From Ger. Quarz "rock crystal," from M.H.G. twarc.
kuârtz-e tošidé, ~ šokidé
Fr.: quartz choqué
A form of quartz that has a deformed microscopic structure caused by intense pressure which alters the crystalline structure of quartz along planes inside the crystal. It was first discovered after underground nuclear bomb testing. It is found worldwide at the boundary between Cretaceous and Tertiary rocks. This is further evidence (in addition to iridium enrichment) that the transition between the two geological eras was caused by a large meteorite impact.