Pigeonite

Pigeonite is a monoclinic clinopyroxene mineral in the pyroxene group. It is commonly described as a low-calcium member of the augite group, with a composition that is broadly written as (Ca,Mg,Fe)Si2O6. Pigeonite forms a solid solution with other clinopyroxenes, and lies between diopside-hedenbergite and enstatite in terms of calcium content and iron-magnesium balance. Its crystal structure and chemistry reflect high-temperature stability in basaltic to gabbroic systems.

In geological settings, pigeonite occurs in mafic and ultramafic rocks and is also found in meteorites, including some eucrites and howardites. It crystallizes at high temperatures during the early stages of basaltic magmatism and can be preserved in rapidly cooled rocks. On slower cooling, pigeonite commonly exsolves to intergrowths of augite and enstatite, producing characteristic lamellar textures that are visible under an optical microscope.

Physically, pigeonite typically appears as greenish to brownish-gray crystals and shows two good cleavages. It is identified in hand samples and thin sections by its prismatic habit, monoclinic symmetry, and distinctive exsolution textures. In petrology and meteoritics, pigeonite serves as a diagnostic mineral for deciphering magmatic processes, cooling histories, and the thermal evolution of planetary materials.