Formula: ZrSiO4 Tetragonal
Description: Reidite, a polymorph of zircon, is an extremely rare mineral that forms under very high pressures, such as are associated with large extraterrestrial impact structures (meteor craters).
PIERCE COUNTY: Reidite has been documented by electron backscatter diffraction as occurring in a polymict breccia within the Mt. Simon sandstone from the Rock Elm impact structure. It has been found both as sets of lamella within tiny zircon grains as well as “randomly oriented sub-micrometer granules along margins and within intrageanular voids” in the breccia. The presence of this high-pressure mineral, known from only a handful of impact sites worldwide, supports the proposed impact origin of the Rock Elm anomaly (Cavosie and others, 2014, 2015).