Melteigites

Melteigites are a type of igneous rock, specifically a feldspathoid-bearing rock. They are characterized by the presence of melilite and clinopyroxene as essential minerals, with melilite being a solid solution series between the minerals åkermanite and gehlenite. In addition to these primary minerals, melteigites may also contain nepheline, alkali feldspar, perovskite, and various spinels. They are typically dark-colored, fine-grained, and dense.

These rocks are considered undersaturated with silica, meaning they contain minerals that form in the absence of free quartz. This undersaturation is a key characteristic that distinguishes them from other igneous rock types. Melteigites are relatively rare and are most commonly found in association with other melilite-bearing rocks, such as melilite basalt or uncompahgrite, often within alkaline intrusive complexes or as components of volcanic flows.

The formation of melteigites is thought to occur at relatively low pressures and high temperatures, typical of deep crustal or upper mantle environments. Their occurrence is often linked to magmatic processes involving the melting of mantle peridotite that has been metasomatized by carbonatitic or alkali-rich fluids. Study of melteigites can provide insights into the composition of the Earth's mantle and the processes of alkaline magmatism.