Helifailide

Helifailide is a fictional mineral term commonly used in speculative geology and science fiction to describe a hypothetical ore that forms in sunlit environments, such as the near-surface crusts of tidally locked exoplanets or planets with extreme insolation.

The name blends heli- from the Greek for sun with a fictional mineral suffix used in some works.

In most depictions helifailide is a dense, metallic-looking mineral with a dark luster and a submetallic or adamantine sheen. Reported densities vary; hardness on the Mohs scale is described between 4 and 7. It is sometimes described as having luminescent properties under ultraviolet light and as being brittle, with a tabular or acicular crystal habit in speculative models.

In fiction, helifailide is said to form through solar-irradiation-driven metasomatism, high-temperature crystallization in lava tubes under intense insolation, or as a product of solar wind implantation and metamictization. There are no verified natural samples; no peer-reviewed analyses exist.

In stories, it is valued as a source of energy or as a catalyst in hypothetical fusion or photonic devices; its properties and value differ between works.

Related terms include fictional minerals and speculative geology concepts.