(Karlsruher Institut für Technologie (KIT) ) In the atmosphere, feldspar particles act as ice nuclei that make ice crystals grow in clouds and enable precipitation. The reason was found by researchers of Karlsruhe Institute of Technology (KIT) and University College London (UCL) with the help of electron microscopy observations and molecular dynamics computer modeling. The ice nucleus proper is a quasi-hidden crystal surface of the feldspar that is exposed at surface defects only. The researchers present their findings in Science.