the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Oct 2025
Measurement report: Ice nucleation ability of perthite feldspar powder
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.
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Status: open (until 07 Dec 2025)
- RC1: 'Comment on egusphere-2025-5014', Thomas F. Whale, 07 Nov 2025 reply
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Dataset: Ice nucleation ability of perthite feldspar powder J. Canet et al. https://doi.org/10.5281/zenodo.17396669
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- 1
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.