This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Pure water freezes only at around -38°C (-36°F). Tiny mineral dust particles act as so-called ice nucleators—crystallization seeds on which ice crystals form.
A research team at Bielefeld University and the University of Vienna, in cooperation with researchers at the University of Helsinki, has now demonstrated for the first time at the molecular scale why the mineral microcline is particularly effective at forming ice in clouds. The study, published in published in the journal Nature Communications, provides a new explanation for processes that influence climate and precipitation worldwide. The process under investigation helps determine when water in clouds freezes, how much precipitation falls and how strongly clouds reflect sunlight.
All of these factors play a crucial role in the climate. "We wanted to understand why microcline is so exceptionally good at forming ice, even though it differs only slightly in chemical composition from other feldspars, a group of common rock-forming minerals," says Dr. Florian Schneider from Bielefeld University, first author of the study.
"Our results reveal for the first time at the molecular level what makes this mineral so special." Feldspars are among the most abundant minerals in atmospheric dust. Microcline—chemically potassium aluminum silicate—is considered an extremely effective ice nucleator. Until now, researchers assumed that ice forms mainly at rare surface features such as step edges or cracks, so-called active sites.
The research team has now shown that, in the case of microcline, its most common and thermodynamically stable surface—the so-called (001) cleavage plane—is sufficient. Ice grows there in an ordered manner, a process known as epitaxial growth. This means that the crystal lattice of ice aligns at a fixed angle with the crystal lattice of the mineral.
"Interestingly, the (001) surface of microcline does not match the common surfaces of hexagonal ice. Instead, the ice crystals grow with a less common surface, a so-called higher-index plane, aligned to the microcline structure," says Dr. Tobias Dickbreder from the University of Vienna, last author of the study.
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