Scientists have demonstrated that supercompressed water transforms into ice VI at room temperature through multiple freezing-melting pathways, which occur via a previously unknown form of metastable ice, named ice XXI. A small crystal of ice XXI formed through nucleation and slow melting process. Image credit: Lee et al., doi: 10.1038/s41563-025-02364-x. Water, composed of only two elements, forms numerous polymorphic phases from ice Ih to ice XX...
