AGS / Minerals / Industrial / Descriptions A - D
Asphalt is a brown to black, high viscosity liquid or bitumen that consists almost entirely of carbon and hydrogen and has a low melting temperature. Natural asphalts form in oil-bearing rocks by evaporation of the volatiles. Asphalt has a low specific gravity and burns with a bright, hot flame. Asphalt is used for road surfacing, as a filler for joints in concrete, as a dust preventive, for roofing and water-proofing, in the rubber industry, in asphalt-based paints, and in the manufacture of asphalt flooring tile.
Asphaltic sand and gravel deposits are present in the Trinity Group (Cretaceous) in Pike and Howard Counties. Most deposits are very small, but may range up to 12 feet in thickness. Between 1900 and 1906, asphaltic sands were mined from open pits about 2.5 miles south of Pike in Pike County. Some 4,815 tons of asphaltic sand, valued at $22,368, was mined and shipped to Little Rock for use in street paving.
Essentially all asphalt now used in Arkansas consists of crude oil residues left over from the production of other petroleum products at refineries. None of the asphalt deposits in the state are presently being mined.
Hayes, C. W., 1903, Asphalt deposits of Pike County, Arkansas: U. S. Geological Survey Bulletin 213, p. 353-355.
Miser, H. D., and Purdue, A. H., 1918, Asphalt deposits and oil conditions in southwestern Arkansas: U. S. Geological Survey Bulletin 691, p. 271-292.
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.
Production of barite from Arkansas was used exclusively as a weighting agent in drilling muds in the oil and gas industry, due to its relatively high specific gravity (4.5). World class barite deposits contained within the Stanley Shale (Mississippian) are present in the Ouachita Mountains province of Arkansas, specifically in Hot Spring, Montgomery, and Polk Counties. Production was mainly by National Lead Division of Baroid Company and Magnet Cove Barium Corporation (Magcobar).
In 1981, the cost of extracting and processing barite ore exceeded the product's value because the nation began importing ore from less expensive over-seas sources. Most of the barite mining operations in the United States ceased.
Mining and Production
Most of Arkansas' bedded deposits were worked solely by open-pit methods, but the Chamberlain Creek deposit in Hot Spring County was mined by both open-pit and underground techniques. Ore in the deeper parts of the syncline was mined underground to as much as 500 feet below the ground surface. Most of the barite was processed at flotation mills at Magnet Cove and Malvern, both in Hot Spring County. A small quantity of barite ore was mined and test-milled by Milchem Corporation at Hopper, Montgomery County, before economics forced closure of the facility. The flotation mills typically utilized barite ore containing about 50 percent barite. The result was a concentrate composed of 92 to 94 percent barite. Total production of Arkansas barite concentrates is 9 million short tons (1939-1983 inclusive) – 8 million short tons from the Chamberlain Creek deposit alone valued at ~ 70 million dollars.
Reserves of barite in Arkansas are estimated to be in the order of millions of tons, but further mining awaits barite's expanded use. Increased domestic oil-field drilling activities and a shortage of cheap foreign ores could make Arkansas barite a viable mineral commodity again.
Hanor, J. S., and Baria, L. R., 1977, Controls on the distribution of barite deposits in Arkansas, in Stone, C. G., ed., Symposium on the geology of the Ouachita Mountains, v. 2: Arkansas Geological Commission Miscellaneous Publication 14, p. 42-47.
Jones, T. A., 1948, Barite deposits in the Ouachita Mountains, Montgomery, Polk, and Pike Counties, Arkansas: U. S. Bureau of Mines Report of Investigations 4348, 15 p.
Mitchell, A. W., 1984, Barite in the western Ouachita Mountains, Arkansas, in Stone, C. G. and Haley, B. R., eds., Guidebook to the geology of the central and southern Ouachita Mountains, Arkansas: Arkansas Geological Commission Guidebook 84-2, p. 124-131.
Scull, B. J., 1958, Origin and occurrence of barite in Arkansas: Arkansas Geological and Conservation Commission Information Circular 18, 101 p.
Zimmerman, R. A., 1965, The origin of the Arkansas bedded barite deposits with special reference to the genetic value of sedimentary features in the ore: Ph. D. dissertation, Rolla, University of Missouri, 367 p.
