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AGS / Minerals / Industrial / Descriptions O - Z


Phosphate Rock

Phosphate rock can be any rock or sediment with sufficiently high concentrations of some form of the mineral fluorapatite (Ca5(PO4)3F) to be of commercial value. Fluorapatite composes the mineral part of vertebrate bones and teeth. Collophane is the massive fine-grained variety of apatite in phosphate rock. Commercial phosphate rock is usually sedimentary in origin and is used primarily as a plant nutrient, either by direct application to the soils as a powdered product or in the manufacture of superphosphate or triple super-phosphate fertilizer. Elemental phosphorus and phosphoric chemicals are also derived from phosphate rock and are used in detergents, insecticides, matches, fireworks, and many other products.

Phosphate rock was discovered in Arkansas in 1895. During the early 1900’s, several thousand tons were mined by underground and surface methods in Independence County and shipped to a plant in North Little Rock for processing into super-phosphate fertilizer. This operation ceased when higher grade material from Tennessee and Florida entered the market. Potential commercial deposits are present in the Cason Shale (Ordovician-Silurian) along the White River Valley and nearby areas in Independence, Stone, Izard, Searcy, and Marion Counties. A deposit in Upper Mississippian rocks along the Searcy-Van Buren County line a few miles south of Leslie was mined during the 1960’s. Other minor phosphate rock deposits are known, but have not been explored.

Since phosphate rock is a low-cost commodity, certain cost-limiting conditions must be met for a deposit to be minable. A typical phosphate mining operation uses open-pit methods, is a large volume producer, and requires large amounts of water for upgrading the raw material. Low-cost transportation to markets is also essential. Current economic conditions preclude commercial utilization of the Arkansas phosphate rock, but could become significant when supplies from other states are exhausted.

Branner, J. C., 1897, The phosphate deposits of Arkansas: American Institute of Mining Engineers Transactions, v. 26, p. 580-598.
Wells, C. J., 1949, Hickory Valley phosphate deposit in Independence County, Arkansas: Arkansas Resources and Development Commission, Division of Geology Bulletin 19, 37 p.

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Quartz (Industrial)

Quartz, or silica (SiO2), is a hard, brittle, usually colorless or white, nonmetallic mineral that exhibits considerable resistance to weathering. Quartz is composed of the two most abundant elements (silicon and oxygen) in the earth's crust, making it common on the earth's surface. Hydrothermal quartz crystals and milky "bull" quartz veins are a common and striking geologic feature of the Ouachita Mountain region of Arkansas. Quartz as single crystals and groups or clusters of clear rock crystal from Arkansas are widely known for their aesthetic beauty. The mineralogical profession has recognized Arkansas quartz crystal as some of the best and purest in the world. Because of this, and the popularity of quartz with many tourists who visit Arkansas each year, the Arkansas General Assembly of 1967 established Act 128, which designated quartz crystal as the official State Mineral.

Recently, large quantities of quartz crystals have been mined from open pits in two districts in Garland and Montgomery Counties and, to a lesser degree, in Saline and Pulaski Counties. Specimens are sold mostly to tourists, museums, schools, and private collectors domestically and abroad. Collecting in mines is a popular recreational activity, although a fee is required. The U.S. Forest Service has a free quartz crystal collecting site named Crystal Vista in the Ouachita National Forest south of Mount Ida in Montgomery County.

Most of the crystal deposits mined in the Ouachita Mountains formed as veins which filled cavities or fractures in the Crystal Mountain and Blakely Sandstones (both Ordovician). Individual quartz crystals up to 5 feet long and weighing over 500 pounds and clusters up to 15 feet long by 10 feet wide, weighing over 10 tons, have come from Arkansas' mines. Exquisitely developed large single crystals and quartz clusters may be wortj thousands of dollars.

Radiometric dating of adularia, a hydrothermal potassium feldspar present in some quartz veins, yields Late Pennsylvanian to Early Permian ages for the mineralization, placing the major period of quartz vein formation at the end of the Ouachita Mountain orogenic (mountain building) cycle. In the Ozark region of north Arkansas, minor deposits of clear to white, stubby quartz crystals are present, associated with lead and zinc deposits and lining small cavities, nodules ,or concretions in some Ordovician and Mississippian sedimentary units.

Clear, colorless, untwinned quartz crystals had important uses as oscillators in radio equipment and in periscopes, gun sights, and other optical equipment, particularly during World War II. More recently, quartz has been mined for use in electronics, fiber optics, and as the source of silica in the production of synthetic quartz crystals. One company produces the chemical feedstock (lasca) for synthetic quartz growth. Annual production varies from 450 to 570 tons. The milky quartz is mined from veins in an open pit near Paron, Saline County, and trucked to the processing plant near Jessieville, Garland County. There it is crushed, washed, cleaned in an acid bath, then hand sorted to 4 different grades. The quality of lascas produced from Arkansas is equal to or slightly superior to lascas produced in Brazil, and are usually less variable. Some crushed milky quartz was mined in Saline County and used as decorative surface aggregate in precast concrete.

Milky "bull" quartz veins in the Ouachita Mountain region are up to 60 feet thick and hundreds of feet in length. They may strike in any direction, but generally trend across the structure of the host rock. These veins occur in highly deformed shale sequences in the Ouachita Mountains region. Milky quartz veins have been investigated by several companies and individuals for their industrial quartz potential. With the increasing demand by tourists, collectors, museums, and the new commercial applications of synthetic quartz, prices of clear quartz crystal and processed milky quartz should rise.

Engel, A. E. J., 1952, Quartz crystal deposits of western Arkansas: U. S. Geological Survey Bulletin 973-E, p.173-260.
Howard, J. M., and Stone, C. G., 1988, Quartz crystal deposits of the Ouachita Mountains, Arkansas and Oklahoma, in Colton, G. W., ed., Proceedings of the 22nd Forum on the Geology of Industrial Minerals: Arkansas Geological Commission Miscellaneous Publication 21, p. 63-71.

