The geode was designated the official state rock of Iowa in 1967 to promote tourism in the state. Iowa is known worldwide because of the large number of rare and beautiful geodes found in the state. The word "geode" is of Greek origin and means earth-like; geodes are shaped like the earth with a hard outer shell that when cut reveals a core of sparkling mineral crystals (usually quartz and calcite)
Southeastern Iowa is one of the state's best geode collecting areas. Geode State Park, in Henry County, is named for the occurrence of geodes. The geode is also the state rock of Oregon (thunder-egg).