply
Canet et al. presented a study on the immersion freezing activity of 6 feldspar samples to characterize their ice nucleation behaviour. The authors analyzed the chemical composition, minerology, surface area and particle size distribution of those samples, in addition to microscopy images for particle visualization. The authors also applied newly reported data analysis method (i.e., Heterogeneous Underlying-Based (HUB) method) to investigate the contribution of different sub-group of ice nucleation sites. Then, the authors compared their results with those in literature. As a measurement report, the amount of work included in this preprint is sufficient. Unfortunately, following ACP guideline, the presentation quality should be improved before acceptance for publication. We briefly list our general comments as below, followed by more detailed comments. We hope that our comments can help the authors improve this preprint and we encourage the authors to do a resubmission.
General comments:
This preprint is lack of in-depth discussion on interpreting the ice nucleation activity of the samples. For some figures, for instance Figure 4, 6 and 9, even the main information of the data is not sufficiently presented. For example, statements in Line 250-254 are all the text for data in Figure 4, which even did not fully elaborate data in each panel, not mention in-depth discussions for help readers to digest the results.

There are some (mis-) over-interpretations on the data presented in Figure 3 and 8. For example, the statement in Line 218-219 is not consistent with the data shown in Figure 3a which shows the 0.1wt%-sample freezes almost by 100% at -20°C but not like what the authors elaborated: 90% droplets remained unfrozen. For Figure 8, the statement in line 415-416 goes that the IN active site density of the ‘first subpopulation’ (defined by the authors) appears to be higher in both K-rich and Na-rich perthite feldspars compared to those with more balanced Na/K ratios. However, Figure 8a shows that the peak of the ‘first subpopulation’ of IK1 is similar to that of LNaK1 in Figure 8b.

Some data was visualized carelessly. There are some obvious mistakes regarding the labeling in figures and sample/measurement information is inconsistent through the text. For example, the authors introduced sample concentrations in section 2 as ‘concentration of 10, 5, 2, 1, 0.5, 0.1, 0.05, 0.01 and 0.001 wt%.’, however, Figure 3a shows results for samples with concentrations from 5 wt% to 0.00001 wt%. What is the sample with concentration of 0.00001 wt%? And Figure 3b for ns should be based on the frozen fraction data in Figure 3a. But Figure 3a does not include data for a sample with concentration 0.001 wt% which is shown in Figure 3b. And what is the sample called FK1 in Figure 2a? Such a sample is not introduced elsewhere in the main text. We suggest the authors carefully going through the preprint for corrections and ensuring the quality of the presentation.

Discussions on the correlations between sample properties and IN behavior are lacking. The authors first presented the property characterization results for feldspar samples in Figures 1 and 2 and Tables 1 and 2. From Figure 3, the authors started to focus on the IN behavior of the samples. Unfortunately, the authors did not link both parts sufficiently.

The Discussion section is poorly organized. It should be better structured with subtitles and clearer delivery messages.

Some literature citations are inappropriate. For example, line 397 ‘Interestingly, similar trends have been observed in this study (Welti et al., 2019),’. The statement refers to this study, why is there a need to refer to Welti et al. 2019? Also in line 455, one did not see it is necessary to refer to Burrows et al., 2022. The literature is relevant but not cited in the correct way.

Figures generally should be improved for better quality. For example, Figure 1 should have better resolution and Figures 3, 4 and 5 are hard to read because of the poor color scheme.

Given the high sample concentration (1, 2, 5, 10 wt%) tested for droplet freezing experiments, one critical issue would be the aggregation/agglomeration of particles and even the formation of sediment at the tip of PCR wells, which renders the IN results not relevant for suspended particles anymore. Unfortunately, the effects of particle clusters/sediments were not addressed in the preprint. One would challenge that the freezing activity at warm temperatures of concentrated samples is because of freezing on sedimented sample surface, which corresponds to the first sub-group active sites in Figure 8, while the freezing of suspended particles of less concentrated samples at lower temperatures may be more relevant to the second subgroup below -15C. In the literature, it is rarely reported that mineral dust aerosol particles can freeze at such warm temperatures but more reported freezing for T<-15C (Murray et al. 2012) .

We suggest the authors to prepare some text figures and tables in the supplementary. Without any text in the supplementary or if not clearly introduced in the main text like now, it is hard for readers to read them.

Detailed comments:
Line 15: should be ice nucleation

Line 16: ‘comprehensively’ change the wording. One will expect more objective statements. Also for ‘systematically’ (line 430) and ‘robust and statistically meaningful’ (line 431), etc.

Line 17-19: the sample mass concentration should be clarified. Otherwise, the statement is misleading readers to assume K-feldspar is as active as biological particles (e.g., bacteria) that single particles can trigger ice formation at warm sub-zero temperatures.

Line 20: ‘HUB’ should be defined

Line 26: better to use ‘INP parameterizations’ instead of ‘predictive models’

Line 31: should be homogeneous freezing but not homogeneous ice nucleation. Please check Vali et al. (2015).

Line 33: by some of airborne particles. Not all airborne particles are INPs.

Line 41 and 45 (other parts relevant also): be consistent with ‘ice nucleation efficiency’

Line 52: give a definition for active sites. There are already some relevant statements in Line 43-45.

Line 58: ‘specific’? please be explicit and unambiguously develop these statements. Also, there are many statements in this preprint like this in an ambiguous way. Please revise them accordingly.

Line 61-74: consider revising this part and improving Figure 1 with better schematics to more clearly introduce the mineralogy of feldspar

Line 127-128: did the samples for IN measurements undergo the same suspension by sonication?

Line 130: why do the degassing at 393K for 24 hours? There are studies reporting the phase change of feldspar after exposing to temperatures above 100C and leads to increased surface area (e.g., Thomas M. Blattmann, Applied Clay Science 258 (2024) 107477, https://doi.org/10.1016/j.clay.2024.107477).

