hexaferrum

Hexaferrum is a term that appears in some historical, speculative, or fictional contexts to denote a hexagonal form of iron or a hypothetical hexagonal allotrope. It is not an officially recognized name for any iron phase and is not listed by major standards bodies such as IUPAC. The label combines ferrum, the Latin word for iron, with hex-, indicating hexagonal symmetry or structure.

In established iron chemistry and metallurgy, the stable form of iron at ambient conditions is body-centered cubic (bcc) alpha-iron. At higher temperatures, iron can adopt a face-centered cubic (fcc) gamma-iron, and under other high-temperature or high-pressure conditions other phases such as delta-iron (bcc) or, in some high-pressure studies, a hexagonal close-packed form (often referred to as hexagonal iron or epsilon-iron) have been discussed. The hexagonal phase is typically treated separately from the informal term hexaferrum, and its existence and properties vary across studies and theoretical predictions.

In fiction and popular science, hexaferrum may be used as the name of a fictional element or material with extraordinary properties. It should not be confused with hexaferrites, which are a real class of magnetic ceramic compounds (for example BaFe12O19, SrFe12O19) used in permanent magnets.

Because usage of the term is inconsistent, readers should rely on context to determine whether hexaferrum refers to a speculative hexagonal iron phase or to a fictional material.