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Quicklime

Limestone was quarried by Arkansas Lime Company in Independence County from an open pit mine at Limedale for the production of quicklime. The company started in 1906, incorporated in 1910, and later became a subsidiary of United States Lime and Materials of Dallas, Texas. The deposit was unique for the Boone Formation (Mississippian) in that it was devoid of chert. Drilling and blasting released the stone from the outcrop and provided first-order breakage. The rubble was then railed to a nearby crushing facility where the stone was further crushed, screen-sorted into size classes, and stored. Limestone needed for high-purity applications (quicklime and food supplements) was usually hand-sorted at the mine. In the manufacture of quicklime, the limestone was crushed to lump size (usually 5-8 inches) and heated in a kiln to temperatures of around 2,000° F. The calcination process drives off carbon dioxide from the calcite, forming calcium oxide (quicklime). Additionally, limestone, also used as a source of nutritional calcium, was ground into a powder, mixed with other supplements and binders, and reformed into pills or capsules.

The deposit was mined out and the operation closed after nearly 90 years of continuous production in the mid-1990s after an extensive local exploration program failed to find another chert-free deposit.

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Salt and Chlorine

Salt (the mineral halite – NaCl) is one of society's basic needs. Its use goes back to earliest recorded history (3,500 B. C.). Pure halite consists entirely of sodium and chlorine in an atomic ratio of 1:1. Rock salt is the solid form. When dissolved in water it becomes saltwater – or brine if the salt content is high.  Salt has many uses in modern society and is an important raw material of industry. It is the starting material for the manufacture of both the bulk of elemental sodium and chlorine used in industry, and most compounds of either element. Among other things, sodium is used to make caustic soda, large quantities of which are used in the pulpwood and metallurgical industries.

Chlorine is used to manufacture polyvinylchloride (PVC, an important plastic) and muriatic (hydrochloric) acid, as a water purifier, and as a bleaching agent. Huge tonnages of rock salt are used to de-ice highways, streets, and sidewalks. Much salt is used as a flavor-enhancer and a preservative in the food-processing industry. A volumetrically minor, but very important product, is the table salt used in most homes as a seasoning agent.

The most important commercial source of salt is rock salt. It occurs in evaporite layers deposited by the evaporation of water from oceans or saline lakes. Commonly, rock salt is interbedded with shale, gypsum, and anhydrite. Because rock salt may flow under pressure, it also occurs in domes that were forced or extruded into younger overlying sedimentary rocks. Salt is often mined underground or recovered by the evaporation of water obtained from the seas, saline lakes, and brine springs or wells. In Arkansas' past, Native Americans and early settlers obtained salt from evaporation of small bodies of saline water and brine springs in several counties, mostly in the central part of the state.

Although there are major deposits of both rock salt and brine in the subsurface of south Arkansas, there has been no commercial recovery of salt or chlorine from the subsurface. The salt-bearing Louann Formation (Jurassic) in southern Arkansas extends in the subsurface from Miller and Hempstead Counties in the west to Chicot County in the east. The Louann in south Arkansas represents the northernmost edge of salt-bearing units in the Gulf Coast Basin, the largest of 4 major basins containing salt in the United States. Some deep wells have encountered more than 1,000 feet of salt in the Louann. Eventually, it may be economical to utilize these bedded deposits by deep-well injection of water into the salt-bearing units and extracting the resultant brines for processing. Consequently, the remaining cavity might have value for storage.

Oil-field brines, most notably those in the Smackover Formation (Jurassic), are present throughout southern Arkansas. A collection of 284 Smackover brine samples was analyzed for chlorine and determined to average more than 171,000 parts per million, or nine times the chlorine content of typical seawater. Presently, the oil-field brines in southern Arkansas have unknown potential for halite and other salts.


Bell, H. W., 1933, Discovery of rock salt in deep well in Union County: Arkansas Geological Survey Information Circular 5, 24 p.
Collins, A. G., 1974, Geochemistry of liquids, gases, and rocks from the Smackover Formation: U. S. Bureau of Mines Report of Investigations 7897, 84 p.
Imlay, R. W., 1949, Lower Cretaceous and Jurassic Formations of southern Arkansas and their oil and gas possibilities: Arkansas Resource and Development Commission, Division of Geology Information Circular 12, 64 p.

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Sand & Gravel

Deposits of sand and gravel are widely distributed across all of Arkansas. Major deposits are present as sedimentary units, on talus slopes, and as alluvial deposits in the flood plains, beds, and terraces of rivers and streams. Most of these unconsolidated deposits may be mined from open pits. Certain areas of the state are particularly notable for the abundance of these resource materials. Some units of Early Cretaceous age in Pike, Howard, and Sevier Counties contain significant beds of sand and gravel, especially the Pike Gravel and Ultima Thule Gravel Members of the Trinity Formation, which range in thicknesses from 20 to 100 feet and 0 to 40 feet, respectively. Units of Late Cretaceous age which contain abundant sand and gravel are the Woodbine, Tokio, and Nacatoch Formations. Sand and gravel deposits are present in the Woodbine Formation in Howard and Sevier Counties. The Tokio contains recoverable sand and gravel in Clark, Pike, Howard, and Sevier Counties. Sand beds are present in the Nacatoch Formation in Clark, Hempstead, and Howard Counties. Tertiary gravel deposits are abundant in interstream divides of the Gulf Coastal Plain in southern Arkansas and on Crowley's Ridge in northeast Arkansas. Gravel and sand deposits on Crowley's Ridge extend from St. Francis County northward to the Missouri state line. Extensive Quaternary alluvial deposits of sand and gravel are present in the major river systems in the state. Dredging operations in the rivers, especially the Arkansas River, recover significant amounts of sand and gravel. Also, deposits are present locally within or adjacent to the beds of the smaller rivers and streams in the state. Significant deposits of cherty clay and sandy regolith in North Arkansas are utilized for road and construction fill material. In these deposits, rock fragments vary from rounded to highly angular.

The Arkansas State Highway and Transportation Department sets specific standards relating to the performance of construction materials, for sand and gravel used in Arkansas' highway projects. Use of specific deposits of sand and/or gravel depends on the performance of these materials in standardized engineering tests, including, but not limited to, size distribution, abrasion resistance, grain shape (roundness), and percentage of admixed fines (silt or clay).

