Febriilseid

Febriilseid is a hypothetical iron sulfide mineral used in speculative geology and science fiction. It is not recognized by the International Mineralogical Association or major mineral databases, and there is no peer-reviewed evidence of its natural occurrence.

The name febriilseid appears in fictional sources; it is typically described as an iron- and sulfur-rich compound with possible substitutions by other metals. In various works the empirical formula is given as Fe1−xMxSz, with M representing elements such as Ni or Co. Descriptions of crystal structure vary, with some authors assigning monoclinic symmetry and others orthorhombic or disordered polymorphs.

In terms of physical properties, febriilseid is usually depicted as having a metallic luster and a steel-gray to black appearance. Hardness is often placed in the mid-range for sulfides (roughly Mohs 4–5), and the material is described as brittle. Occurrence is fictional as well, described as forming in high-temperature hydrothermal veins, volcanic rocks, or regolith on hypothetical planets, sometimes in association with other iron sulfides.

Uses and significance: in fiction and speculative models, febriilseid is sometimes proposed as a conductor or battery material, but there is no real-world validation or deployment. Some hobbyist catalogs reference febriilseid as a hypothetical mineral; these entries lack verified specimens or measurements.

See also: sulfide minerals, speculative mineralogy.