The principal ore of aluminum is bauxite, a complex mixture of a number of aluminum hydroxides and hydrous aluminum oxides. The most common aluminum-bearing minerals in bauxite are gibbsite (AlOH3), boehmite (AlO(OH)), and diaspore (AlO(OH)). In the Arkansas deposits, diaspore has not been reported. Free quartz along with iron and titanium oxides are common components. Bauxite ranges in color from off-white to deep reddish brown, and structurally from a soft earthy material to a well-cemented rock.An easily recognizable oolitic (BB-sized concretions) to pisolitic (pea-sized concretions) grain texture characterizes many bauxite deposits, including those in Arkansas. Commercial bauxite usually has a minimum content of 50 to 55 percent alumina (Al2O3).
In the bauxite refining process, the aluminum-bearing minerals in bauxite are converted in a multiple-step process to alumina (Al2O3). Alumina can be smelted to form metallic aluminum or it can be used as the source of many other products, including refractory materials used to line high-temperature rotary kilns and metallurgical furnaces. In addition, alumina is a source of many chemicals used in the paper and ceramic industries, in petroleum refining, and in some water-purification processes. Other significant uses include the production of synthetic corundum for the manufacture of abrasive stones and grinding wheels, as propants in the petroleum-production industry, and as an ingredient in deodorants, antacids, and some medicines.
The Arkansas bauxite region covers about 275 square miles in the northern part of the West Gulf Coastal Plain and is divided into two mining districts. One area is in Pulaski County south and east of Little Rock and the other is in nearby Saline County, northeast and east of Benton. The bauxite is present mostly as sheet or blanket deposits in very close proximity to outcrops of the intrusive igneous rock, nepheline syenite. The deposits formed in early Tertiary time, developing as soils along the western edge of a shallow marine basin that occupied the Mississippi River Embayment. During that time, hills and knobs of syenite as islands were exposed to intense chemical weathering in a tropical or near-tropical environment (lateritic weathering). In the weathering process, leaching by rain, ground water, and perhaps by salt spray, decomposed the original igneous rock minerals (feldspar and nepheline), removed much of the silica, and concentrated the newly formed oxides and hydroxides of aluminum as the rock we term bauxite. These are residual deposits because they formed essentially in place (in situ paleo-soils). Many other deposits, generally smaller, consist of bauxite removed by erosion from its site of origin and redeposited nearby (transported deposits).
Mining of bauxite for metal production began in 1898 and was continuous for that purpose until 1982. Because of changing domestic and world economic market conditions, 1982 was the last year in which bauxite was mined in Arkansas for aluminum metal. Small tonnages continue to be mined and used in the production of a variety of alumina-based materials, including various chemicals, abrasives, and propants. Arkansas continues to be the nation’s leader in bauxite production, most ore processed in the USA being imported.
Bramlette, M. N., 1936, Geology of the Arkansas bauxite region: Arkansas Geological Survey Information Circular 8, 68 p.
Canby, T. Y., 1978, Aluminum, the magic metal: National Geographic, v. 154, no. 2, p. 186-211.
Gordon, MacKenzie, Jr., Tracey, J. I., Jr., and Ellis, M. W., 1958, Geology of the Arkansas bauxite region: U. S. Geological Survey Professional Paper 299, 268 p.
Elemental bromine (Br) is a highly corrosive, reddish-brown, volatile liquid which, along with fluorine, chlorine, and iodine, forms a family of elements known as the halogens. About 85 percent of the bromine recovered is consumed at the production site by the bromine producers. Major products include fire retardants, ingredients in bug and fungus sprays, antiknock compounds in leaded gasoline, and oil-well completion fluids. The remainder, as elemental bromine, is shipped to various chemical processors for use in chemical reagents, disinfectants, photographic preparations and chemicals, solvents, water-treatment compounds, dyes, insulating foam, and hair-care products.
Bromine and iodine are extracted from sea water by seaweed and plankton. In Arkansas, decomposition of organic debris during the Jurassic Period released both bromine and iodine to the forming brines. However, iodine is thought to have escaped from the system into the atmosphere through the process of oxidation. During the processes that produced the hydrocarbons composing petroleum and natural gas, bromine became even more concentrated in the associated salt brines. In Arkansas, it is thought that brines in the Louann Formation migrated through the overlying Norphlet Formation into the Smackover Formation.
