Back in 1935, Eugene Wigner and Hillard Huntington predicted that under high enough pressures solid hydrogen would become metallic, with properties similar to the alkali metals (superconductor and an effective and clean rocket propellant (2,4). In addition, understanding metallic hydrogen could be important for improving energy yields from nuclear fusion, since the nuclei would be closer [...]

The element sulfur is found in the form of several allotropes, two of which, monoclinic and rhombic sulfur, are shown below.
Left: Rhombic sulfur (Courtesy of Ken O’Donoghue), Right: Monoclinic sulfur [...]