A list of the major uses for construction sand and gravel includes: concrete aggregate; concrete products, including block, brick, and pipe; aggregate in asphalt and other bituminous mixtures; road-base material and road coverings; construction fill; snow and ice control; filtration purposes; and railroad ballast.

Worldwide, more sand and gravel is mined annually than any other industrial raw material. Immense quantities of this resource are in Arkansas, and are currently mined in about 75 percent of the 75 counties. Preliminary estimates of sand and gravel production in Arkansas for 2005 by the U. S. Geological Survey are nearly 10.6 million metric tons valued at $62,000,000. Nearly 50 percent was used for concrete aggregate and concrete products. Large tonnages were also used for aggregate in asphalt (and other bituminous mixtures) and for road-base material and rural road coverings.

Arkansas State Highway and Transportation Department, 1993, Standard Specifications for Highway Construction, edition of 1993: Little Rock, 794 p.

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Sand, Industrial

Industrial sand is a high-purity quartz (SiO2) sand deposited by natural processes or sands that can be processed and upgraded to meet specialty use specifications.

In Arkansas, silica sand in economic quantities is present in the Ozark Plateau region in the St. Peter Sandstone (Early Ordovician) and some members of the Everton Formation (Ordovician). The most significant recovery of silica sand is from Unimin's underground mines developed in the St. Peter Sandstone at Guion, Izard County, where it is a pure orthoquartzite. A significant by-product is sand used as a filter material. The quartz sand grains of the St. Peter Sandstone in Arkansas are too angular to be usable for "frac" sand, due to secondary oriented silica growths. Annual production is withheld by the USGS to prevent disclosure of company proprietary data.

Sand dredged from the Arkansas River in west Arkansas is recovered and processed to produce a raw glass additive by Arkhola Sand and Gravel Company. Both industrial sand and construction sand are recovered. The feldspar-bearing sand is upgraded by classifying, drying, magnetic separation, and leaching processes, followed by a second drying. This yields a product containing ~6 percent feldspar. Arkhola's operational capacity is estimated at 850,000 tons per year of construction and industrial sand products. Other Arkhola industrial sand products include foundry casting sand, water filter sand, and "frac" sand for well development in the Fayetteville Shale play in central Arkansas. Total annual production is withheld by the USGS to prevent disclosure of company proprietary data.

The last production figures for industrial sand available for Arkansas are for 1994 and amounted to a total output of 684,000 metric tons of industrial sand, valued at $8.23 million.



Sandstone

Sandstone is a sedimentary rock composed mostly of sand-sized grains cemented by clay, silica, carbonate, or iron oxide. In most places, the majority of the constituent grains are quartz. Sandstone often contains other mineral grains such as feldspar or mica, and very small fragments of pre-existing rocks. When cemented by silica, sandstone has great strength, making it suitable for structural uses.

Most of the sandstone quarried in Arkansas is crushed and used for aggregate in concrete and asphalt. Large blocks (riprap) are used for fill and in dike and jetty construction. Rough, weathered sandstone blocks and boulders (fieldstone) have been used for years as facing stone on homes and other buildings, and to build other structures such as fireplaces, walls, and walkways. Much flaggy sandstone has been produced from the Hartshorne Sandstone (Pennsylvanian) near Midway in Logan County. Other counties in west-central Arkansas that occasionally produce this type of material are Logan, Sebastian, and Franklin. A substantial tonnage of thin flagstone and dimension stone has been produced in the state since the early 1950’s. A large quantity of natural or rough fieldstone used for rustic construction is obtained from bouldery talus and alluvial deposits throughout the Interior Highlands of Arkansas.

There are practically unlimited quantities of sandstone in the Paleozoic Highland area of Arkansas. An almost unlimited amount of this resource is present in the Boston Mountains and, to a lesser extent, in the Springfield and Salem Plateaus. The important sandstone units are principally in the lower Atoka Formation, Bloyd Shale, Hale Formation, Batesville Sandstone, St. Peter Sandstone, and Everton Formation. These sandstone-bearing units range in age from Ordovician to Pennsylvanian. The Arkansas Valley contains vast quantities of sandstone in the Savanna Formation, Hartshorne Sandstone, Atoka Formation, and Hale Formation (all Pennsylvanian). In the Ouachita Mountain region, sandstone is abundant in the Atoka Formation, Jackfork Sandstone, Stanley Shale, Blaylock Sandstone, Blakely Sandstone, and Crystal Mountain Sandstone. These formations range in age from Ordovician to Pennsylvanian.

Major aggregate quarries produce sandstone-based products near the larger cities and at other strategic sites in the Paleozoic Highlands of Arkansas.

Several criteria must be met to determine the best locations for prime aggregate, such as quality of available rock, closeness to market, and available transportation facilities (highways, barges, or railroads). Future demands for sandstone aggregate sources should continue to expand, notably near our larger communities, near and along the Arkansas River, and in the southern Ouachita Mountains. The nearby states of Louisiana, Mississippi, and Texas have been areas of major markets for high-quality Arkansas sandstone. Production of sandstone used for aggregate is included in the section on Crushed Stone.

Croneis, Carey, 1930, Geology of the Arkansas Paleozoic area with special reference to oil and gas possibilities: Arkansas Geological Survey Bulletin 3, 457 p.
Haley, B. R., Glick. E. E., Caplan, W. M., Holbrook, D. F., and Stone, C. G., 1979, The Mississippian and Pennsylvanian Systems in the United States – Arkansas: U. S. Geological Survey Professional Paper 1110-O, p. 1-14.
Hendricks, T. A., and Parks, Bryan, 1950, Geology of the Fort Smith District, Arkansas: U. S. Geological Survey Professional Paper 221-E, 94 p.
Miser, H. D., 1934, Carboniferous rocks of the Ouachita Mountains: American Association of Petroleum Geologists Bulletin, v. 18, p. 30-43.
Stone, C. G., and McFarland, J. D., III, with the cooperation of B. R. Haley, 1981, Field guide to the Paleozoic rocks of the Ouachita Mountain and Arkansas Valley Provinces, Arkansas: Arkansas Geological Commission Guidebook 81-1, 140 p.

