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Prismatic rhabdites Similar to terrestrial (Earth) geology, primary structures help to model a meteorite's beginning formation over 4 billion years ago. Secondary structures can tell us of events forward of that time. These structures (secondary) almost always chronicle a story of violent activity with collisions and asteroidal core disruption, or the intense heating and cooling cycles of close passage solar orbits. Prismatic rhabdites (and plate rhabdites) are numerous in hexahedrite iron meteorites. They are inclusions of shreibersite exsolved from cooling taenite (face centered cubic austenite with more than 25%Ni in solid solution) occuring when the taenite could no longer accomodate moderate amounts of phosphorus. Microscopically, they resemble sparkling prisms of reflected light in taenite lamellae. Note the several orientations of neumann lines also in the lamellae. Meteorite: Coahuila, Iron IIAB, Mexico Scale bar - 200 um Image copyright 2023, New England Meteoritical Services |