The prairie agate was declared the state rock by legislative action in 1967. Agate is a semiprecious stone, and Nebraska has an abundance of it, especially in the Oglala National Grassland. Agate is a variegated quartz noted for its layered varieties. In most specimens, the bands are coarse and differ in color and translucency, as well as in compactness and porosity. The prairie agate, distinguished from most other agates because it seldom has these bands, is still colorful, has a rounded irregular shape and is popular for jewelry.