Mineral Commodities
Appalachian Plateaus, Interior Low Plateaus, and Central Lowland
The Appalachian Plateaus, Interior Low Plateaus, and Central Lowland provinces are characterized by flat-lying rocks of which those of Mississippian, Pennsylvanian, and Permian age crop out most extensively. At places along the border of the region older rocks are exposed. Each of the systems have limestone units that are quarried for use as crushed stone. Limestone of Pennsylvanian age, mainly the Vanport Limestone, is an important source of high-calcium limestone for chemical and metallurgical use and of cement limestone. Limestone units of Mississippian age, mainly the Ste. Genevieve, Monteagle, and Girkin (Gasper of former usage) Limestones, have important resources of high-calcium stone.
Ordovician Limestones and Dolomites
Several Ordovician carbonate rock units are exposed in the westernmost counties of the Appalachian Region in Tennessee (pl. 2) and were described by Hershey and Maher (1963, p. 66-75).
The oldest rocks exposed in the Appalachian Plateaus belong to the Knox Group and crop out in the Sequatchie Valley of Tennessee and Alabama. In Jackson County, Tenn., the Knox is overlain by the Wells Creek Dolomite which is about 130 feet thick and is similar in lithology to the dolomite of the Knox. The Ridley Limestone, younger than the Wells Creek, crops out in a limited area in Smith County, Tenn., and in counties west of Appalachia. It is about 93 feet thick and consists of light gray to gray thick-bedded dense fine-grained limestone and interbeds of sugary-textured magnesian limestone. Overlying the Ridley is the Lebanon Limestone which averages about 90 feet thick and consists of thin-bedded limestone similar in lithology to the Ridley. The Carters Limestone, the next youngest formation of the region, is exposed in Smith and DeKalb Counties, Tenn. It consists of an upper thin-bedded limestone similar in lithology to the Ridley. The Carters Limestone, the next youngest formation of the region is exposed in Smith and DeKalb Counties, Tenn. It consists of an upper thin-bedded unit about 50 feet thick separated by a thin metabentonite layer. The two units are similar lithologically, but the lower unit has interbeds of magnesian limestone. The only other Ordovician limestone unit exposed in the region is the Leipers Limestone which crops out in southwestern Franklyn County, Tenn. It averages about 75 feet thick and consists of bluish-gray fine- to medium-grained limestone and argillaceous limestone.
The Chickamauga Limestone crops out along Elk River, Limestone County, northernmost Alabama. According to Adams, Butts, Stephenson, and Cooke (1926, p. 122), the Chickamauga consists of a thin unit of rather thick-bedded limestone overlain by 50-75 feet of thin-bedded cobbly highly fossiliferous limestone with clay partings.
Other Middle Ordovician limestone units are exposed along the Kentucky River on the west border of Appalachia in central Kentucky. They include the Tyrone, Oregon, and Camp Nelson Limestones which are quarried for roadstone, concrete aggregate, and agricultural limestone.
Several hundred feet of Upper Ordovician thin limestone and interbedded calcareous shale are exposed in Adams, Brown, Highland, and Clermont Counties of southern Ohio and nearby counties in Kentucky (Stout, 1941, p. 46-108). Because of their high shale content, they have been quarried only locally for small amounts of crushed stone.
Silurian and Devonian Limestones and Dolomites
Silurian limestone and dolomite are found in Ohio and Kentucky (pl. 3, columns 10, 12) and Devonian limestone in the northern part of Otsego County, N.Y. Elsewhere in the Appalachian Plateaus, Interior Low Plateaus, and Central Lowland, Silurian and Devonian rocks consist mainly of shale. The well-known Columbus Limestone (Devonian) that is mined extensively in central Ohio extends into Appalachia in the subsurface and in some areas could be mined underground as it is in Summit County, Ohio, north of Appalachia.
