Alulleen

Alulleen is a hypothetical lithium aluminum silicate mineral described for use in mineralogical case studies. It is said to have been first described from pegmatite pockets in the fictional Alulleen region and is named after the local term alulleen, meaning bright stone. For purposes of this article, it is treated as a distinct mineral species.

Its idealized chemical composition is LiAlSi2O6, with substitutions by Mg2+, Fe2+, and Na+ in the crystal structure; trace amounts of Ti and Cr may occur.

Alulleen crystallizes in the monoclinic system and forms prismatic to tabular crystals. It is typically pale yellow to green in color, with a white streak, a vitreous luster, and a transparent to translucent appearance. The Mohs hardness is about 5.5 to 6.

It occurs in late-stage pegmatites and metasomatic halos within alkaline igneous rocks, and is commonly associated with other lithium-bearing minerals such as spodumene and petalite, as well as beryl and quartz.

The name derives from the local language term alulleen, meaning bright stone, and the species is presented here as a model for nomenclature and classification discussions.

Because of its lithium content, alulleen has been considered as a potential lithium ore on a purely hypothetical basis, but its rarity and restricted locality limit practical exploitation. It is studied mainly for crystal-chemical behavior and as a teaching example in mineral classification.