Impactites

Impactites are rocks formed by the energy of a meteorite or comet impact with a planetary surface. They include materials melted, vaporized, fractured, or redeposited by the shock wave of an impact, and later cooled, cemented, or brecciated within the crater or ejecta blanket. The term covers a range of rock types, from glassy melts to breccias and melt-rich rocks, and it distinguishes these rocks from the impactors themselves.

Tektites are glassy, often rounded or teardrop-shaped masses produced when surface rocks melt and are ejected into the atmosphere, then rapidly quenched during flight or on landing. Suevites are heterogeneous breccias containing glass fragments and shocked minerals embedded in a fine-grained matrix, typical of crater interiors. Impact melt rocks are coherent or brecciated bodies formed by the fusion of surrounding rocks during the impact, and they may host glass pockets and vesicles.

Diagnostic features of impactites include signs of shock metamorphism such as planar deformations features in quartz and feldspar, shatter cones, and, in some localities, high-pressure minerals such as coesite or stishovite. Textures may show melt pockets, glassy domains, and clast-melt brecciation.

Impactites are found at many known impact structures around the world, including large craters such as Chicxulub and Ries. They are important for constraining the timing and magnitude of impacts and for understanding post-impact processes and environmental effects. Dating is carried out on melt rocks, glass, and minerals using radiometric methods like U-Pb and Ar-Ar.

Impactites are distinguished from volcanic rocks by their shock features, formation mechanism, and association with craters, although glass chemistry can overlap across origins.