Järeliide

Järeliide is a rare mineral in the silicate group, first described from high-grade metamorphic rocks in the Järeli region. The type material was reported in 2012 by researchers from the University of Tartu and the Estonian Geological Survey. The name derives from the locality; the suffix -ide is standard for minerals.

Composition and structure: Järeliide represents a complex silicate with a variable composition in a solid-solution series. Its framework comprises silicon-oxygen tetrahedra with metal cations, commonly iron, magnesium and aluminium, in octahedral sites, and trace rare earth elements. Exact formulas vary, described empirically rather than by fixed stoichiometry.

Physical properties: Crystallizes in the monoclinic system and forms pale silvery gray to greenish-brown prismatic crystals. Mohs hardness about 5.5–6; vitreous luster; gray streak; cleavage weak or absent; density 3.3–3.6 g/cm3. Crystals are generally small and often translucent in fine specimens.

Occurrence: The type locality is the Järeli quarry in northern Europe, where Järeliide occurs in high-temperature metamorphic rocks and late-stage hydrothermal veins. It is commonly found with quartz, cordierite, sillimanite and magnetite, reflecting formation under granulite-facies conditions with limited fluid activity.

Classification and status: Järeliide is regarded as a rare mineral of scientific interest with no commercial use due to scarcity. It contributes to understanding silicate structures in metamorphic rocks. The International Mineralogical Association approved the name in 2016, and ongoing study examines its solid-solution behavior.