leucitite

Leucitite is a rare igneous rock, specifically a type of volcanic rock, that is characterized by its high content of leucite, a mineral with the chemical formula KAlSi2O6. Leucite is a feldspathoid mineral, meaning it is structurally related to feldspar but deficient in silica. This silica deficiency is a key characteristic of leucitite, as it forms in magmas with a low silica content. Leucitites are typically dark-colored, fine-grained rocks, often appearing glassy or porphyritic. They are generally found in association with alkaline volcanic provinces, particularly those of continental rift zones and some oceanic islands.

The mineral composition of leucitite includes leucite as the dominant feldspathoid mineral, along with a significant amount of alkali feldspar (often anorthoclase or sanidine) and clinopyroxene (such as augite). Other accessory minerals may include olivine, biotite, and magnetite. Due to the scarcity of silica in their parent magma, quartz is never present in leucitites. The texture can vary, but often shows large leucite crystals embedded in a finer-grained groundmass. Leucitites are rare globally, with notable occurrences in regions like Italy (e.g., the Roman volcanic province), Uganda, and parts of North America. Their study provides insights into the petrogenesis of silica-undersaturated alkaline magmas and the geological conditions under which they form.