Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar
- Author(s)
- Alexei A. Kiselev, Alice Keinert, Tilia Gaedeke, Thomas Leisner, Christoph Sutter, Elena Petrishcheva, Rainer Abart
- Abstract
Feldspar is an important constituent of airborne mineral dust. Some alkali feldspars exhibit particularly high ice nucleation (IN) activity. This has been related to structural similarities of the ice (10 (1) over bar0) prism planes and the (100) planes of alkali feldspar. Here the effect of generating feldspar surfaces with close to (100) orientation by means of chemically induced fracturing on the IN activity of alkali feldspar was investigated experimentally. To this end, gem-quality K-rich alkali feldspar was shifted towards more Na-rich compositions by cation exchange with an NaCl-KCl salt melt at 850 degrees C. By this procedure, a system of parallel cracks with an orientation close to the (100) plane of the feldspar was induced. Droplet-freezing assay experiments performed on grain mounts of the cation-exchanged alkali feldspars revealed an increase in the overall density of icenucleating active site (INAS) density with respect to the untreated feldspar. In addition, annealing at 550 degrees C subsequent to primary cation exchange further enhanced the INAS density and led to IN activity at exceptionally high temperatures. Although very efficient in experiment, fracturing by cation exchange with an alkali halide salt is unlikely to be of relevance in the conditioning of alkali feldspars in nature. However, parting planes with similar orientation as the chemically induced cracks may be generated in lamellar microstructures resulting from the exsolution of initially homogeneous alkali feldspar, a widespread phenomenon in natural alkali feldspar known as perthite formation. Perthitic alkali feldspars indeed show the highest IN activity. We tentatively ascribe this phenomenon to the preferential exposure of feldspar crystal surfaces oriented sub-parallel to (100).
- Organisation(s)
- Department of Lithospheric Research
- External organisation(s)
- Karlsruher Institut für Technologie, Scientific Software Center
- Journal
- Atmospheric Chemistry and Physics
- Volume
- 21
- Pages
- 11801-11814
- No. of pages
- 14
- ISSN
- 1680-7316
- DOI
- https://doi.org/10.5194/acp-21-11801-2021
- Publication date
- 08-2021
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105105 Geochemistry, 105120 Petrology
- Keywords
- ASJC Scopus subject areas
- Atmospheric Science
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/dd9c1f64-875f-4867-817e-ceefde9850b7