Bromine is present in abnormally high concentrations in salt brines of the Smackover Formation (Jurassic) in south-central Arkansas. The original analyses that led to the development of Arkansas' bromine industry were performed by the Arkansas Geological Commission chemist on brines from 4 oil fields developed in the Smackover Formation. The analyses showed bromine concentrations ranging from 4,000 to 4,600 parts per million, or about 70 times the bromine concentration of normal ocean water. Between 1.5 to 1.8 pounds of bromine are recovered from every barrel of brine processed.
The first commercial recovery of bromine in Arkansas was from Union County in 1957, and production has been continuous ever since. Arkansas' industry continues as the world's leading producer of bromine, averaging 40 percent of the world's production for the 5-year period between 1986 and 1990, inclusive. During the same period, the average rate of growth of Arkansas' bromine recovery was more than 20 million pounds per year. U. S. production in 2001 was 212,000 metric tons, valued at $159 million, with Arkansas' output accounting for 97 percent. U. S. Geological Survey data for 2005 indicate that 27 percent of Arkansas' non-fuels mineral value was due to bromine recovery. Bromine presently is recovered from brines in Columbia and Union Counties. In 2006, Arkansas, with six plants operated by Albemarle and Chemtura Corporation (locally known as Great Lakes Chemical Company), again led the Nation in bromine production, and bromine was the leading mineral commodity in terms of value produced in the State.
In 2006, Tetra Technologies Inc. announced plans to invest $100 million in a project to produce bromine from brine. The plant will process bromine, calcium chloride, and sodium chloride from brine reserves around Magnolia, AR. The bromine produced would replace bromine now being imported and would have negligible effect on current producers.
In Arkansas, chalk is the major constituent of two extensive Cretaceous formations: the Annona Chalk and the Saratoga Chalk. These sedimentary deposits are exposed in a trend extending northeasterly from Foreman in Little River County to Arkadelphia in Clark County and dip gently to the south-southeast. Of these two formations, only the Annona has had commercial production.
The Annona Chalk is a hard, white, thick-bedded, massive chalk containing few macrofossils. It is exposed 2.5 miles north of Columbus in Hempstead County westward to Foreman, for about 35 miles across Hempstead, Howard, and Little River Counties. North of Columbus, the chalk is less than 1 foot thick and pinches out to the east. The best exposures of the Annona Chalk are in the vicinity of Foreman and at White Cliffs Landing on the Little River, both in Little River County. At White Cliffs Landing, the chalk has a maximum exposed thickness of about 100 feet.
In 1929, a cement-manufacturing plant was erected in southwest Arkansas near Saratoga. A second plant was built near Foreman in 1958. Both mined the Annona chalk from open pits. The plant near Saratoga closed in the early 1990’s after about 60 years of operation. The mine has now been reclaimed and became part of Millwood Lake. For a brief period, the Annona chalk also was mined by open-pit methods at White Cliffs Landing for cement and whiting, but the chalk proved to contain too much silica and mining ceased. In 1969, the Arkansas Geological Commission and the U. S. Bureau of Mines, using outcrop data, calculated chalk reserves of 700 million tons in the Annona Chalk in Sevier and Howard Counties.
Chalk, used for the manufacture of cement, continues to be mined near Foreman by Ash Grove Cement Company. The plant near Foreman is presently the 28th largest facility by capacity in the United States. In 2007 plans were announced for the replacement of the existing plant by a new $350 million plant, with an increase in production from 1 million tons/year to 1.7 million tons/year. Ash Grove Cement is the largest American owned cement company in the USA.
Branner, J. C., 1898, The cement materials of southwest Arkansas: American Institute of Mining Engineers Transactions, v. 27, p. 42-63.
Dane, C. H., 1929, Upper Cretaceous formations of southwestern Arkansas: Arkansas Geological Survey Bulletin 1, 215 p.
Clay is a major industrial mineral resource in Arkansas. Combined industry output in 2005 amounted to over 1.2 million tons of raw clay, valued at over $1.9 million. In 2005, Arkansas ranked 6th in the nation in production of common clays. Few data concerning tonnage and grade of individual clay deposits in Arkansas are available, but the amount of potentially useful clay in Arkansas is substantial.
Over the past two decades, the brick industry of Arkansas has consolidated to one major producer, Acme Brick of Perla in Hot Spring County. Sandy kaolinitic clays of the Wilcox Formation (Eocene) are the source of the bulk of common clay in Arkansas. Wilcox clays, alone or mixed with clay from other geologic units, are usable for most ceramic products, especially refractory brick and heavy clay products. Deposits in the Wilcox Group in Hot Spring, Ouachita, and Hempstead Counties have been particularly important. Some building brick has also been manufactured from surface clays and shales in other regions of the state.
