Kentucky Agate is Kentucky's official state rock. All agate is a mineral according to geologists. Most agate hunters say they are going rock hunting when in fact they are going mineral hunting. The mineral agate primarily is composed of silicone dioxide with inclusions of other minerals such as iron, magnesium, zinc, nickel, millerite, goethite, sphalerite and limonite.
Kenucky Agate was formed in the Borden layer of the MIssissippian geological age which according to geologists was between 225 and 375 million years ago. The shale of the borden formation is brown to green colored siltstone which is the matrix in which the agate was formed. The siltstone matrix exposed to the weather erodes and the agates slowly move down the hillsides into the streams in Powell,Estill and Jackson counties. We have more varied forms and colors of agate here in Kentucky than any other single known area in the world.
The forms include banded, fortification, moss, sagentic, plume, flame, cloud, veil, snowflake, eye and crazy lace. Some agates have two or more combinations of forms with variations from opaque to translucent. The colors range from single representations to complex combinations of brilliant red, orange, yellow, burgundy, oxblood, to the more subtle pastels of lavender, pink, pale green and grey. The red and black agate in Kentucky is very rare and ranks among the most expensive agates in the world. The yellow and black agate that is also extremely rare in the rest of the world is not quite as rare as the red here in Kentucky.
Kentucky agate quite often has fractures which were caused by tectonic palate movement and by exposure to the weather but the inherent beauty is still there. Some of the geode slices and halves that are not quite suitable for display specimens have the potential to makes some very fine gemstones.