surfaces yielded ice with as little strain as this
feldspar (100)/ice ð101 −0Þ interface.
Two aspects of the results are worth elaborating in more detail. First, contrary to the often
implicitly made assumption that in the case of
epitaxial growth, ice nucleates from the basal
face, our results suggest that this does not happen on K-feldspar. Basal plane epitaxy was most
often observed in the experiments with synthetic
and natural substrates (21, 22, 49). However, nucleation of the prism plane on a substrate is
not unknown (21). Several molecular dynamics
studies have also found nucleation of a prism
face aligned with the basal face of clay minerals
Second, as shown in Fig. 5, the interaction
between feldspar and water is indeed mediated
by hydroxyl groups on the feldspar surface. The
prism face grows directly on the hydroxylated
(100) feldspar surface, in contrast to the predictions of ice growth on the (001) surface, where a
non–ice-like layer mediates the structure between ice and the substrate (43). This suggests
that surface OH groups play an important role
in the ice nucleation process, by allowing ice-like structures to form even without an apparent epitaxial match. Thus, it is not surprising that
affecting the OH arrangement by natural weathering or chemical treatment affects the ice nucleation process, as discussed further in the
supplementary materials. The role of OH groups
might provide a clue for understanding the observed strong variability of ice nucleation effi-cacies of various feldspars (10, 40) because the
natural variability of lattice constants, microtex-ture, heterogeneity of Al:Si ratio, and so forth
will be reflected in the ordering of the surface
hydroxyl groups, thus affecting the ability of
feldspar dust particles to serve as IN particles.
We hypothesize that the affinity of feldspar
(100) patches for ice, as described in this study,
should be universal for both deposition and im-
mersion modes of heterogeneous ice nucleation.
In both regimes, the ability of the active site to
reduce the energy of nucleus formation defines
the ice nucleation efficiency of a substrate. In
both regimes, the energy of the nucleus-substrate
interface must be the same. What is different,
however, is the flux of water molecules toward
the critical nucleus and the surface tension of
the nucleus, and therefore its size. We argue that
the ability of (100) surface patch to bind a certain
crystal plane of ice (prism) should be relevant in
immersion freezing as well as in deposition ice
nucleation, leading to acceleration of the nucle-
ation rate. The ice nucleation onset conditions,
as well as the observable features (habit and ori-
entation of ice crystals), will, of course, be dif-
ferent for different nucleation modes.
In this study, we have experimentally identified the IN active sites on the surface of K-rich
feldspar as the surface patches with (100) crystallographic orientation. These patches occur
exclusively at surface features like steps, cracks,
and cavities that arise during fracturing processes (such as grinding or mechanical weathering). The preferential nucleation of ice on the
defects is dominated by the presence of these
patches. This finding will help to characterize the
IN properties of natural mineral dust aerosol
particles, which almost universally contain feldspar. The feldspar particles with the highest
density of specific crystal planes exposed in the
surface defects should constitute the most efficient IN particles. Moreover, aided by atomistic
computer simulations, we showed that on these
patches, hydroxyl groups mediate the interaction
between ice and feldspar. These observations
constitute direct identification of an IN surface
site on an inorganic substrate at the molecular
level. The nucleation of nonbasal faces of ice on
surfaces with relatively high surface free energy,
which are not expressed as dominant surface
facets, could be relevant to ice formation on other
mineral dusts and substrates.
REFERENCES AND NOTES
1. T. W. Wilson et al., Nature 525, 234–238 (2015).
2. J. D. Atkinson et al., Nature 498, 355–358 (2013).
3. N. Hiranuma et al., Nat. Geosci. 8, 273–277 (2015).
4. M. A. Freedman, J. Phys. Chem. Lett. 6, 3850–3858 (2015).
5. N. Hiranuma et al., Atmos. Chem. Phys. 14, 13145–13158
6. C. Hoose, O. Möhler, Atmos. Chem. Phys. 12, 9817–9854
7. B. J. Murray, D. O’Sullivan, J. D. Atkinson, M. E. Webb,
Chem. Soc. Rev. 41, 6519–6554 (2012).
8. J. D. Yakobi-Hancock, L. A. Ladino, J. P. D. Abbatt,
Atmos. Chem. Phys. 13, 11175–11185 (2013).
9. G. P. Schill, K. Genareau, M. A. Tolbert, Atmos. Chem. Phys. 15,
10. A. D. Harrison et al., Atmos. Chem. Phys. 16, 10927–10940
11. A. Hodgson, S. Haq, Surf. Sci. Rep. 64, 381–451 (2009).
12. J. Carrasco, A. Hodgson, A. Michaelides, Nat. Mater. 11,
13. N. H. Fletcher, J. Atmos. Sci. 26, 1266–1271 (1969).
14. N. H. Fletcher, Aust. J. Phys. 13, 408–418 (1960).
15. P. J. Connolly et al., Atmos. Chem. Phys. 9, 2805–2824
16. W. Cantrell, A. Heymsfield, Bull. Am. Meteorol. Soc. 86,
17. H. R. Pruppacher, J. D. Klett, Microphysics of Clouds and
Precipitation (Kluwer Academic Publishers, ed. 2, 2004).