The Silurian System of southern Ohio includes the Brassfield Limestone, West Union formation of Orton (1871), Cedarville Dolomite, Peebles Dolomite (1871) described by Stout (1941, p. 47-49, 51-110). The Brassfield consists of thin- to medium-bedded hard dense crystalline limestone and interbedded shale having a maximum thickness of about 70 feet. It makes a good construction stone and roadstone and is in part a high-calcium limestone. It is used as a cement limestone in southern Ohio, west of Appalachia. The West Union Dolomite or Formation is a medium- to thick-bedded coarsely crystalline, somewhat siliceous dolomite as much as 72 feet thick. The overlying Cedarville and Peebles Dolomites range from 40 to 120 feet in thickness and consist of massive porous to cavernous, crystalline relatively pure dolomite. They are mined for metallurgical use in Adams County. The Greenfield Dolomite is as much as 100 feet thick and consists of massive porous coarsely crystalline, relatively pure dolomite.
Limestone of Devonian age is mined in Otsego and Tompkins Counties, N.Y., mainly for concrete aggregate and roadstone, but some stone produced in Tompkins County is used as blast-furnace flux. The Onondaga Limestone is exploited in Otsego County and the Tully Limestone in Tompkins County. In central and western New York, north of the Appalachian counties, Devonian limestone is extensively quarried.
Mississippian limestone units crop out extensively along the western border of Appalachia in Alabama, Tennessee, and Kentucky and to a lesser extent along the boundary between the Appalachian Plateaus and the Valley and Ridge provinces. They crop out locally in western Pennsylvania and eastern Ohio. Limestone units in the eastern part of the Appalachian Plateaus and nearby Valley and Ridge include the following formations: Loyalhanna Limestone in southwestern Pennsylvania, Greenbrier Limestone, which extends from Pennsylvania through eastern West Virginia into southwesternmost Virginia, and Newman Limestone in eastern Tennessee (pl. 3, columns, 4, 7, 13, 15). Typical analyses of limestone in these formations are given in table 94.
Table 94. Chemical Analyses of Mississippian Limestones
In western Pennsylvania the Loyalhanna and Greenbrier Limestones and one or two other thin limestone units of Mississippian age have been mined on a small scale as sources of lime, roadstone, railroad ballast, and paving blocks (B. L. Miller, 1934, p. 130-131). The Loyalhanna Limestone, exposed only in southwestern Pennsylvania, is generally 40-60 feet thick, but at places is absent and at others is as much as 80 feet thick. The typical rock is a hard fine-grained calcareous sandstone in which quartz sand grains are cemented by CaCO3. It has been burned to make a natural mortar that does not need addition of sand. The Greenbrier Limestone in Fayette County is stratigraphically 40-50 feet about the Loyalhanna. It ranges from less than 10 to about 40 feet in thickness and consists of a dark thick-bedded relatively pure limestone that has been quarried to make furnace flux and high-quality white lime.
The Greenbrier Limestone attains its greatest thickness and is an important source of crushed stone in southeastern West Virginia and southwesternmost Virginia. In Lee and Scott Counties, Va., the Greenbrier consists of about 450 feet of dark- to olive-gray fine-grained to oolitic and granular limestone (Harris and Miller, 1958). In southeastern West Virginia, the formation consists of limestone and interbedded shale as much as 1,000 feet thick (McCue, Lucke, and Woodward, 1939, p. 28-29). The Greenbrier of this region contains some high-calcium limestone.
Hershey and Maher (1963, p. 51) gave the following information about the Newman Limestone of eastern Tennessee: The formation is about 1,200 feet thick in Blount County and consists of shaly limestone and limy shale. In Hawkins County, to the northeast, it thickens to 2,800 feet. The lower part of the formation is shaly and dolomitic, the middle part is more limy, and the upper part is shaly and has several beds of sandstone. In Bradley and Hamilton Counties to the southwest, it consists of shaly limestone in the lower part and contains beds of pure limestone in its upper part. Several limestone units consist of more than 95 percent CaCO3; these units and the Holston Limestone contain the purest limestone of eastern Tennessee.
