Viljumine

Viljumine is a rare silicate mineral first described in the Vilju region of Norda in 1994. It is part of the feldspathoid-silicate family and is characterized by a complex, variable composition that permits a range of cations, notably iron and magnesium, in its crystal lattice. The name derives from Vilju, the site of its discovery, with the suffix -mine a conventional mineral-name ending.

Chemical composition and crystal structure: Viljumine typically lacks a fixed empirical formula due to extensive cation substitution, particularly among iron, magnesium, calcium and aluminum. It is commonly described as monoclinic with a layered crystal framework. Major constituents are iron, magnesium, calcium and aluminum, with trace vanadium and titanium. It forms prismatic crystals and foliated masses, often displaying a vitreous to resinous luster; color ranges from olive-green to brown.

Occurrence and formation: Found in hydrothermally altered granitic rocks and high-silica veins, Viljumine develops at moderate temperatures and low pressures during late-stage hydrothermal activity. It is frequently associated with quartz, muscovite, magnetite and apatite.

Mining and use: Due to its rarity, Viljumine has limited industrial use; it is primarily of interest to mineral collectors and researchers studying silicate structures. Analytical studies focus on its crystal chemistry and solid-solution behavior under varying redox conditions.