A raised area at the center of the crater 0.8 km (0.5 mi) wide by 2.4 km (1.5 mi) long suggests that the impact caused a major upheaval of lower-lying rock—
breccia and
Mount Simon Sandstone, which lies beneath the surface and is much older than the rock layers in the area surrounding it. Additionally, Blue Rock, an exposed portion of
faulted Prairie du Chien
sandstone, lies at the south of the crater's edge, which can be viewed at Nugget Lake County Park.
Discovery of reidite While studying the effects of
erosion on areas of meteorite impact, researchers from the
University of Puerto Rico discovered a rare high-pressure mineral,
reidite, at the center of the Rock Elm impact site. Reidite is a dense form of
zircon (ZrSiO4) that is formed by the intense heat and pressure as is caused by an impacting meteorite. The reidite found at the Rock Elm structure is the oldest known example of the mineral. It has been found in other impact sites such as the Xiuyan crater in China; the
Chesapeake Bay impact crater in Virginia, United States; and the
Nordlinger Ries crater in Germany. == References ==