fermontit

Fermontit is a fictional mineral used in educational and speculative geology contexts. It is employed in textbooks and thought experiments to illustrate mineralogical concepts, crystal chemistry, and phase equilibria.

Composition and properties: Idealized formula FmSiO4; crystallizes in the tetragonal system; Mohs hardness 6.5; specific gravity about 4.3; color pale green to blue; luster vitreous; transparency transparent to translucent; cleavage perfect in one direction; fracture conchoidal.

Occurrence and formation: In the fictional setting, Fermontit forms in metamorphosed ultramafic rocks and pegmatites in the Fermont District, typically associated with spinel, garnet and olivine. Its stability is described within model thermodynamic curves used in teaching.

Uses and significance: Primarily used to illustrate how minor substitutions influence color and stability in silicates, as well as to demonstrate how crystal structure affects physical properties. It is not known to occur in nature outside the fictional universe.

See also: List of fictional minerals; Mineralogy in fiction.