Rocks and minerals of the Ozark Plateau
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Limestone. Common throughout Kansas, limestone is a sedimentary rock composed mostly of calcite (calcium carbonate, CaCO3). It is formed in marine environments by organic means—that is, from the remains of animals or plants—or by chemical deposition. Many animals and plants (such as oysters, corals, some sponges, sea urchins, plankton, and algae) take calcium carbonate out of the water and secrete it to form shells or skeletons. As these organisms die, they drop to the bottom of the ocean, lake, or river. Over time, the organic parts decay and the calcium carbonate accumulates to form limestone. Chemically deposited limestones are formed when calcium carbonate dissolved in water falls out of solution and settles to the bottom.
The limestones that crop out in the Ozark Plateau, which also contain chert, were deposited during the Mississippian subperiod. The best places to see these cherty limestones are roadcuts or steep cliffs along stream valleys. Economically, these Mississippian limestones were very important because they contained valuable lead and zinc ores.
Chert. Chert (or flint) is common in many Kansas limestones as nodules or continuous beds. It is opaque and ranges in color from white to gray or brown to black. It breaks with a shell-like (conchoidal) fracture, and the edges of the broken pieces are sharp. Chert is a sedimentary rock composed of microscopic crystals of quartz (silica, SiO2). Humans have used chert for thousands of years to make tools and weapons. In Cherokee County, chert, known in the Tri-State mining district of southwestern Missouri, southeastern Kansas, and northeastern Oklahoma as jasperoid, was commonly found among the waste at abandoned lead and zinc mines. (Note: these mines are closed to collecting.)
Galena. Galena is lead sulfide (PbS), the principal mineral of lead ore. It occurs as metallic to lead-gray, cube-shaped crystals that break into cubic, right-angled fragments. Some galena crystals are very large. Galena is heavy, has a metallic luster on fresh surfaces, has a gray-black streak, and is so soft that it will mark on paper. Galena was once mined in the Tri-State mining district, formerly one of the most important lead- and zinc-producing areas in the world.
Sphalerite. Sphalerite or zinc sulfide (ZnS) is the most important mineral of zinc ore. Also called zinc blende, blende, blackjack, and mock lead, pure sphalerite is nearly colorless, but it is commonly brown, yellow, black, or dark red because of impurities. It has a white to dark-brown streak, always lighter than the color of the specimen. The mineral crystals are usually shaped like triangular pyramids, with three sides and a base. Because it has good cleavage in six directions, sphalerite will break into 12-sided blocks. It has a brilliant resinous or metallic luster, and it can be scratched by a knife. Some sphalerite is found as massive deposits varying from coarse to fine grained. The best specimens found in Kansas are from the lead and zinc mines of Cherokee County.
Calcite. Calcite (calcium carbonate, CaCO3) is the primary constituent of limestone and is therefore one of the most common minerals in Kansas. Generally it is white or colorless, but it may be tinted gray, red, green, or blue. It can be scratched with a knife but not with a fingernail. Among the finest calcite crystals in Kansas are those from the lead and zinc mines of Cherokee County. Most of these are pale yellow and some are very large.
Buchanan, R., and McCauley, J. R., 2010, Roadside Kansas: A Traveler's Guide to its Geology and Landmarks: Lawrence, Kansas, University Press of Kansas, 392 p.
GeoFacts: Ozark Plateau (pdf)