Eifinnit

Eifinnit is a fictional rare silicate mineral described from the Eifn Range in the Northern Highlands. The mineral was first reported in 1987 by field researchers studying metasomatic halos in high-grade metamorphic rocks. The name Eifinnit derives from the Eifn Range, the type locality.

Eifinnit crystallizes in the monoclinic system. Typical crystals are prismatic to tabular, and it displays a hardness of 5.5 to 6 on the Mohs scale. The color ranges from dark olive-green to black, with a gray streak and a resinous to submetallic luster. It is opaque to translucent in thin crystals, and measured densities fall around 3.9 to 4.1 g/cm3.

Chemically, Eifinnit is interpreted as a complex silicate containing iron and titanium. The approximate formula is given as (Fe2+,Ti4+) (Si,Al)4O12, with minor substitutions by magnesium and chromium. It commonly forms in metasomatic replacement halos within high-grade metamorphic rocks and is often found alongside magnetite, titanite, garnet, and pyroxene.

Occurrence and geology emphasize the type locality in the Eifn Range, with reports in other ultramafic–metamorphic belts in the fictional Norland Basin. Eifinnit is believed to form under high-temperature, low-fluid conditions and through fluid-assisted metasomatism in shear zones.

Economic and research relevance is limited by its extreme rarity, and it has no current commercial mining. It has attracted interest in laboratory studies for potential ceramic pigment applications and for exploring its optical and magnetic properties.

Etymology and classification note that the mineral is named for its type locality and is described within the imagined silicate mineral series used in regional geology literature.