Beginning in the early 1950’s, bloating clay was expanded for lightweight aggregate at Poyen, Grant County. Alluvial clay suitable for lightweight aggregate has been mined near England, Lonoke County, and was recently being mined in Crittenden County. Most of the physiographic provinces of the state contain major resources of this material. In the Ozark region, black fissile shales of the Atoka Formation (Pennsylvanian) constitute a major potential resource. In the Arkansas Valley, clays derived by the weathering of shales in the Hartshorne Sandstone are potentially useful. The bloating-clay resources of the West Gulf Coastal Plain include tuffaceous sediments of the Woodbine Formation (Cretaceous), Brownstown Marl (Cretaceous) and some clays of the Wilcox Group (Eocene). Smectite clays in Arkansas have received some attention for use as commercial grade "kitty litter". Such clays are common in the Midway Group (Tertiary) in central Arkansas and in several Cretaceous formations in southwestern Arkansas. High bloating characteristics with a medium firing range result in a frothy porosity which is ideal for a high-absorbency product. The Mississippi River Alluvial Plain contains major resources, including surficial alluvial (recent stream) deposits and the loess (wind-blown dust) deposits of Crowley's Ridge. Few detailed studies of reserves of individual deposits have been done, but Arkansas' potential reserves of clay (and shale) that qualify for bloating appear large.
Clays having the properties necessary for pottery and stoneware use are present in the Ouachita Mountain and Arkansas Valley regions and were formed by the weathering of shales in the Atoka Formation and Stanley Shale (Pennsylvanian and Mississippian, respectively). Most Cretaceous clays in southwest Arkansas are calcareous and are not suitable for ceramic purposes. Ceramic and pottery clays occur in southeastern Arkansas, primarily in the Midway Group (Paleocene), and the Wilcox and Jackson Groups (both Eocene) and in Quaternary sediments.
In the Gulf Coastal Plain region, fire clays have been mined from kaolin deposits in the Tokio Formation (Cretaceous) in Pike County. Some fire clays (as underclays), associated with lignite, are locally present in the Wilcox Group. Some Wilcox clays in Ouachita and Hot Spring Counties are suitable for manufacturing fire brick. High-alumina clays, associated with bauxite deposits in Pulaski and Saline Counties in central Arkansas, are potential sources for refractory materials.
Changes have occurred in the various clay industries in recent years. Some changes are due to technological advances, changing economic conditions, opening new markets, shifts in demand, and increases in both domestic and export markets. Changing conditions which affect the clay industry in Arkansas include increasing freight rates, energy costs, production and marketing costs, and governmental control (mining laws). An example of this changing situation is the public’s attitude towards landfills. At one time, rubbish disposal did not require containment of the liquid products of any landfill, but it does today. Clay liners are commonly installed during landfill construction. The types of clay used vary according to the type of material the landfill will contain. Untreated clays used industrially as clay liners include kaolinite, smectite, and palygorskite. Each clay has very different physical and chemical properties, allowing their use as liners in differing situations.
The principal clay mineral composing bentonite is smectite. Smectite is most often used as a group name, encompassing a number of very fine grained minerals which possess certain ion-exchange characteristics. Bentonite's commercial value is due to its ion-exchange ability, which determines the clay's physical expansion and colloidal properties. Sodium-rich bentonites are valuable for well-drilling muds which must flow when shaken or stirred, but harden when left undisturbed (thixotropy).
Bentonite occurs as bedded deposits and as a hydrothermal mineral. Bentonite beds that originated as an alteration of waterlaid volcanic ash, deposited in either fresh or saline water, are commercially the most important source of this resource. In the Gulf Coastal Plain of Arkansas, beds of bentonite are present in the Midway Group (Paleocene). Several of these bentonitic beds contain fuller's earth. Bentonite has not been mined in Arkansas, although small deposits of certain clays that have the desired bentonitic properties after treatment have been mined.