The widespread Upper Mississippian rocks along the western border of Appalachia (pl. 2) include several limestone units that have been extensively mined for crushed stone. The limestone is characteristically low in magnesia, and although the amount of other impurities varies greatly, at least two formations, the Ste. Genevieve and Girkin Limestones contain abundant high-calcium limestone. The most widespread Mississippian limestone units cropping out in Kentucky, Tennessee, and Alabama, are from oldest to youngest: Warsaw Limestone, St. Louis Limestone, Ste. Genevieve Limestone, Girgkin (Gasper) Limestone (locally the Monteagle, Renault, and Paint Creek Limestones in Kentucky), and Glen Dean Limestone. In southern Appalachia, the sequence is underlain by the Fort Payne Formation which locally contains limestone beds. In Alabama it is overlain by the Bangor Limestone. In Ohio, the Maxville Limestone is the only limestone of Mississippian age. Chemical analyses of the limestone in some of these formations are given in table 94.
The following data about these Mississippian limestone formations have been summarized from several reports, including Adams and others (1926), Alabama; Hershey and Maher (1963), Tennessee; McFarlan (1943) and McGrain (1956, 1958), Kentucky; and Morse (1910) and Lamborn (1951), Ohio.
The Warsaw Formation is 80-100 feet thick in the southwestern Appalachian counties of Kentucky and in Tennessee; it thickens to a maximum of about 200 feet in northwest Alabama. It consists of variable amounts of interbedded limestone, shale, and sandstone. In Kentucky, the limestone is locally siliceous or argillaceous, whereas in Alabama it is somewhat purer and has been used for flux.
The St. Louis Limestone crops out extensively in northwestern Alabama and along the Pine Mountain fault in eastern Kentucky. In Kentucky the formation ranges from 30 to 117 feet thick, in Tennessee from about 180 to 200 feet hick, and in Alabama from 150 to 175 feet thick. The formation consists mainly of siliceous and cherty limestone in Kentucky. In Tennessee and Alabama the limestone is interbedded with dolomitic layers, but the rock is somewhat higher in total carbonate than in Kentucky, at places averaging as much as 95 percent. The St. Louis Limestone is quarried extensively for crushed stone, mainly roadstone and concrete aggregate.
The Ste. Genevieve and Girkin (Gasper) Limestones crop out in the same region as the St. Louis Limestone. The Ste. Genevieve is as much as 60 feet thick in northeastern Kentucky, about 80 feet thick in southern Kentucky, where it is the lower member of the Monteagle Limestone (Lewis and Thaden 1965), and 75-100 feet thick in northern Alabama. It is partly a high-calcium limestone. Hershey and Maher (1963, p. 80-83) described the Ste. Genevieve and Gasper of Tennessee as attaining a maximum exposed thickness of 300 feet and consisting of two rock types, a thick-bedded oolitic fragmental coarse-grained very pure limestone and a nonoolitic fine-grained to crystalline less pure limestone. Beds of oolitic limestone are as much as 30 feet thick and some average more than 97 percent CACO3. The Ste. Genevieve has been extensively mined for general-purpose crushed stone throughout its area of outcrop in Appalachia and as cement limestone in eastern Tennessee.
The Girkin or Gasper Limestone in northern Alabama is mainly thick-bedded oolitic limestone and interbedded fine-grained limestone about 100 feet thick. Like the Ste. Genevieve, it grades into a shale facies towards the west and south in Alabama.
The upper member of the Monteagle Limestone of Tennessee and southern Kentucky is equivalent to the Girkin (Gasper) and to the Renault and Paint Creek Limestones of western Kentucky (Lewis and Thaden, 1965). Locally it is more than 200 feet thick in Wayne County, Ky., but thins to the north and is 20 feet thick in Carter County. The upper member is similar in lithology to the Ste. Genevieve Member, in part consisting of massive oolitic high-calcium limestone.
The Glen Dean Limestone, the next youngest Mississippian limestone formation, crops out in Kentucky and Tennessee. It is 15-180 feet thick in Kentucky and averages 150 feet in thickness in Tennessee, although in Marion County, southern Tennessee, it attains a maximum thickness of 250 feet. In Kentucky the Glen Dean locally is the equivalent of the Bangor Limestone and consists chiefly of thick-bedded impure limestone and some interbedded pure limestone layers. At places it contains much interbedded shale. The Glen Dean of Tennessee is a medium- to thick-bedded fine- to medium-grained limestone and interbedded oolitic limestone and shale. The formation is mined for aggregate and roadstone.