Line 135: sample concentrations should be consistent with results in following figures

Line 135-136: ‘For each dilution, 96 droplets of 3 μL were dispensed into two 384 -well plates,’ is not a clear statement. How were 96 droplets dispensed into two 384-well plates?

Line 146-147: was background noise subtracted for samples for which there is an influence from the background?

Line 188-190: It is not intuitive to see aligned porosity of samples in the microscopy images. Please indicate it to guide naked eyes.

Line 218-219: NO. Almost all droplets freeze at -20C even for 0.05wt%.

Line 220: should be pure water

Line 226-227: the results of heated samples should be provided, at least in the supplementary

Line 240: equation wrong. Please check Vali (2019) for their equation 4

Line 241: what is N_L(T)? did it show up in equation (1) or somewhere?

Line 247-248: ice nucleation sites

Line 250-254: no discussions on the date in Figure 4. What do we learn from the data? Any deliverables?

Line 267-268: what do we learn from the data? Does it mean the size of particles is not important for feldspar ice nucleation?

Line 276: consistent? How? the data points in Figure 6 spreads for four orders of magnitude around -4C and more than two orders of magnitude at lower temperatures? How can the authors argue that the results are consistent?

Line 290-291: for which sample concentration was the temperature values calculated?

Line 291-292: please indicate the temperature values in many publications the authors referred to. However, in Figure 6, LNaK1 in this study shows the lowest onset temperature, which is lower than results from the literature, isn't it? One cannot write down statements out of the blue.

Line 302-305: we cannot agree. What is the effect of particle agglomeration given such high concentration of particles in the tested samples?

Line 306: now, go back to figure 4. Why not discuss it when first introduce data in Figure 4?

Line 328-329: we cannot agree with the authors that size is not important for particle ice nucleation. Also, BET results depends on particle size. Samples with smaller sizes generally show larger BET surface area. This is also supported by the results of LNa2 (Table 2). The authors should consider this point when discussing results in Figure 5.

Line 334: ‘and correspondingly display higher IN sites densities between −5 to −20 ℃.’ Refers to which figure?

Line 367: Not very similar. The biggest difference is between IK1 and IK2. Any explanations?

Line 391-395: please refer to results presented in figures.

Line 397: It is inapposite to refer to Welti et al. for this study.

Line 406-413: Are these statements relevant to this study? Does this study include any results with samples having different -OH groups?

Line 415-416: over interpretation! The first peak of IK1 is similar to LNaK1 in the figure

Line 419-420: the statement can be supported by results in which figure? Please clearly refer to it

Line 457: which sample group? Be clear

Line 455: why refer to Burrows et al., 2022 when mentioning findings in this study

Technical corrections:
Figure 1: what is Qz? The quality is very poor. Text is hard to read. Is panel a created by the authors or does it need a copyright from other publications?

Table 1: why are sample names in different colors? to highlight anything?

Figure 2: what is the sample FK1 in panel a? According to ACP guidelines, this figure should be labeled as 6 panels. And the font size of the text in the figure should be the same as the main text.

Table 2: the same as for Table 1

Figure 3: Figure 3b should be based on Figure 3a. However, there is no frozen fraction curve for sample with concentration of 0.001wt%. In panel a, the samples with concentration of 0.0001 wt% and 0.00001wt% were not introduced in the main text at all? Where are they from? The color scheme used is a bad decision.

Figure 4: very hard to read because of the bad choice of color scheme

Figure 5: use legend for samples with large and small particles

Figure 6: there are four font sizes in this figure. Please check ACP guidelines

Figure 7: add axis scales. What is the thin black line at the top?

Figure 9: what is the unit on the y-axis for panel b and d?

Figure S4: change the color scheme for better readability

Figure S5: use different colors for better readability

References:
Murray, B. J., O’Sullivan, D., Atkinson, J. D., and Webb, M. E.: Ice Nucleation by Particles Immersed in Supercooled Cloud Droplets, Chem. Soc. Rev., 41, 6519–6554, https://doi.org/10.1039/c2cs35200a, 2012.
Vali, G.: Revisiting the differential freezing nucleus spectra derived from drop-freezing experiments: methods of calculation, applications, and confidence limits, Atmos. Meas. Tech., 12, 1219-1231, https://doi.org/10.5194/amt-12-1219-2019, 2019.
Vali, G., DeMott, P. J., Möhler, O., and Whale, T. F.: Technical Note: A Proposal for Ice Nucleation Terminology, Atmos. Chem. Phys., 15, 10263-10270, https://doi.org/10.5194/acp-15-10263-2015, 2015.

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Citation: https://doi.org/10.5194/egusphere-2025-5014-RC2

Julia Canet, Laura Rodriguez, Galit Renzer, Pura Alfonso, Mischa Bonn, Konrad Meister, Maite Garcia-Valles, and Albert Verdaguer

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https://doi.org/10.5194/egusphere-2025-5014-supplement

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Dataset: Ice nucleation ability of perthite feldspar powder J. Canet et al. https://doi.org/10.5281/zenodo.17396669

Julia Canet, Laura Rodriguez, Galit Renzer, Pura Alfonso, Mischa Bonn, Konrad Meister, Maite Garcia-Valles, and Albert Verdaguer

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Short summary

Alkali-feldspars are known to be efficient ice-nucleating particles. Analysis on the efficiency of perthite feldspars show that it depends on crystallographic structure rather than composition. Microcline-perthites displayed a continuous increase in active site density as temperature was cooled down, while orthoclase showed plateaus, reflecting interruptions in the increase of activity with temperature. These results suggest that order enhances while disorder limits ice nucleation activation.


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