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Shale / Slaty Shale

Shale

Shale is a sedimentary rock composed predominantly of clay-sized particles. Most of the particles are clay minerals, but other fine-grained clastic materials are normally present. Shale is formed by the lithification of clay or mud, commonly with admixed silt. Shales composed predominantly of clay minerals easily split into thin flat plates or sheets parallel to bedding (fissile). Arkansas shales, when freshly exposed, are commonly very dark gray or nearly black, but weather to shades of very light gray to buff. Black and gray shales owe their color to finely divided carbonaceous matter or pyrite. Less commonly, shale may be light gray, greenish, or reddish in color when fresh. Greenish shale owes it’s color to the presence of ferrous iron and/or chlorite, and reddish shale to the presence of iron oxide. Rock units consisting mostly of clay-sized particles of minerals other than clay are termed claystone or mudstone because they lack the fissility of shale.

Throughout most of the Interior Highlands, shale is the dominant sedimentary rock. Most shale occurs in very thick sequences of Mississippian and Pennsylvanian rocks. Units consisting almost entirely of shale may be more than 300 feet thick. Shale is more easily eroded than most other sedimentary rocks. Consequently, it underlies valley floors and the lower flanks of mountains where it is less likely to be exposed in outcrop than the more resistant sedimentary rocks occupying higher elevations. It is often exposed in creek beds, along the banks of the major rivers, and in road cuts.

Shale has several potential uses. It may be finely ground and used as a filler in paints, plastics, asphalt compounds, roofing cement, and some linoleum. In parts of Arkansas where clay is not locally available, shale is used to manufacture brick. Many county roads are based on shale and, if some harder aggregate such as thin-bedded sandstone or limestone is admixed, a relatively smooth and durable surface results. Shale is often used in paved highway construction as subbase fill material as it is readily available and less expensive to excavate than sandstone or limestone. Some shale units exhibit dramatic swelling when fired and have potential uses as lightweight aggregate. The Chattanooga Shale (Devonian) and younger black shales of the Ozark region of north Arkansas have not been investigated for oil shale potential. However, corresponding shale units in adjoining states yielded up to 15 gallons of oil per ton and averaged around 10 gallons per ton. Recovery was accomplished by distillation, instead of solvent extraction.

Shale, containing the mineral talc, developed from the alteration of shale adjacent to soapstone deposits in Saline County. Ground talcose shale has potential value as a filler in pottery clay. Baking of shale, which occurred in the zone of contact metamorphism at the Magnet Cove intrusion in Hot Spring County, created hornfels, a rock that is usable as a crushed stone product.

Slaty Shale

In parts of the Ouachita Mountains, especially the central core, much of the shale has undergone very low-grade regional metamorphism resulting in cleavage that has replaced fissility as the dominant planar structure. Cleavage permits the rock to be split easily into relatively thin slabs. The stone industry and many geologists this rock "slate." However, the degree of regional metamorphism is so low that other geologists prefer the term "slaty shale." Locally, in proximity to some major faults, shaly rocks have been sufficiently crystallized to be considered low-grade slate. The two types of rock can be used interchangeably for most purposes, but slaty shale has proven superior for roofing granules. Rough and cut blocks were previously used as shingles and for floors, patios, table tops, and interior and exterior covered walkways. This rock is good quality for interior applications, although most appears not to have undergone sufficient crystallization to stand up to prolonged exterior use.

The higher quality slaty shale in Arkansas is in portions of Polk, Montgomery, Garland, Pulaski, and Saline Counties. Deposits are in the Stanley Shale, Missouri Mountain Shale, Polk Creek Shale, Womble Shale, and Mazarn Shale formations (Paleozoic). Slaty shale in the Stanley Shale apparently has the best physical properties.

Deposits of Shale and Slaty Shale

Shale, used for local construction fill, has been mined from the Interior Highlands, and slaty shale from the core area of the Ouachita Mountains. Recent "slate" mining has been mostly restricted to Montgomery County. Slaty shale in the Stanley Shale north of Glenwood is hauled from the open pit to a preparation plant where it is crushed and ground into granules for roofing. Slaty shale of the Womble Shale was also mined from an open pit in northern Saline County. Broken rock was transferred to a grinding plant in Bryant. The rock was crushed, dried, ground, and bagged for rail shipment. It was used mainly as fillers and additives to paints and plastics. The company recently ceased operations in Arkansas.

Shale and slaty shale resources in Arkansas are considered inexhaustible. However, there can be shortages of particular types or colors. Markets for Arkansas slaty shale products are limited by competition from substitute materials and the relatively few industries utilizing slate granules and flour (fines).


Branner, G. C., 1940, Mineral resources of Benton, Carroll, Madison, and Washington Counties: Arkansas Geological Survey County Mineral Report 2, 55 p.
Miser, H. D., and Purdue, A. H., 1929, Geology of the DeQueen and Caddo Gap quadrangles, Arkansas: U. S. Geological Survey Bulletin 808, 195 p.
Nuelle, L. M., and Sumner, S. S., 1981, A preliminary evaluation of shale-oil resources in Missouri: Missouri Department of Natural Resources, Division of Geology and Land Survey, Information Circular 27, 31 p.
Purdue, A. H., 1909, The slates of Arkansas: Arkansas Geological Survey, 170 p.
Purdue, A. H., and Miser, H. D., 1923, Description of the Hot Springs district: U. S. Geological Survey Atlas, Folio 215, 12 p.
Stone, C. G., and Bush, W. V., 1984, General geology and mineral resources of the Caddo River watershed: Arkansas Geological Commission Information Circular 29, 32 p.
Swanson, V. E., 1960, Oil yield and uranium content of black shales: U. S. Geological Survey Professional Paper 356-A, 44 p.