The Bangor Limestone of Alabama is variable in thickness, ranging from about 100 feet to nearly 700 feet. It is thick-bedded, crystalline and oolitic, very pure, and is quarried as a source of high-calcium limestone, used mainly for flux.
The Maxville Limestone, the uppermost formation of the Mississippian System of Ohio, occurs in isolated outcrops in a belt extending from Muskingum County in the north to Scioto County in the south. Its spotty distribution results from erosion of the formation before deposition of overlying rocks of Pennsylvanian age (Lamborn, 1951, p. 20). Maximum thickness is about 200 feet. In Muskingum County, where it is extensively mined for use as crushed stone as well as for cement limestone and chemical and metallurgical limestone, it is about 35 feet thick (Lamborn, 1951, p. 241-242). Morse (1910, p. 100) stated that in Muskingum and Perry Counties the formation could be divided into two units, a lower massive clayey limestone and an upper of thin- to medium-bedded limestone with shale partings. The maximum thickness of the upper unit is 22 feet and that of the lower unit is slightly more than 25 feet in this area.
Pennsylvanian and Permian Limestones
Several thin limestone layers occur in the thick coal-bearing sequence of Pennsylvaniana and Permian age in Pennsylvania, Ohio, and West Virginia (fig. 68). Of these, the Vanport Limestone is extensively quarried as a source of flux stone and cement limestone as well as for aggregate stone and roadstone. The other limestone layers are generally either thinner or more impure than the Vanport and have been mined only locally as a source of roadstone, aggregate stone, and agricultural limestone. Selected chemical analyses of Pennsylvanian limestone are shown in table 95.
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Table 95. Chemical Analyses of Pennsylvanian Limestones
The following data pertaining to the limestone unit of the Pennsylvanian System have been taken from four reports: B. L. Miller (1934) and O'Neill (1964), Pennsylvania; Lamborn (1951), Ohio; and McCue, Lucke, and Woodward (1939), West Virginia. Limestone beds occur in each of the major rock series of the Pennsylvanian System, Pottsville group, Allegheny Group, Conemaugh Formation, and Monongahela Group. Their aggregate thickness, however, is small in comparison with the clastic rocks and coals.
Limestone units of the Mercer Formation of the Pottsville Group have been quarried in Ohio and western Pennsylvania. They are generally 2-4 feet thick but locally are as much as 10 feet thick and consist of hard dark-gray to black fossiliferous limestone. The upper Mercer Limestone is 15-40 feet stratigraphically above the lower Mercer limestone. The limestone has been quarried on a small scale as a source of agricultural limestone, flux stone, stone for lime, roadstone, and ornamental stone.
Limestone units of the Allegheny Group or Formation that have been mined are: Putnam Hill Limestone Member (Ohio), Vanport Limestone (Ohio, Pennsylvania), Johnstown Limestone (Pennsylvania), lower part Freeport formation (Ohio, Pennsylvania), and upper part Freeport Formation (Pennsylvania). The Putnam Hill Limestone Member ranges from a few inches to about 13 feet in thickness and averages about 3 feet. It is a gray to bluish-gray hard dense, locally cherty limestone, which is quarried at a few places in eastern Ohio as a source of agricultural limestone.
The Vanport Limestone crops out in western Pennsylvania and eastern Ohio. In Pennsylvania it has been mined extensively as a source of cement limestone, stone for lime, flux, agricultural limestone, and roadstone. It consists of dense massive- to thin-bedded gray fossiliferous somewhat argillaceous limestone generally less than 30 feet thick. It is low in MgCO3 and averages 90-95 percent CaCO3. The Vanport is of more limited extent in eastern Ohio, where it is generally 4-6 feet thick, having a maximum thickness of about 10 feet. It is gray to light brown, fine grained, and fossiliferous. The upper part is commonly cherty.
The Johnstown Limestone attains its greatest thickness, 8 1/2 feet, in Cambria County, Pa., where it has been mined in the past as a source of natural cement rock and stone for manufacture of lime. It is an argillaceous, ferruginous, and locally dolomitic limestone.
