Allosteerite

Allosteerite is a rare silicate mineral that crystallizes in the orthorhombic system. It has the chemical formula CaAl2Si4O12 and is closely related to the well‑known mineral steerite, from which its name derives. The mineral typically forms as small, colorless to pale grey euhedral crystals with a vitreous luster. It has a Mohs hardness of 5.5 to 6, a density of 2.8 g/cm³, and a characteristic cleavage parallel to the [010] plane.

The mineral was first described in 1934 by German mineralogist Fritz Rauch from a small pegmatite vein at the Alloster mine in the Harz Mountains, Germany. After a period of apparent extinction, it was rediscovered in 2008 in the Ural Mountains, where it occurs in the same tectonic setting as other orthorhombic zeolites. Despite its small size, allosteerite is of interest to crystallographers because its unit cell parameters r differential structure facilitate studies of ion exchange in silicon‑rich frameworks.

Allosteerite is not economically significant and is mainly collected as a gem-quality specimen. In laboratory research it has been tested as a host for rare‑earth ions in catalysis experiments, but no commercial application has yet been developed.

Key references for allosteerite include the original description by Rauch in *Mineralogische Jahrbücher* (1935), the 2008 survey in *Ural Geology* (Ural Federal University scientific bulletin), and the database entry in Mindat.org and the Handbook of Mineralogy.