Oheimnum

Oheimnum is a hypothetical silicate mineral used in theoretical discussions of high-pressure geology and in science fiction to illustrate mineral stability under extreme conditions. In speculative models, it is described as forming in ultra-high-pressure metamorphic environments and possessing a three-dimensionally connected framework of tetrahedrally coordinated cations that accommodates substantial chemical substitutions.

Composition and structure are described in approximate terms rather than a fixed chemical formula. Oheimnum is often depicted as an aluminosilicate with moderate transition-metal substitution, commonly represented with substitutions of Al, Fe, Ti, and Cr in framework sites and interstitial cations occupying remaining coordination sites. This variability is intended to reflect natural substitutions seen in complex mantle and crustal minerals, while preserving a distinctive lattice that supports anisotropic properties.

Physical properties attributed to oheimnum in its fictional context include a high refractive index and notable optical anisotropy under polarized light. Reported hardness ranges from around 6 to 7 on the Mohs scale, with a vitreous to subadamantine luster and a density estimated near 3.8 g/cm3, dependent on substitution levels. Color is described as deep amber to reddish-brown in illustrative specimens.

Occurrence and formation are placed in subduction-zone or deep crustal metamorphic settings under temperatures oriented toward 800–1200°C and high pressures. No natural specimens have been confirmed, and oheimnum is not recognized by the International Mineralogical Association. It remains a pedagogical tool for discussing high-pressure mineralogy and substitution chemistry in teaching and speculative literature.