18. G. Vali, Molecules 1999, 1–22 (1999).
19. S. J. Cox, Z. Raza, S. M. Kathmann, B. Slater, A. Michaelides,
Faraday Discuss. 167, 389–403 (2013).
20. M. Fitzner, G. C. Sosso, S. J. Cox, A. Michaelides, J. Am.
Chem. Soc. 137, 13658–13669 (2015).
21. G. W. Bryant, J. Hallett, B. J. Mason, J. Phys. Chem. Solids 12,
22. J. L. Caslavsky, K. Vedam, J. Appl. Phys. 42, 516–520 (1971).
23. N. Cho, J. Hallett, J. Cryst. Growth 69, 317– 324 (1984).
24. T. Kobayashi, Contrib. from Inst. Low Temp. Sci. A20, 1–22
25. B. Vonnegut, J. Appl. Phys. 18, 593–595 (1947).
26. D. Turnbull, B. Vonnegut, Ind. Eng. Chem. 44, 1292–1298
27. T. Croteau, A. K. Bertram, G. N. Patey, J. Phys. Chem. A 112,
28. T. Croteau, A. K. Bertram, G. N. Patey, J. Phys. Chem. A 113,
29. X. L. Hu, A. Michaelides, Surf. Sci. 601, 5378–5381 (2007).
30. X. L. Hu, A. Michaelides, Surf. Sci. 602, 960–974 (2008).
31. S. A. Zielke, A. K. Bertram, G. N. Patey, J. Phys. Chem. B 120,
32. H. K. Christenson, CrystEngComm 15, 2030 (2013).
33. C. Marcolli, Atmos. Chem. Phys. 14, 2071–2104 (2014).
34. B. Federer, Z. Angew. Math. Phys. 19, 637–665 (1968).
35. J. Hallett, S. K. Shrivastava, J. Rech. Atmos. 5, 223–236
36. B. J. Anderson, J. Hallett, J. Atmos. Sci. 33, 822–832 (1976).
37. S. J. Cox, S. M. Kathmann, J. A. Purton, M. J. Gillan,
A. Michaelides, Phys. Chem. Chem. Phys. 14, 7944–7949
38. L. Lupi, V. Molinero, J. Phys. Chem. A 118, 7330–7337 (2014).
39. L. Lupi, A. Hudait, V. Molinero, J. Am. Chem. Soc. 136,
40. A. Peckhaus, A. Kiselev, T. Hiron, M. Ebert, T. Leisner,
Atmos. Chem. Phys. 16, 11477–11496 (2016).
41. J. V. Smith, Feldspar Minerals 2 Chemical and Textural
Properties (Springer, Berlin, Heidelberg, ed. 1, 1974).
42. K. G. Libbrecht, Proc. R. Soc. London 49, 323–343 (2012).
43. P. Pedevilla, S. J. Cox, B. Slater, A. Michaelides, J. Phys. Chem.
C 120, 6704–6713 (2016).
44. I. Parsons, Ed., Feldspars and Their Reactions (Kluwer
Academic Publishers, Series C, 1994), vol. 421.
45. J. V. Smith, Proc. Natl. Acad. Sci. U.S.A. 95, 3366–3369
46. H. Behrens, Mineral. Mag. 59, 15–24 (1995).
47. R. T. Cygan, J.-J. Liang, A. G. Kalinichev, J. Phys. Chem. B 108,
48. H. J. C. Berendsen, J. P. M. Postma, W. F. van Gunsteren,
J. Hermans, in Intermolecular Forces, B. Pullman, Ed.
(Springer Netherlands, 1981), pp. 331–342.
49. N. Fukuta, B. Mason, J. Phys. Chem. Solids 24, 715–718 (1963).
The preparation and x-ray diffraction characterization of feldspar
samples at the Institute of Applied Geosciences of TU Darmstadt
(M. Ebert) as a part of cooperation within the Deutsche
Forschungsgemeinschaft (DFG)–funded research unit INUIT
(DFG-FOR-1525-6343) is greatly acknowledged. This work
was also partly supported by KIT Startup Budget 2011
370 27 JANUARY 2017 • VOL 355 ISSUE 6323 sciencemag.org SCIENCE
Fig. 5. The most stable structure of ice on feldspar (100) found in force field simulations. (A and
B) Side views. (C) Top view. Ice Ih is attached with its primary prism plane (1010) to the (100) face of
feldspar. Colors of tetrahedra are the same as in Fig. 1. Oxygen and hydrogen atoms in ice are shown in
red and gray, respectively. In the top view (C), the feldspar underlying structure is shown in pale colors.
The primitive feldspar (100) slab unit cell (orthogonal) used in the simulations is shown as the open red
box, whereas the axes show the directional vectors of an ideal monoclinic feldspar unit cell.