melilitite

Melilitite is a rare igneous rock that is ultramafic and alkaline in composition. It is characterized by the presence of melilite, a solid solution series of minerals belonging to the melilite group, which typically includes åkermanite and gehlenite. Melilitite is found in a variety of geological settings, often associated with alkaline igneous provinces and carbonatites. These rocks are typically dark-colored due to their high content of mafic minerals.

The mineral melilite itself is a calcium magnesium silicate with the general formula (Ca,Na)2(Mg,Fe2+,Al)(Si,Al)2O7. Its exact composition can vary, influencing the overall properties of the melilitite rock. Other common minerals found in melilitite include perovskite, magnetite, nepheline, and various pyroxenes. The rarity of melilitite is partly due to the relatively unstable nature of melilite under typical surface conditions, where it tends to alter.

Geologically, melilitites are considered to be derived from deep within the Earth's mantle, often from low-degree partial melting events. They are found in association with other alkaline rocks such as nephelinites and basanites, and sometimes in xenoliths within kimberlites. The occurrence of melilitite is geographically widespread but occurs in localized occurrences, with notable examples found in regions like the Italian Alps, Germany, and parts of Africa and North America. Studying melilitite provides valuable insights into the composition and processes occurring in the Earth's upper mantle.

---