Bloating clay may be defined as any fine-grained clayey material which, upon firing, expands or bloats into a frothy mass with closed cellular texture within a limited temperature range. In practice, the definition can be extended to include some shales, slates, and mine wastes. After being ground to fine size and mixed with water, some of these particles are clayey and can be used as feedstock for making lightweight aggregate. The property of expansion upon firing is desired because bloated material, when used as an aggregate in concrete, reduces the weight of the final product. Two conditions are necessary to bring about bloating. During firing, when the bloating temperature is reached, the general clayey mass must be in a plastic condition and, simultaneously, gases must be evolving throughout the mass. Plasticity is developed by the fluxes that start a fusion and, in this state, the gases can not readily escape. The result is a mass of thin-walled cells, resembling pumice in appearance. After firing, the expanded clay is ground or broken to various sizes and is used in concrete structures, lightweight building block, and precast or prestressed concrete structural members. The use of lightweight aggregates results in considerable monetary savings in structural steel and foundation design on new and existing structures, and in some applications, strength is greater than it would be if heavier rock aggregate were used. Other applications include loose insulation, plaster and stucco aggregate, mulching agents for horticultural applications, bases for sports tracks, and refractory (high temperature) materials.
Briefly, beginning in the early 1950’s, clay was expanded for lightweight aggregate at Poyen, Grant County. Alluvial clay suitable for lightweight aggregate has been mined near England, Lonoke County, and is currently being mined in Crittenden County. Most of the physiographic provinces of the state contain major resources of this material. In the Ozark region, black fissile shales of the Atoka Formation (Pennsylvanian) constitute a major potential resource. In the Arkansas Valley, clays derived by the weathering of shales in the Hartshorne Sandstone are potentially useful. The bloating-clay resources of the West Gulf Coastal Plain include tuffaceous sediments of the Woodbine Formation (Cretaceous), Brownstown Marl (Cretaceous) and some clays of the Wilcox Group (Eocene). Smectite clays in Arkansas have received some attention for use as commercial grade "kitty litter". Such clays are common in the Midway Group (Tertiary) in central Arkansas and in several Cretaceous formations in southwestern Arkansas. High bloating characteristics with a medium firing range result in a frothy porosity which is ideal for a high-absorbency product. The Mississippi River Alluvial Plain contains major resources, including surficial alluvial (recent stream) deposits and the loess (wind-blown dust) deposits of Crowley's Ridge. Few detailed studies of reserves of individual deposits have been done, but Arkansas' potential reserves of clay (and shale) that qualify for bloating appear large. A potential source of lightweight aggregate in Arkansas is tripoli (see Tripoli).
Clay suitable for the manufacture of heavy clay products, such as building and paving bricks, drain tile, and sewer tile, are present in several areas of the state and have been utilized for many years. Many deposits of kaolin, ball clay, and fire clay are suitable for heavy clay products. To manufacture heavy clay products, the natural material must possess certain working and drying properties, the most important include plasticity when wet, little shrinkage when drying and being fired, and good strength as both a green (unfired) and fired product. The fired color of the clay is important to both the consumer and manufacturer. A building-brick clay that fires white may be developed commercially because, by the addition of various minerals, the color may be modified to meet whatever is popular among consumers. Clay from another deposit, otherwise comparable in size and clay quality, that fires to a red to orange color may not be commercially suitable for the brick industry, but may be considered usable by the manufacturer of unglazed clay flower pots.
Geologically and volumetrically, the most important source of clay in Arkansas is the Wilcox Group (Eocene). Wilcox clays, alone or mixed with clay from other geologic units, are usable for most ceramic products, especially refractory brick and heavy clay products. Deposits in the Wilcox Group in Hot Spring, Ouachita, and Hempstead Counties have been particularly important. Some building brick has also been manufactured from surface clays and shales in other regions of the state.
