In Kentucky, many economic minerals occur in tabular or lenticular bodies known as veins. The mineralization is commonly localized in faults, fractures, and joints. A fault is a fracture or break in the continuity of a body of rock along which observable displacement or movement has occurred parallel to the plane of fracture. In many instances, faults of large displacement are accompanied by many small faults spread over a wide area. This type of complex faulting is referred to as a fault zone. Because of the resistance to movement of one large rock mass against another, much of the material along a fault is crushed or ground into a fine-grained, clay-like mass called fault gouge, or broken into larger angular fragments called fault breccia.
In the Central Kentucky Mineral District and the Western Kentucky Fluorspar District, minerals occur in veins associated with the fault zones.These minerals are barite, sphalerite, fluorite, galena, celestite, dolomite, and calcite. Occasionally, some secondary minerals such as smithsonite, cerussite, and anglesite may be observed. Some witherite has also been observed in central Kentucky veins.