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Silica Pebble

Silica pebble is a relatively new application of white to gray silica gravel. Several size ranges are available and, depending upon the size, applications include loose decorative gravel, and decorative driveways and pool decks where it is embedded in epoxy resin over concrete. Very high silica white pebble is crushed and finds applications in decorative gunite in swimming pools and as white roofing granules. Sheridan White Rock Company in Grant County, Arkansas, produces both bagged and bulk shipped silica pebble. Their mine is located 11 miles south of Sheridan. Production is withheld to avoid disclosing company proprietary data.

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Soapstone / Talc

Soapstone deposits in Arkansas were first discovered in 1888. The massive soapstone typically consists of 50 to 80 percent talc (Mg3Si4O10(OH)2) admixed with chlorite, serpentine, pyrite, quartz, calcite, magnesite, and dolomite. The rock is either massive or flaky depending on the talc and chlorite content. It is soft and has a slightly greasy or dry soapy feel when rubbed on the hands. Soapstone and talc are usually associated and are generally grouped together.

Beginning in 1953, Milwhite, Inc. operated soapstone mines at various open pits along a narrow 4-mile-long belt in northeastern Saline County and processed the rock at a grinding plant at Bryant, Saline County. The soapstone was crushed, dried, ground to a fine powder, passed through a cyclone separator, and bagged. Most Arkansas production was used as inert fillers and in vehicle brake shoes. Mine output averaged about 1,500 short tons of soapstone annually. The company permanently closed their mine and plant operations in 1999, principally due to being included as a raw materials supplier in asbestos lawsuits, even though it has never been proven that any carcinogenic mineral was a component of Arkansas soapstone.

The soapstone-serpentine deposits are probably Precambrian in age and exist as exotic lenses or masses in shale and chert beds of Ordovician age. They were most likely injected into the younger rocks by tectonic processes. Because the serpentine pinches and swells in breadth and winds sinuously, lenses of soapstone appear as isolated bodies, though in places they may join at depth. Evidence suggests that the 5 mined deposits contained more than 500,000 tons of soapstone in total initially, of which some 69,000 short tons were mined.

Cox, T. L., 1988, Tectonically emplaced serpentinites of the Benton uplift, Saline County, Arkansas, in Colton, G. W., ed., Proceedings of the 22nd Forum on the Geology of Industrial Minerals: Arkansas Geological Commission Miscellaneous Publication 21, p. 49-61.
Sterling, P. J., and Stone, C. G., 1961, Nickel occurrences in soapstone deposits, Saline County, Arkansas: Economic Geology, v. 56, p. 100-110.
Stone, C. G., and Sterling, P. J., 1964, Relationship of igneous activity to mineral deposits in Arkansas: Arkansas Geological Commission Miscellaneous Publication 8, 23 p.
Wicklein, P. C., 1957, Geology of the nickeliferous soapstone deposits of Saline County, Arkansas: Columbia, University of Missouri, M. S. thesis, 68 p.

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Stone, Crushed

Crushed stone is any rock that has been broken by mechanical means into smaller fragments. The output from the crushing process is usually screened to separate the material into different size categories, ranging from dust to boulders. The use of crushed stone in construction depends on the type of stone and its physical characteristics as determined by using standard engineering tests. Although crushed stone is utilized in a wide variety of applications, the construction industry utilizes some 80 percent of mine output.

Nepheline syenite, limestone/dolostone, sandstone, quartzite, novaculite, slate, and volcanic tuff are the major types of stone that have been quarried and utilized in Arkansas as crushed stone. Of this list, novaculite is no longer used due to its highly abrasive effects on crushing equipment and problems concerning its use as an aggregate in asphalt. Transportation costs to a specific job site are a major economic consideration when determining whether to use rock from any given quarry. Currently, all of these rock types are mined from open pits.

In 2005 total production and value of crushed stone construction aggregates from Arkansas amounted to 35.4 million metric tons and $223 million, up significantly in recent years. Each particular rock type is discussed briefly below.


Nepheline Syenite
Much of Arkansas' nepheline syenites have high strength and weather-resistant properties and are crushed for use as roofing granules, road materials, riprap, and asphalt and concrete aggregate. Fines are used as a colorizing and fluxing agent in the manufacture of brick and as compaction fill. Historically, this rock has been used as a building, monument, and paving stone and for railroad culvert and bed construction. Syenite was also used extensively as riprap for the protection of river banks and road embankments. Arkansas' syenite deposits have been studied as a potential source of the mineral nepheline, which is used in the manufacture and fabrication of glass. However, the inclusion of various fine-grained iron-bearing minerals in this mineral results in too high of an iron value to manufacture low-iron glass. The development of new separation technology may allow the use of Arkansas nepheline concentrates for specialty markets. Several syenite deposits have been examined for potential use as low free-silica (minimal quartz) sand-blast abrasive. Federal government form listings term the rock as granite for regulators.

Nepheline syenite and its associated igneous rocks are exposed in 4 areas of the state: south-central Pulaski County between Little Rock and Sweet Home, Saline County in the vicinity of Bauxite, Garland County at Potash Sulphur Springs, and Hot Spring County at Magnet Cove. The total surface exposure of syenite in Arkansas is about 13 square miles.

Nepheline syenite is quarried at Granite Mountain in Pulaski County by several companies. It is crushed and sized for several aggregate uses. Crushed, sized roofing granules, colorized to builder’s specifications, are produced at a plant east of Little Rock, using syenite from a nearby quarry. Nepheline syenite has also been quarried near Bauxite in Saline County and at the Diamond Jo quarry in Magnet Cove, Hot Spring County. Presently, one company is producing nepheline syenite from a quarry near Bryant in Saline County. Mining of nepheline syenite exceeds 5 million short tons annually.

Limestone/Dolostone
All of the dolostone and most of the limestone in Arkansas are Paleozoic in age and are present in the Ozark region. A small amount of Paleozoic limestone in the Ouachita Mountains has been quarried.

Often, little distinction is made between limestone and dolostone because they are often interchangeable in their uses. Both are frequently sold under the name of limestone. Perhaps no other mineral resource has as many uses as limestone and dolostone. These two rocks are the basic building blocks of the construction industry. The principal aggregate uses are as crushed stone, riprap, asphalt fillers, and road fill material.

