Pigeonite

Pigeonite is a calcium-poor clinopyroxene with magnesium and iron occupying key crystal sites. It occurs in some volcanic rocks, plutonic rocks, and meteorites.

Pyroxene: A group of inosilicate minerals built from single chains of linked silica tetrahedra. Pigeonite is one member of this mineral group.
Pyroxene quadrilateral: A compositional diagram showing relations among major magnesium-, iron-, and calcium-rich pyroxenes. It locates pigeonite within the principal pyroxene compositional system.
Basalt: A fine-grained mafic igneous rock formed when low-silica magma cools at or near the surface. Pigeonite occurs in some basalts and helps characterize their crystallization history.
Tholeiitic basalt: A basalt produced by a tholeiitic magma series, commonly associated with iron enrichment during differentiation. Pigeonite can crystallize in tholeiitic basaltic magmas.
Clinopyroxene: A pyroxene subgroup whose crystals have monoclinic symmetry. Pigeonite belongs to this structural subgroup.
Exsolution: The separation of a once-uniform solid solution into distinct mineral phases during cooling or changing conditions. Cooling can separate pigeonite into finer pyroxene lamellae.
Achondrite: A stony meteorite that experienced melting or igneous differentiation on its parent body. Pigeonite occurs in several achondrites, recording extraterrestrial magmatic processes.
Lunar basalt: A basaltic rock formed by volcanic activity on the Moon. Pigeonite-bearing assemblages occur in some lunar basalts.
Silicate minerals: Minerals whose structures contain silicon–oxygen tetrahedra as a fundamental building block. Pigeonite’s silicate chains define its basic mineral structure.
Inversion (mineralogy): A change in a mineral’s crystal structure without a change in its chemical composition. Pigeonite can transform to orthopyroxene as it cools.

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