Rock City is a park located on hillsides overlooking the

Solomon River The Solomon River, often referred to as the "Solomon Fork", is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed March 29, 2011 river in the central Great Plains of North America. The ...

Ottawa County, Kansas Ottawa County (standard abbreviation: OT) is a county located in the U.S. state of Kansas. As of the 2020 census, the county population was 5,735. The largest city and county seat is Minneapolis. History Early history For many millennia, ...

. It is 3.6 miles south of

Minneapolis, Kansas Minneapolis is a city in and the county seat of Ottawa County, Kansas, United States. As of the 2020 census, the population of the city was 1,946. History The community was originally called Markley's Mills, and under the latter name was laid ...

and just over 0.5 mile west of Kansas highway K-106 and the Minneapolis City County Airport on Ivy Road. In a patch of prairie about long and wide, Rock City contains three clusters of large spherical boulders. These three clusters contain a total of 200 spherical boulders. It has been designated as a

National Natural Landmark The National Natural Landmarks (NNL) Program recognizes and encourages the conservation of outstanding examples of the natural history of the United States. It is the only national natural areas program that identifies and recognizes the best ...

. The park, owned by a non-profit corporation, has a visitor center and picnic tables. A small admission fee, which is used to maintain this park, is charged. The remarkable size and spherical shape of these

rock formation A rock formation is an isolated, scenic, or spectacular surface rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock formation'' can also refer to specific sedime ...

was first noted by Bell.Bell, W.T., 1901, ''The remarkable concretions of Ottawa County, Kansas'', American Journal of Science, 4th Series, v. 11, p. 315-316. Later, these boulders were either noted or described by Gould,Gould, C.N., 1901, ''The Dakota Cretaceous of Kansas and Nebraska'', Kansas Academy of Science, v. 17, p. 122-178. Landes,Landes, K.K., 1935, ''Scenic Kansas'', Geological Survey of Kansas Bulletin, n. 36, 55 p. Shaffer,Shaffer, H.L., 1937, ''Concretions in the Dakota Sandstone'', Compass, v. 17, p. 87-90. Ward,Ward, H.K., 1938, ''Concretions of Rock City. Mineralogist'', v. 6, p. 23-24. and Swineford. Shaffer was the first person to map the distribution of these boulders at Rock City and investigate their

petrography Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The class ...

in detail.

Physical characteristics

The large spherical boulders in Rock City are giant calcite-cemented

concretions A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...

, typically called "cannonball concretions" because of their shape. They range in diameter from with the average diameter being . These concretions lie apart. Similar giant calcite-cemented concretions have also been found in a quartzite quarry within Lincoln County and in exposures of the similar age sandstones in Utah and Wyoming. These boulders consist of well-sorted, medium-grained

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

, which is tightly cemented by

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

. The sandstone consists of more than 95 percent

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...

. About 20 percent of the original sandstone, mostly

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...

grains, has been replaced by the calcite.

Pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...

, which is now oxidized to

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

, occurs within the calcite cement of these concretions as microscopic crystals and very small, knobby concretions. The pyrite concretions typically are about 30 cm (1-foot) in diameter. Also, included within these calcite concretions are smaller calcite concretions, which have been engulfed by the growth of the larger concretions. The host rock, which contained these spherical boulders, consists of well-sorted, medium-grained, highly porous, and friable sandstone. Being only weakly indurated by small amounts of iron oxide, sometimes seen as

Liesegang rings Liesegang rings () are a phenomenon seen in many, if not most, chemical systems undergoing a precipitation reaction under certain conditions of concentration and in the absence of convection. Rings are formed when weakly soluble salts are produc ...

(banding) at Rock City, it is considerably softer and very much more easily eroded than the calcite concretions. The sand comprising it accumulated within a river channel, which is part of the

Dakota Sandstone The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western Int ...

, which accumulated within a low-lying coastal plain. Differential cementation and later erosion of

cross-bedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...

inherited from the riverine sand, in which these concretions occur, created the "ornamentation", which these concretions exhibit.

Origin

In the past, the origin of the spherical boulders found at Rock City had been erroneously interpreted as glacial boulders, corals, concretionary masses of limestone, and normal erosional remnants of sandstone. Shaffer was the first person to recognize them as calcite-cemented concretions. From a detailed examination of the

mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proce ...

of these concretions and the carbon and oxygen isotopes of the calcite cement comprising them, McBride and others concluded that they formed as the result of diffusion of

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

through and precipitation of calcite within the sandstone containing them after being deeply buried. The

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

and

comprising these concretions came either from

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

, shells,

anhydrite Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...

, or some combination of these in addition to

bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemi ...

derived from oxidized

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...

from

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

outside of, but hydrologically connected to, the

. After the formation of the concretions, differential erosion of the considerably softer sandstone surrounding them exposed as free-standing boulders.

Gallery

Image:RockCityE21.jpg, Tree at Rock City Image:RockCityE23.jpg, A turtle-shaped rock Image:RockCityE24.jpg, A large, round rock Image:RockCityE25.jpg, Trees at Rock City Image:RockCityE22.jpg,

Hesperis matronalis ''Hesperis matronalis'' is an herbaceous plant species in the family Brassicaceae. It has numerous common names, including dame's rocket, damask-violet, dame's-violet, dames-wort, dame's gilliflower, night-scented gilliflower, queen's gilliflo ...

growing by a rock in May Image:RockCityE20.jpg, Looking towards Minneapolis, KS across rippling wheat fields in May

References

External links

Rock City Park, Kansas
Hours, prices, history *Kansas Geological Survey, nd
Rock City, Minneapolis, Kansas
*Biek, B., 2002
Concretions and Nodules in North Dakota
North Dakota Geological Survey, Bismarck, North Dakota. Explains how concretions are created. *Dietrich, R.V., 2002

The Wayback Machine. an
PDF file of ''Carbonate Concretions--A Bibliography''
CMU Online Digital Object Repository,

Central Michigan University Central Michigan University (CMU) is a public research university in Mount Pleasant, Michigan. Established in 1892 as the Central Michigan Normal School and Business Institute, the private normal school became a state institution and renamed Ce ...

, Mount Pleasant, Michigan. *Hansen, M.C., 1994
''Ohio Shale Concretions'' PDF version, 270 KB
Ohio Division of Geological Survey GeoFacts n. 4, pp. 1–2. *Heinrich, P.V., 2007
''The Giant Concretions of Rock City Kansas'' PDF version, 836 KB
BackBender's Gazette. vol. 38, no. 8, pp. 6–12. *Kansas Geological Survey, 2004
Educational Resources, Photos from Ottawa CountyOttawa County Map
KDOT
Rock Climbing at Rock City
{{authority control Geography of Kansas National Natural Landmarks in Kansas Protected areas of Ottawa County, Kansas

Physical characteristics

Origin

Gallery

See also

References

External links