Crushed limestone, used largely as concrete and asphalt aggregate, is the major product of limestone/dolostone mining in Arkansas. Several companies in Benton, Independence, and Lawrence Counties mine and crush the stone. The bulk of the crushed material is used in road construction and concrete aggregate. In 2005, 1 dolostone and 27 limestone quarries were active, with total production of 13.5 million short tons, valued at 81.7 million.

Sandstone/Quartzite
Most of the sandstone quarried in Arkansas is crushed and used for aggregate in concrete and asphalt. Large blocks (riprap) are used for fill and in dike and jetty construction.

There are practically unlimited quantities of sandstone in the Paleozoic Highland area of Arkansas. An almost unlimited amount of this resource is present in the Boston Mountains and, to a lesser extent, in the Springfield and Salem Plateaus. The important sandstone units are principally in the lower Atoka Formation, Bloyd Shale, Hale Formation, Batesville Sandstone, St. Peter Sandstone, and Everton Formation. These sandstone-bearing units range in age from Ordovician to Pennsylvanian. The Arkansas Valley contains vast quantities of sandstone in the Savanna Formation, Hartshorne Sandstone, Atoka Formation, and Hale Formation (all Pennsylvanian). In the Ouachita Mountain region, sandstone is abundant in the Atoka Formation, Jackfork Sandstone, Stanley Shale, Blaylock Sandstone, Blakely Sandstone, and Crystal Mountain Sandstone. These formations range in age from Ordovician to Pennsylvanian.

Major aggregate quarries produce sandstone-based products near the larger cities and at other strategic sites in the Paleozoic Highlands of Arkansas.

Future demands for sandstone aggregate sources should continue to expand, notably near our larger communities, near and along the Arkansas River, and in the southern Ouachita Mountains. The nearby states of Louisiana, Mississippi, and Texas have been areas of major markets for high-quality Arkansas sandstone. In 2005, 18 quarries produced 10.5 million metric tons of crushed sandstone and quartzite, valued at $67.4 million.

Slatey Shale/Metamorphosed Shale and Sandstone
Slaty shale is mined from the core area of the Ouachita Mountains by Certain Teed Corporation. Early operations in the 1920s centered on Ordovician age slatey shales for roofing tiles, but they did not hold up to weather conditions in their markets and closed a few years after startup. Recent "slate" mining has been mostly restricted to Montgomery County. Slaty shale in the Stanley Shale (Mississippian), north of Glenwood, is hauled from Certain Teed’s open pit to a preparation plant where it is crushed and ground into granules for roofing. The final product is black.

Martin Marietta Materials Company produces aggregates for asphalt mix at their Jones Mill quarry near Magnet Cove in Hot Spring County. The rock is contact metamorphosed sandstone and shale of the Stanley Shale (Mississippian), adjacent to the Magnet Cove intrusive complex. The company also has an asphalt plant on site. Production is withheld by the USGS to avoid disclosing proprietary company data.

Tuff
In Arkansas, the Hatton tuff lentil of the Stanley Shale (Mississippian) is exposed in Polk County. Southwest of the community of Hatton, the tuff has a maximum thickness of 300 to 400 feet, but 90 feet is more common. Increased thickness is due to repetitive reverse faulting at the quarry location. The tuff is massive, homogeneous, and jointed so that determination of bedding is difficult. The unweathered fine-grained rock is dark greenish gray and may appear spotted due to light-colored feldspar crystals. Under the microscope, numerous broken volcanic glass fragments (shards) compose much of the rock. The unweathered rock is tough, compact, and may contain Late Pennsylvanian milky quartz veins.

The Hatton tuff is now used in Arkansas as an aggregate as fresher portions of the deposits are mined by Martin Marietta Materials Company. It was previously shipped to and continues to be an available concrete aggregate resource for east Texas. The Hatton also has potential as a cementing agent. Annual production is included in miscellaneous crushed stone by the USGS to avoid disclosing company proprietary data.

U. S. Geological Survey in cooperation with the  Arkansas Geological Commission, 2000, Arkansas 1999 annual estimate: U. S. Geological Survey Mineral Industry Surveys, 6 p.
White, D. H., Jr., and Bush W. V., 1991, The mineral industry of Arkansas, in US Geological Survey Mineral Industry Surveys, Arkansas: p. 89-98.

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Stone, Dimension

Dimension stone is rock that was removed from its original site to be used (fieldstone) and rock that was broken, sawn, and/or ground and polished (processed) for use as building and/or ornamental stone. While most of the high-quality stone produced in Arkansas is used in-state, some is shipped to markets worldwide. Limestone and sandstone are used as dimension stone in Arkansas.

Some dimension-stone operations can produce blocks of stone weighing up to about 9 tons. Such large blocks require specialized equipment for extraction and transportation. The manufacture of building stone remains a labor intensive industry. A finished piece of building stone is an expensive product due to extra labor costs. This means that a piece of stone which has been highly worked/or polished costs more than a partially finished or rough block. Dimension stone may be sold as rough block, sawn slabs, or finished product. Flaggy sandstone is mined by ~12 companies in Arkansas, the predominance of sandstone production being from the Hartshorne and Atoka Formations (Pennsylvanian) in the western Arkansas Valley in Sebastian, Franklin, Logan, and Van Buren Counties. Flaggy sandstone is also produced by one company in Stone County in north central Arkansas from the Atoka Formation. Ordovician age limestone/dolostone and Mississippian age limestones and sandstones of Independence County are mined and processed for both interior and exterior use by Oran McBride Stone Company. Ordovician age dolostone from the Cotter Formation of Carroll County is mined and processed for exterior use by Johnson’s Landscaping & Construction LLC. Eureka Stone Company, also of Carroll County, produces exterior and interior finished stone products from stone furnished by Johnson’s quarry.

Production figures have been withheld since 1966 to avoid disclosing company proprietary data. However, the current total annual production of Arkansas dimension stone is estimated by the AGS to be approximately 100,000 tons valued at $8.5 million.

