Iron deposits near Owingsville in Bath, Powell, and Estill Counties were mined as late as the 1900's. These iron ores occur in an oolitic limestone in the Brassfield Formation of Silurian age. Specimens of limonite and hematite may also be found in this area. Iron ore was also mined in northeastern Kentucky in Greenup, Boyd, and Carter Counties, where iron ore occurs in the Upper Mississippian and Lower Pennsylvanian rocks. Siderite and limonite nodules also occur at this locality. Some iron ore occurs in the Tertiary gravels of western Kentucky, and they were mined at one time. Numerous ferruginous nodules, concretions, and irregular bodies occur in the sandstones of eastern Kentucky. These are mainly massive ironstone bodies with few or no crystals visible.
Most mining of these iron deposits was halted in the early 1900's with the discovery of the massive iron deposits in the Lake Superior region.Phosphate
Phosphate deposits consisting dominantly of microcrystalline apatite were mined from the Lexington Limestone in central Kentucky in Woodford, Fayette, Franklin, and Jessamine Counties in the early 1900's. These phosphates are thin bedded and weather easily in streams to form soft, dark-colored phosphate sands. Any cave or outcrop in the phosphatic portion of the Tanglewood Member would yield specimens of collaphane. It is possible that some nodules or geodes might contain crystals of some phosphate minerals. Phosphate is commonly used as a fertilizer; thus, the exceptional fertility of some Blue Grass soils.
Geodes are defined as spherical or oblong bodies filled or partially filled with layered mineral matter, some with crystals projecting inward. Their sizes range from less than an inch to several feet in diameter. Most geodes have an outer shell of chalcedony, and an interior lined with quartz crystals projecting inward. Less commonly, calcite or dolomite crystals are found on the inside, either alone or associated with bitumen, barite, galena, fluorite, quartz, limonite, sphalerite, pyrite, selenite, or celestite. Geodes differ from concretions in that they are hollow and the crystals grow inward from an outer shell; concretions are solid, grow from the center outward, and are generally noncrystalline, although some crystals have been observed. The Fort Payne and Warsaw-Salem Formations of Mississippian age, which crop out in a general semicircle around the Outer Blue Grass and southward into Tennessee, are noted for their abundant geodes. In many places, creeks that drain these formations are filled with geodes, and several mineral varieties can be collected, particularly during low-water stages. Other locations for geode collecting include the tributaries of the Green River in south-central Kentucky and along ancient terraces of the Kentucky River. The Green River has produced some very large geodes (2 feet in diameter) and countless smaller ones. The terraces along the Kentucky River are usually situated near the present course of the river and their locations can be found on geologic quadrangle maps.Concretions and Nodules
Concretions are formed by the deposition of distinct minerals, different from the surrounding rock, very firmly cemented around a nucleus. They are generally lens shaped, although some have irregular, complex forms. The most common cementing materials are calcite, siderite, and silica. Parts of plants and animals may serve as nuclei, and well-preserved fossils may be found in concretions. In Kentucky, large concretions of siderite and calcite, which used to be called ironstones, are found in shales associated with coal beds. Nodules are another type of irregularly shaped minerals that occur in sedimentary rocks. The most common minerals that occur in nodules are siderite, gypsum, calcite, quartz, and barite/celestite. Siderite nodules, concretions, and liesegang (iron-stained) banding are a very common type of mineralization found in eastern and western Kentucky sandstones.Meteorites
A meteorite is a fragment of stony or metallic interplanetary rock thought to have formed in the asteroid belts billions of years ago when the earth and solar system were first formed. The most common are the stony meteorites, which are composed of silicate minerals (mainly olivene) and the iron meteorites (siderites) composed of iron, nickel, and accessory minerals. Meteorites have been recovered in 27 locations in Kentucky, including Bath, Bullitt, Livingston, Franklin, Allen, Carroll, Grant, and McCreary Counties. Another unconfirmed report of a meteorite has come from Lewis County. Once a large meteorite strikes a planet, the energy and shock waves eject rock material and brecciate other strata, forming the circular structures associated with meteorite impact structures. The deformation caused by the meteor impact is a very rapid geological process. These impact structures are also called astroblemes. Kentucky has three and possibly four meteorite impact structures. Jeptha Knob in Shelby County, the Versailles structure in Woodford County, and the Middlesboro structure in Bell County are all circular, faulted structures that have some shatter breccia. The Muldraugh Dome or Knob structure in Hardin County may also be an impact structure. Because the earth has weathered and erosion is ongoing, traces of impact structures are uncommon. Approximately 200 impact structures are known on the earth.
Some minerals or unusual rocks may be found near these impact structures, namely part of the meteorite itself, brecciated rocks struck by the meteorite, and possibly some iron, nickel, or sphalerite minerals formed during or after the impact.