Kentucky Agate

On July 14, 2000, agate was officially designated 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 agate is a microscopically crystalline variety of the mineral quartz, and not a rock. Rocks are composed of many minerals and are formed through sedimentary, igneous, or metamorphic processes. Kentucky has a state rock that is really a mineral, and a state mineral (coal) that is really a rock!

Agate has delicate and varying shades of color arranged in layers. 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. The bands are typically irregular, curved, or in concentric patterns. Agate is used as an ornamental material or in semiprecious jewelry.

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 rivers where the Borden is exposed to weathering. Many agates are displayed at local rock shows.

A new book contains hundreds of photographs and shows the many colors, shapes, and textures of agates. It is available from University of Kentucky Press ( or at many bookshops.

Microscopic photographs of Kentucky agates

Chemical analysis of agate banding demonstrates the higher iron content reflects red coloration.


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Last Modified on 2019-02-05
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