The lower and upper limestones of the Freeport Formation of eastern Ohio and western Pennsylvania are each 2-8 feet thick but locally attain a thickness of 15-20 feet. The two units are similar lithologically, consisting of light-gray to bluish-gray dense argillaceous and ferruginous limestone. They have been quarried locally as a source of agricultural limestone and roadstone. Formerly they were burned to make lime.
Limestones of the Conemaugh Formation that have been exploited for crushed stone, mainly roadstone, are as follows: Brush Creek Limestone Member (Ohio), Cambridge Limestone Member (Ohio), Ames Limestone Member (Ohio, Pennsylvania), Coleman Limestone of Platt and Platt (1877) and Wellersburg Limestone of Swartz (1922) (Pennsylvania), Clarksburg Limestone Member (Pennsylvania), Upper Pittsburgh Limestone Members (Ohio), Ewing Limestone Member (Ohio) and Lower Pittsburgh Limestone Member (Ohio).
The Brush Creek Limestone Member of southeastern Ohio consists of two layers of blue-gray hard cherty ferruginous limestone separated by a few feet of shale; the sequence is as much as 25-30 feet thick. The limestone has been quarried in Gallia and Lawrence County for roadstone.
The Cambridge Limestone Member, which crops out at many places in eastern Ohio, is recognized also in western Maryland, northern West Virginia, and western Pennsylvania. It varies greatly in chemical and physical character from place to place and only locally contains limestone suitable for roadstone. The member is thickest in Guernsey and Muskingum Counties, Ohio, where it is a siliceous limestone having a maximum thickness of about 12 feet. In Gallia County, Ohio, the Cambridge is 1-4 feet thick and consists of a relatively high purity limestone that has been quarried as a source of agricultural limestone and roadstone.
The Ames Limestone Member is the most widespread limestone formation of the Conemaugh Group in eastern Ohio, where it has been quarried at many places as a source of roadstone and to a lesser extent for agricultural limestone and fluxing stone. It generally is 1-4 feet thick but locally is as much as 15 feet thick and consists of gray, pink, or greenish hard crystalline fossiliferous limestone. In Pennsylvania, the Ames is thinner and less widespread. It has been mined on a small scale in only a few places as a source of lime.
B. L. Miller (1934, p. 640-652) describes several limestone members of the Conemaugh that had been exploited for crushed stone in Somerset County, Pa. These include the Coleman Limestone Members of Platt and Platt (1877), Ames (Berlin) Limestone, Elk Lick (Wellersburg or Barton or others), Limestone, Clarksburg Limestone, and Upper Pittsburgh Limestone Members. The limestones are in layers ranging from 3 to 10 feet in thickness in a sequence of clastic rocks and coals having an aggregate thickness of 200-300 feet. The Berlin and Wellersburg contain relatively pure limestone; the others are somewhat argillaceous. The Upper Pittsburgh Limestone Member also has been exploited on a small scale at a few localities in Ohio as a source of agricultural limestone and roadstone.
Limestone units of the Monongahela Group or Formation that have been exploited are as follows: Redstone Member (Ohio, Pennsylvania, West Virginia), Fishpot Member (Ohio, Pennsylvania), Benwood Limestone Member (Ohio, West Virginia, and Pennsylvania), Uniontown Limestone Member (Ohio, Pennsylvania), and Wanesburg Limestone Member (Pennsylvania).
The Redstone Member has been quarried for agricultural limestone and roadstone in Ohio, for fluxing stone and burned agricultural lime in Pennsylvania, mainly in Fayette County, and for crushed stone in West Virginia. In Ohio, the Redstone varies considerably in thickness, being as much as 40 feet thick and consisting of several layers of gray to dark-bluish-gray dense limestone separated by thin layers of clay or calcareous shale. In Fayette County, Pa., the member consists of as much as 10-20 feet of gray relatively pure limestone. In northern West Virginia, the Redstone generally is 6-9 feet thick and consists of light- to dark-gray fine-grained nodular to massive ferruginous limestone.
