Kirschsteinite (mainly CaFeSiO4), in association with forsterite-fayalite solid solutions, melilite, clinopyroxene, leucite, nepheline and several minor phases, is reported for the first time in the 290 ka Capo di Bove melilite-leucitite lava flow of the Alban Hills volcanic complex (Italy). Kirschsteinite appears very late in the crystallization sequence, as indicated by textural and chemical evidence (Mg# ≈ 25). It shows significant solid solution towards fayalite, and is found with groundmass phases indicating a relatively low-temperature melt composition more silica-undersaturated than phonolite (i.e. devoid of alkali feldspar). This clearly points to the very silica-undersaturated nature of almost all the Alban Hills volcanic rocks.
