On July 14, 2000, agate was officially designated as Kentucky's state rock (Kentucky Acts ch. 146, sec. 1). The Kentucky Geological Survey was not consulted prior to this designation, which is unfortunate, because although beautiful agates are found in Kentucky, agate is scientifically a variety of the mineral quartz, and not a rock. Minerals are the building blocks of rocks. Rocks are composed of many minerals and are formed through sedimentary, igneous, or metamorphic processes, which, strictly speaking, agate is not. Now Kentucky has a state rock that is really a mineral, and a state mineral (coal) that is really a rock!
Agate, a microscopically crystaline form of quartz, a silicate mineral, has delicate and varying shades of color arranged in layers. In the typical occurrence the bands are irregular, curved, or in concentric patterns. Agate is used as an ornamental material or in semi-precious jewelry. The color banding is usually related to chemical impurities; for example, iron gives a red or orange color and manganese or calcium give black or blue colors.
Beautiful specimens of red, black, yellow, and gray banded agate have been discovered in Estill, Jackson, Powell, Madison, and Rockcastle Counties. These "Kentucky Agates" are derived from the Borden Formation of Early Mississippian age and can be collected along some river drainages where the Borden is exposed to weathering. Many of these agates are displayed at local rock shows.
The following are examples of Kentucky Agate, courtesy of Roland MacIntosh. For more information about these and other photographs of Kentucky Agate, contact Roland at firstname.lastname@example.org. All photographs here copyrighted 1999 by Roland MacIntosh.