The Fishpot Member has been quarried for agricultural limestone and roadstone in Ohio, for fluxing stone and burned agricultural lime in Pennsylvania, mainly in Fayette and Westmoreland Counties, as a source of fluxing stone and burned lime. Where best developed in Ohio, the Fishpot is as much as 35 feet thick and consists of a thin- to medium-bedded light-brown to dark-gray hard dense limestone and interbedded shale. Some rock is dolomitic. The Fishpot of Fayette County, Pa., also is as much as 35 feet thick and ranges from very impure ferruginous limestone to relatively pure limestone that is well suited for lime and fluxing stone.
The Benwood Limestone Member is one of the most persistent and thickest limestone units of Pennsylvanian age in Ohio, Pennsylvania, and West Virginia. It has been exploited as a source of lime, roadstone, and agricultural limestone. The member is 52-65 feet thick in Ohio and consists of dark hard thin- to thick-bedded limestone with partings of calcareous shale. It reaches a maximum thickness of 160 feet in Allegheny County, Pa., where it consists of several beds of limestone separated by thick layers of shale.
The Uniontown Limestone Member has been quarried in Ohio and Pennsylvania, as a source of flux stone, lime, agricultural limestone, and roadstone. It is generally 10-30 feet thick and is similar to the Benwood in consisting of thin- to thick-bedded limestone and abundant interbedded shale. The limestone is locally dolomitic and argillaceous.
The Waynesburg Limestone Member has been mined on a small scale at several places in western Pennsylvania where it is as much as 35 feet thick. It consists of interbedded limestone and shale similar to the Uniontown.
Limestone of the Dunkard Group of latest Pennsylvanian and Permian age that have been exploited include the Lower, Middle, and Upper Washington Limestone Members, the Blacksville Limestone Member of White (1891), and the Jollytown Limestone Member, all of the Washington Formation. They crop out in western Pennsylvania where they have been exploited for aggregate stone, roadstone, and agricultural limestone. They occur as layers a few feet to about 30 feet thick interstratified with sandstone and shale in a sequence ranging from 150 to 220 feet thick. They layers consist of light-gray to black hard argillaceous to relatively pure limestone.
Limestone units of the Greene Formation of Permian age which overlies the Washington Formation within the Dunkard Group, have been exploited for roadstone and lime in western Pennsylvania, mainly in Washington and Greene Counties. They range from 6 to 12 feet in maximum thickness and consists of gray to black argillaceous to relatively pure limestone.
Resources of limestone and dolomite in Appalachia are widely distributed and so abundant as to be virtually inexhaustable (sic). Most are suitable for crushed or broken stone for construction, road building, and related uses, and can also be used for agricultural limestone. Because of their wide distribution, these products are within comparatively short haulage distances of major markets and constitute a vital resource in the expanding economy of Appalachia. Cement limestone, of more restricted distribution, is very abundant in some regions and is the basis for the large cement industry in Appalachia.
High-calcium limestone and high-purity dolomite suitable for chemical and metallurgical uses are the most valuable types of carbonate rocks. They occur in minable quantitites only locally and in only a few of the formations in Appalachia. According to Gillson and others (1960, p. 150-159) high-calcium limestone for chemical and metallurgical use is produced mainly from the following formations and members: (1) Valentine Member (of Field, 1919) of the Curtin Formation (of Kay, 1943) in central Pennsylvania; (2) Vanport Limestone in western Pennsylvania; (3) Mosheim Member of the Lenoir Limestone in the Eastern Panhandle of West Virginia; (4) New Market Limestone (equivalent to the Mosheim) in western Virginia; (5) Greenbrier Limestone in southwestern Virginia; (6) Holston Limestone in eastern Tennessee; (7) Conasauga, Longview, Newala, Bangor Limestones in northern Alabama; (8) upper member of the Monteagle Limestone and its equivalents (Paint Creek and Girkin "Gaspar" Limestones) in eastern Kentucky. High-purity dolomite for metallurgical use is produced only from the Tomstown Dolomite in the Eastern Panhandle of West Virginia, the Ketona Dolomite in northern Alabama and the Peebles Dolomite of Foerste (1929) in Adams County, Ohio.
