Ice nucleation on microcline (001) in the absence of active sites

Heterogeneous ice nucleation is at the heart of a wide range of technological and natural fields ranging from cryopreservation ¹ and the development of anti-icing coatings ^2–4 to the glaciation of clouds ^5–11 . The latter process has a profound impact on Earth’s climate as it changes major physical properties, such as the albedo and precipitation efficiency ^6,7 . Of the many different ice-nucleating mineral particles, dust from feldspar mineral microcline stands out as being particularly active ^11–17 . However, why microcline outperforms other particles remains a puzzle. Here, we use nanoscale imaging to show that the (001) surface of microcline is able to induce ice nucleation in the absence of active sites. In contrast, for the closely related feldspar sanidine, ice nucleation is dominant at step edges as expected. Atomistic simulations suggest that the ice nucleation is induced by a lattice match between the higher index (10.4) plane of hexagonal ice and microcline. Our findings provide a nanoscopic explanation for microcline’s exceptional ice nucleation ability and demonstrate the importance of taking higher-index surfaces into account. We expect that the latter insight will enhance our understanding of nucleation processes in nature and our ability to create materials with outstanding ice nucleating abilities.