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.