Iowa has an official state rock, the geode.
A geode is a round, hollow stone that, when carefully broken in half, reveals an interior of sparkling mineral crystals, usually quartz, that have grown inside.
Geodes are found in great numbers in Iowa, especially in the southeastern part of the state.
Geodes also are common in Brazil, Namibia, and Mexico.
Geode State Park is a state park located in Henry County, Iowa.