duulis

Duulis is a rare and distinctive mineral species, first discovered in 1983 in the Khibina Massif, Kola Peninsula, Russia. It is a complex sodium-calcium-silicate with the chemical formula Na2Ca2Si8O20. Duulis crystallizes in the monoclinic system and typically forms prismatic crystals, although it can also occur as granular masses. The mineral is usually colorless or white, but can exhibit a faint pinkish tint due to the presence of trace amounts of iron.

Duulis is notable for its unique crystal structure, which is characterized by the presence of eight-membered rings of silica tetrahedra. This structure is distinct from that of other known silicate minerals. The mineral is also notable for its occurrence in the alkaline igneous rocks of the Khibina Massif, where it is associated with minerals such as nepheline, sodalite, and eudialyte.

Duulis is a relatively rare mineral, and specimens are sought after by collectors due to their distinctive crystal habit and unique chemical composition. However, due to its rarity and the difficulty of its synthesis, duulis is not commonly used in industrial applications. Instead, it is primarily of interest to mineralogists and collectors.