Polymict

Polymict is an adjective used in geology and meteoritics to describe rocks that contain clasts (fragments) of several different lithologies within a single rock; by contrast, monomict refers to rocks whose clasts come from a single lithology. The term derives from Greek poly- meaning many and mixtus meaning mixed.

In geology, polymict breccias are coarse- to mixed-size rocks composed of angular clasts set in a finer-grained matrix. They form through brecciation due to impacts, tectonic disruption, or rapid sedimentation in partially lithified sequences. The clasts reflect multiple rock types, and the characteristics of the matrix and clasts help interpreters reconstruct the sequence of events that produced the breccia. Polymict breccias are commonly described in regions of impact cratering, fault zones, and other settings where fragmentation and reassembly of rocks occur.

In meteoritics, polymict breccias are meteorites that contain a variety of lithologies within a common matrix, reflecting a history of regolith gardening, fragmentation, and impact processing on the meteorite’s parent body. Such rocks are used to study collisional histories, space weathering, and the architectural diversity of asteroid or planetary surfaces. Polymict materials may include fragments derived from different crustal components and melt-rich clasts formed by impact.

The term polymict is a descriptive label applied to rocks and meteorites that record multiple lithologies and formation pathways, rather than a strict taxonomic category. It is commonly encountered in rock descriptions and classification discussions, particularly for breccias.