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Sulfur

Sulfur (S) is a pale yellow nonmetallic element with a low melting point and low specific gravity (~2.0). Sulfur is used in the manufacture of chemical fertilizer. Numerous industrial applications arise from conversion of sulfur to sulfuric acid.

A source of sulfur for early pioneers was the mineral pyrite (FeS2). Sulfur was important because of its use in black powder (gun powder). During the Civil War, a deposit of pyrite at Magnet Cove was investigated by the Confederacy as a source of sulfur. A pyrite deposit near Berryville in Carroll County was explored during 1937 and 1938 as a possible source of sulfur. The pyrite is in a highly fractured zone of the Cotter Formation (Ordovician). This deposit contains 482,000 long tons of ore ranging in grade from 6.5 to 32.4 percent sulfur, averaging 24.3 percent. A second major resource of sulfur is the gypsum deposits of Pike and Howard Counties in southwest Arkansas. Presently, processed sulfur from other sources is so inexpensive, the development of commercial sulfur from gypsum is not feasible.

The first experimental plants in the United States for the recovery of sulfur from natural gas were located in Columbia and Lafayette Counties in Arkansas. Analyses of oil field gases were first published in 1940 and helped bring attention to this resource. Pilot plants built in 1941 led to the construction of two full-scale production facilities, one in each county, in 1943. The Columbia County plant served the Dorcheat-Macedonia field for about 15 years and was dismantled and moved to Texas in 1958. In the Dorcheat-Macedonia area, the hydrogen sulfide content of natural gas was as high as 2,400 grains per 100 cubic feet. The Columbia County plant had a production capacity of 10 long tons per day of free sulfur. The plant in Lafayette County served the McKamie field. The gas from the McKamie field contained as much as 4,500 grains of hydrogen sulfide per 100 cubic feet of natural gas. This "sour" gas was purified to a hydrogen sulfide content of 0.05 grains per 100 cubic feet in the pilot-plant operation. The ensuing commercial plant was producing 65 tons of free sulfur daily by the end of 1943 and recovering 97 percent of the sulfur in the gas. In 1960, the McKamie facility had a production capacity of 110 long tons per day and is presently in operation.

The start of full-scale operations in the McKamie field marked the initial use of the Claus process for sulfur recovery in the United States, which was the first process for recovering sulfur from hydrogen sulfide. The Claus process involves burning one-third of the hydrogen sulfide to form sulfur dioxide, which then reacts with the unburned hydrogen sulfide in the presence of a surface-active catalyst to form sulfur and water vapor. The sulfur is condensed to liquid form and shipped or stored in that manner, or is allowed to solidify for handling as a solid.

Prior to the development of sulfur-extraction units, natural gas containing appreciable amounts of hydrogen sulfide was flared because of its corrosive nature and unpleasant odor. If used as a boiler fuel, gas may contain as much as 360 grains of hydrogen sulfide per 100 cubic feet and still not be too objectionable. However, natural gas used for domestic purposes is not permitted to contain more than 1.5 grains of hydrogen sulfide per 100 cubic feet.

Sulfur has been produced by one petroleum refinery in Union County for years. The source of the sulfur is gas freed at the refinery during the production of other petroleum products. Production capacity was rated at 10 long tons per day in 1960. In 1984, a company near Magnolia, Columbia County, began recovering sulfur during bromine extraction and continues today.

Blade, O. C., and Branner, G. C., 1940, Survey of crude oils of the producing fields of Arkansas: U. S. Bureau of Mines Report of Investigations 3486, 40 p.
Grandone, Peter, and McHarg, R. E., 1952, Oil, gas, and sulfur in the Arkansas and Red River basins, Arkansas: U. S. Inter-agency Committee on Arkansas-White-Red River Basins, Minerals and Geology Workgroup, Preliminary Report, 12 p.
Netzeband, F. F., Early, T. R., Ryan, J. P., and Miller, W. C., 1964, Sulfur resources and production in Texas, Louisiana, Missouri, Oklahoma, Arkansas, Kansas, and Mississippi, and markets for the sulfur: U. S. Bureau of Mines Information Circular 8222, 77 p.

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Tripoli

Tripoli is a microcrystalline form of quartz (SiO2) which is derived by the alteration of chert, chalcedony, or novaculite, or leaching of highly siliceous limestones. Tripoli has numerous applications, mainly as an abrasive in polishing, buffing, and burnishing compounds, in scouring soaps and powders, and recently, as a filler or extender in plastics, rubber, in sealants and epoxy resins, and as a pigment in paints. Firing tests on tripoli blocks have shown its potential as a high-quality lightweight aggregate.

Tripoli is present in 3 general areas of Arkansas: northwestern Arkansas near Rogers in Benton County; in the Ouachita Mountains near Hot Springs in Garland County; and near Athens in Howard County.
The deposits of northwestern Arkansas were formed by the weathering of cherty limestones of the Boone Formation (Mississippian), while the Ouachita Mountains deposits were formed by the leaching of a limy phase within the Upper Division of the Arkansas Novaculite (Mississippian). Originally, portions of the Upper Division contained as much as 30 percent carbonate. Tripolitic zones in the Bigfork Chert (Ordovician) in western Saline County were investigated for commercial potential and are now being utilized.

Analyses of Arkansas tripoli reveal that silica content is greater than 99 percent. A typical analysis of processed tripoli from Arkansas novaculite is 99.49 % SiO2, 0.0l5 % TiO2, 0.102 % Al2O3, 0.039 % Fe2O3, 0.021 % MgO, and 0.014 % CaO, for a total of 99.68 %. Although all 3 areas have been mined, there only one mine and processing facility is presently active. Malvern Minerals Company of Hot Springs in Garland County markets their products under registered trade names. Tripoli has been mined by both underground (Ozark region) and open-pit (Ouachita region) methods. The mined material is dried, crushed, pulverized, disaggregated, and sized by screening or air-flotation. The range of particle size of individual quartz grains composing tripoli is from 0.5 to 10 microns and equidimensional. The color of the tripoli varies within the same deposit. Colors include white, cream, tan, and brown, with white being the least prevalent, but most marketable.