The formations are potential sources of high-calcium limestone in areas other than where they are being mined. Probably Mississippian limestone, the Greenbrier of southwestern Virginia and eastern West Virginia, the Ste. Genevieve and upper members of the Monteagle Limestone, and the Girkin (Gasper) Limestones along the west side of the Appalachia warrant development for chemical use. The best potential sources of high-purity dolomite, other than the Tomstown, Ketona, and Peebles Dolomites now mined, are the Shady Dolomite found along the eastern side of the Valley and Ridge province from northern Alabama to southwestern Virginia, dolomite in the Knox Group in eastern Tennessee, and the Cedarville Dolomite in southern Ohio.
By Alice E. French, U.S. Geological Survey, and
Nils A. Eilersten, U.S. Bureau of Mines
Abrasives are substances that are used to grind, polish, abrade, scour, clean, or otherwise remove solid material by rubbing and impact (Ladoo, 1960, p. 1). They may natural or manufactured: Natural abrasives include all minerals and rocks which are used for abrasive purposes without chemical or physical change other than crushing, shaping, or bonding into suitable forms. Manufactured or artificial abrasives are made either by heat or chemical change from metals or mineral raw materials.
Natural abrasives should possess certain properties, among which are hardness and toughness, proper grain or particle size and shape, suitable fracture or cleavage, and a high degree of uniformity and purity. For some uses it is desirable that they may be chemically inert and stable at high temperatures.
Abrasives are classified into three groups according to hardness (Ladoo, 1960, p. 2), those of superior hardness (7-10 on the Mohs' scale), intermediate hardness (5.5-7), and inferior hardness (less than 5.5). Among the materials of superior hardness are diamonds with a hardness of 10 followed in decreasing order by corundum, emery, and garnet. In the intermediate hardness range are such minerals and rocks as flint, quartz, quartzite, sandstone, silica sand, feldspar, perlite, and pumice. Natural materials of inferior hardness include chalk, clay, diatomite, iron oxides, limestone, rottenstone, talc, and tripoli.
Abrasives, both natural and artificial are used in various forms, such as powders, loose grains, bonded grains in various shapes, coated grains, and as massive material. Each has a special use depending on the type of abrasive material. Loose grains and powders are used for surfacing and polishing stone and glass, sawing stone, sand blasting, grinding lenses, polishing gem stones, manufacture of grinding and buffing wheels, and in scouring compounds, soaps, and toothpowders. Bonded abrasives consist of grains bonded or molded and pressed into articles such as grinding wheels, bricks, blocks and stones for sharpening and polishing. Coated abrasives are materials such as sand paper and emery cloth. Massive materials are cut and shaped and used as grindstones, millstones, and tube-mill liners (Stuckey, 1965, p. 346).
Artificial abrasives have replaced natural abrasives to a large extent for grinding metal because their properties can be varied and accurately controlled to suit different needs. Modern high-speed industrial machining requires a high degree of accuracy and uniformity in specialized tools that cannot be achieved with natural abrasives. Artificial abrasives include electric-furnace products, chemical precipitates, and miscellaneous manufactured products. Abrasive grains are produced from a wide variety of materials and may be used as precisely sized loose grains or combined with other materials for making bonded shapes, coated abrasives, abrasive tools, cleaners, polishes, and grinding paste. Artificial abrasives include materials such as the oxides of cerium, chromium, aluminum, iron, tin, and zirconium; silicon, titanium, boron and tungsten carbides; zirconium silicate and hard burned clay; and metallic abrasives such as steel balls and shot, angular steel grit, and steel, brass, and copper wool.
Natural abrasives are interchangeable with artificial abrasives and are preferable for many general purposes because they are less costly. Some natural abrasives have become specialized for certain uses, like almandite garnet for which no satisfactory substitute has been found. Mined in New York State, it is processed and used extensively for coating abrasive papers and cloth and for grinding glass and lenses. Hard natural abrasive materials such as silica sand, corundum, garnet, flint, and chert, used for sand blasting, compete with artificial abrasives such as fused alumina, silicon carbide, and steel shot. Use of any particular abrasive for this purpose largely depends on cost factors and the hardness of the object being scoured by sand blasting.
