 Ca3P2 is a new high-temperature form of this material, which has a unique crystal structure consisting of a hexagonal Mn5C3 type with a Caion deficiency. This results in a stable, charge-balanced compound of Ca2 plus and P3 minus. Additionally, we observed a secondary hydride phase, Ca5P3H, which is also charge-balanced. Ca3P2 is a three-dimensional Dirac semi-metal with a highly unusual ring of Dirac nodes at the Fermi level, which is protected from gap opening by a mirror plane. This article was authored by Lilia S. Sia, Leslie M. Scope, Elizabeth M. Seibel, and others.