The mined output of tripoli usually amounts to about 15,000 short tons per year. In 2005, Arkansas ranked 3rd in the nation out of 4 producing states. Reserves of higher-grade white tripoli are limited, but other color grades are several million tons.

Griswold, L. S., 1892, Whetstones and the novaculites of Arkansas: Arkansas Geological Commission Survey Annual Report for 1890, v. III, 443 p.
Holbrook, D. F., and Stone C. G., 1978, Arkansas Novaculite – A silica resource, in Johnson, K. S. and Russell, J. A., eds., Thirteenth Annual Forum on the Geology of Industrial Minerals: Oklahoma Geological Survey Circular 79, p. 51-58.
Keller, W. D., Stone, C. G., and Hoersch, A. L., 1985, Textures of Paleozoic chert and novaculite in the Ouachita Mountains of Arkansas and Oklahoma and their geological significance: Geological Society of America Bulletin, v. 96, p. 1353-1363.
Steuart, C. T., Holbrook, D. F., and Stone, C. G., 1984, Arkansas Novaculite: Indians, whetstones, plastics, and beyond, in McFarland, J. D., III, and Bush, W. V., eds., Contributions to the geology of Arkansas, v. II: Arkansas Geological Commission Miscellaneous Publication 18-B, p. 119-134.

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Tuff

Tuff is a pyroclastic rock composed mostly of angular fragments of volcanic material deposited from the air. If deposited on land while hot, the particles weld together as a welded tuff; otherwise, normal lithification occurs.

In Arkansas, two tuff units are present. The Hatton tuff lentil of the Stanley Shale (Mississippian) is exposed in Polk County. Southwest of the community of Hatton, the tuff has a maximum thickness of 300 to 400 feet, but 90 feet is more common. The tuff is massive, homogeneous, and jointed so that determination of bedding is difficult. The unweathered fine-grained rock is dark gray and may appear spotted due to light-colored feldspar crystals. Under the microscope, numerous broken volcanic glass fragments (shards) compose much of the rock. The unweathered rock is tough, compact, and may contain Late Pennsylvanian milky quartz veins. Tuff beds are also present in southwest Arkansas in the Woodbine Formation (Cretaceous), but have no resource potential for aggregate.
The Hatton tuff has now begun to see use in Arkansas as an aggregate as fresher portions of the deposits near Hatton, Polk County, are mined.   It was previously shipped to and continues to be an available concrete aggregate resource for east Texas.   The Hatton also has potential as a cementing agent.

Honess, C. W., 1923, Geology of the southern Ouachita Mountains of Oklahoma: Oklahoma Geological Survey Bulletin 32, part 1, 278 p.
Miser, H. D., and Purdue, A. H., 1929, Geology of the DeQueen and Caddo Gap quadrangles, Arkansas: U. S. Geological Survey Bulletin 808, 195 p.
Williams, J. F., 1891, The igneous rocks of Arkansas: Arkansas Geological Survey Annual Report for 1890, v. II, 457 p.

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Vermiculite

Vermiculite is a mica-like silicate mineral of the general formula (Mg,Fe2+,Al)3(Si,Al)4O10 (OH)2 . 4H2O that rapidly expands upon heating, resulting in a low-density material. The expanded material is used as a lightweight aggregate and insulation in the construction industry, a carrier for fertilizers and a soil conditioner in agriculture, a fragrance carrier, and a filler and texturizer for plastics and rubber.

Vermiculite was observed during mining of iron ore in the 1940’s and 1950’s at Magnet Cove, Hot Spring County. Residual flake vermiculite originated from the iron-rich mineral biotite in igneous rock, then processes of alteration and weathering created vermiculite. These deposits have unknown commercial potential. Exploration for vermiculite deposits is straightforward since they are the products of surface and near-surface weathering processes.

Although Arkansas does not have any vermiculite mining operations, companies in Arkansas expand imported vermiculite, placing Arkansas among the principal expanded-vermiculite producing states in the United States.

Erickson, R. L., and Blade, L.V., 1963, Geochemistry and petrology of the alkalic igneous complex at Magnet Cove, Arkansas: U. S. Geological Survey Professional Paper 425, 99 p.
Williams, J. F., 1891, The igneous rocks of Arkansas: Arkansas Geological Survey Annual Report for 1890, v. II, 457 p.

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Wollastonite

Wollastonite (CaSiO3) is a mineral which can develop as skarn deposits (in contact metamorphic situations) and as a primary magmatic mineral (associated with carbonatites). The mineral cleaves into particles with needle-like shapes, having great strength. Wollastonite is a high-performance mineral filler in paint, plastics, and thermal board; it also is a substitute for asbestos and an additive to ceramics, where it imparts strength and rapid firing, and inhibits shrinkage and warping. The mineral has several unique properties which create continued growth in its demand. Wollastonite reduces energy costs when used to replace sand and limestone in glass and glass fiber by lowering the fusion temperature. Surface-modified wollastonite powders in fine and ultrafine grades are used increasingly as plastic filler.

In Arkansas, wollastonite formed along the contact zone of the Potash Sulphur Springs igneous intrusion and the Arkansas Novaculite, where carbonate-rich fluids from the intrusion reacted with silica-rich novaculite. There has been no mining of wollastonite from Arkansas and the known deposits have not been commercially evaluated. Resources are limited, to one location, but wollastonite could be a by-product if the host rock was processed for other mineral value.

Milton, Charles, 1984, Miserite, a review of world occurrences with a note on intergrown wollastonite, in McFarland, J. D., III, and Bush, W. V., eds., Contributions to the geology of Arkansas, v. II,: Arkansas Geological Commission Miscellaneous Publication 18-B, p.97-114.
Williams, J. F., 1891, The igneous rocks of Arkansas: Arkansas Geological Survey Annual Report for 1890, v. II, 457 p.

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Arkansas Geological Survey
Vardelle Parham Geology Center
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Little Rock, AR 72204
Phone: 501-296-1877 | Fax: 501-663-7360
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