Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. Phosphorus is also known as diphosphorus (P), an unstable diatomic allotrope. Hexagonal graphitic carbon (graphite) is the most thermodynamically stable allotrope of carbon under ambient conditions. Graphene is a crystalline allotrope of carbon with 2-dimensional properties. Black phosphorus is the least reactive allotrope and the thermodynamically stable form below . Phosphorene is a 2-dimensional, crystalline allotrope of phosphorus. Graphyne is another 2-dimensional carbon allotrope whose structure is similar to graphene's. Graphite is the most stable allotrope of carbon. However, the alpha allotrope is diamagnetic. The yellow allotrope of antimony is the most unstable. Graphene has the highest ratio of edge atoms of any allotrope. Examples of solid elemental insulators are diamond (an allotrope of carbon) and sulfur. The synthesis of an orthorhombic allotrope Si, was subsequently reported in 2014. Amorphous carbon is a third allotrope of carbon; it is a component of soot. Diamond is a well known allotrope of carbon.