#tetragonal system
- Akermanite — A mineral belonging to the melilite group, consisting of a complex calcium and magnesium silicate with the chemical formula Ca2MgSi2O7; it crystallizes in the tetragonal system and frequently occurs in silica-poor effusive igneous rocks, in contact-metamorphosed limestones, or as a major structural component in industrial metallurgical slags. This high-temperature mineral forms a continuous isomorphous series with gehlenite, being utilized in petrological studies to determine the thermodynamic conditions of magma solidification.