Both natural and artificial abrasive grains are bonded by various substances such as resins, rubber, shellac, or vitrified ceramic mixes to produce grinding wheels and blocks, bricks and sticks which are further shaped by cutting for marketing as oilstones, synthetic stones, and razor and cylinder hones. Such artificial stone has replaced to a large extent the natural stone which is quarried and sawed to various shapes.
Most abrasive materials are prepared for a specific industrial use and sold at prices that vary widely depending on specifications. Domestic garnet marketed to specification has a variable value depending upon particle size. New York abrasive garnet grains range in price from 12 3/4 cents per pound for coarser sizes in carload lots to 53 cents per pound for micron-sized powder in retail lots (Ambrose, in U.S. Bur. Mines, 1965a, p. 355-359). According to Metal and Mineral Markets (1965), the market value of ground and sized amorphous silica ranges from $27 a 50-pound bag, 90-98 percent silica ground to -10 microns. Rose and cream-colored tripoli, ground to -40 mesh (single grinding), or double ground to -110 mesh is valued at 2 3/4 cents per pound, and air floated to -200 mesh, 3 cents per pound.
In 1964, the total reported value of natural and artificial abrasives sold or used in the United States was $155.2 million, of which $65.7 million was produced domestically and $89.5 million was imported. Domestically produced natural abrasives include tripoli, garnet, emery, and special products such as grinding pebbles, tube mill liners, and natural silica abrasive for oilstones and other sharpening stones. Not included are silica sand, quartz, ground and calcined clays, lime, talc, ground feldspar, river silt, slate flour, and others for which detailed production data are not available. In the 20-year period 1944-64, the value of artificial abrasives sold or used in the United States has more than doubled from $24.8 million in 1944 to $63.4 million in 1964.
Although there has been a general decline in use of natural abrasives (table 100), natural silicate abrasive grains and powder produced from garnet, silica sand and quartz, pumice, tripoli, and rottenstone continue to find preference for certain special uses as do the soft nonsiliceous abrasives such as feldspar, chalk, and china clay. It is primarily in the field of hard abrasives that artificial abrasives dominate.
Continued industrial expansion in the United States will no doubt create additional demand for various types of abrasive materials. A careful study of natural abrasive resources and extensive research in their physical properties and potential uses may be needed to rejuvenate the industry. Stone abrasive products formerly produced in Appalachia, such as solid natural-stone wheels, hones, whetstones, oilstones, and polishing stones, are still in demand, but are imported.
Many types of natural abrasive materials are found in Appalachia and have been used at some time. Among these are corundum, emery, garnet, various forms of silica and sand, feldspar, rottenstone, and tripoli. At present, output is confined to grindstones from Washington County, Ohio, rottenstone from Lycoming County, Pa., and silica from alaskite in Mitchell County, N.C., and Campbell and Franklin Counties, Tenn. From 1922 through 1945, Appalachia produced a variety of special abrasive sandstone products, including grindstones and pulpstones from Ohio and West Virginia and oilstones, whetstones, and scythestones from Ohio. By 1946, only grindstones continued to find favor in competition with bonded or coated abrasives. Grindstones and pulpstones were produced from sandstone quarried mainly in Coshocton, Holmes, Jefferson, Morgan, and Washington Counties, Ohio, and in Jefferson and Monongalia Counties, W. Va. Quarries in Scioto County, Ohio, furnished natural abrasive stone products, oilstones, whetstones, and scythestones as late as 1940. Tripoli was mined in Bradley County, Tenn., from 1924 through 1933. Garnet was recovered as a byproduct of kyanite milling in Yancey County, N.C. during the period 1936-43.
Artificial abrasives, aluminum oxides and carbides of considerable value were manufactured in Calhoun County, Ala., from 1925-1952.
Table 100 shows the annual values of abrasives produced in Appalachia during the period 1922-64.
Table 100. Total value of abrasive materials produced in
the
Appalachian Region for 1922-64. (Source: U.S. Bur. of
Mines)
(Please note that the individual abrasive materials will not be presented here. If you are interested in which subjects are covered, check the Table of Contents.)
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