Fuller's earth, or natural bleaching clay, is any natural or treated clay which, when used as a filter, effectively removes color and clarifies various mineral and organic oils. Mineralogically, fuller's earth is predominantly smectite (calcium montmorillonite), but typically includes some kaolinite and attapulgite. The importance of fuller’s earth to industry is due to its bleaching properties. Deposits of fuller's earth were mined by underground methods near Olsen Switch, 7 miles south of Benton in Saline County, between 1901 and 1922. The deposits were formed by the weathering of igneous dikes of Cretaceous age. The original igneous rock was altered to a depth of 200 feet, probably in early Tertiary time, while bauxite was forming nearby. Several deposits of bentonite, which upon treatment with weak acid have good bleaching or clarifying properties, are reported in Pulaski and Saline Counties. These bedded deposits are in the Midway and Wilcox Groups (Paleocene and Eocene, respectively)
Kaolin has numerous industrial applications and new uses continue to be discovered. It is a unique industrial mineral due to several properties, including chemical inertness over a wide range of acid-alkaline conditions, white color, good covering or hiding power when used as a pigment or extender in coated films and in paper-filling applications, softness and non-abrasive properties, low conductivity of heat and electricity, and lower cost than most competitive materials. Some uses of kaolin require very rigid specifications including particle-size distribution, color and brightness, and viscosity. Other applications require none of these, an example being the use of kaolin in the manufacture of cement. Nationally, the higher grades of kaolin compose the bulk of the tonnage sold and have the highest unit value. Many grades are designed for specific uses, particularly for the paper, paint, rubber, plastics, and ceramics industries. Deposits of high-purity kaolin have been and will continue to be sought in Arkansas. Currently, no deposits have been discovered that are suitable to the paper industry, but continuing research into the uses and applications of kaolin may result in expanded use.
Clays used for pottery and stoneware are principally kaolin and/or ball clay. To be successfully worked and dried, the clay must be plastic when wet, shrink little while drying, and resist warping and breaking after being dried before firing. At this stage, it is known as "greenware". After firing, the final product must be hard, strong, nonporous and of suitable color. Household items manufactured using pottery clays include porcelain sinks and waterclosets (toilets), some chinaware, various types of ovenproof cookware, stoneware and other kitchen and dinnerware, ceramic floor and wall tile, and decorative items. Pottery has been manufactured from red-orange residual clays in the Ozark Plateaus region of Arkansas. Clays having the properties necessary for pottery and stoneware use are present in the Ouachita Mountain and Arkansas Valley regions and were formed by the weathering of shales in the Atoka Formation and Stanley Shale (Pennsylvanian and Mississippian, respectively). Most Cretaceous clays in southwest Arkansas are calcareous and are not suitable for ceramic purposes. Ceramic and pottery clays occur in southeastern Arkansas, primarily in the Midway Group (Paleocene), and the Wilcox and Jackson Groups (both Eocene) and in Quaternary sediments.
Refractory clays exhibit a range of high melting temperatures which make them useful wherever high-temperature applications exist. Refractory bricks line the roasting and processing furnaces of various high-temperature processing plants and ceramic kilns, and compose crucibles, condensers, and many types of laboratory glassware. The white ceramic insulator portion of gasoline engine spark plugs are manufactured from refractory clay and coated with vitrified kyanite (Al2SiO5). In addition to the high melting temperatures, refractory clays must have good greenware strength and exhibit minimum shrinkage and warpage. Kaolinite, flint clay, plastic fire clay, ball clay, and various calcined materials, such as bauxite, qualify as refractory resources. The product is generally hard and may vary in porosity. In the Ozark region of Arkansas, some shales in the Atoka Formation (Pennsylvanian) have the firing properties necessary to manufacture refractory materials such as fire brick. Clays generated from weathered Pennsylvanian strata in the Arkansas Valley constitute abundant fire-clay resources. These clays are often underclays associated with coal beds. Although the shale units of the Ouachita Mountain region are highly varied, fire clay resources are present. In the Gulf Coastal Plain region, fire clays have been mined from kaolin deposits in the Tokio Formation (Cretaceous) in Pike County. Some fire clays (as underclays), associated with lignite, are locally present in the Wilcox Group. Some Wilcox clays in Ouachita and Hot Spring Counties are suitable for manufacturing fire brick. High-alumina clays, associated with bauxite deposits in Pulaski and Saline Counties in central Arkansas, are potential sources for refractory materials.
Arkansas clay resource
Clay is a major industrial mineral resource in Arkansas. Combined industry output in 1995 amounted to over 1 million tons of raw clay, valued at over $1.2 million. In 1995, Arkansas ranked 4th in the nation in production of both kaolin and fire clays, and 9th in common clays. Few data concerning tonnage and grade of individual clay deposits in Arkansas are available, but the amount of potentially useful clay in Arkansas is substantial. Changes have ocurred in the various clay industries in recent years. Some changes are due to technological advances, changing economic conditions, opening new markets, shifts in demand, and increases in both domestic and export markets. Changing conditions which affect the clay industry in Arkansas include increasing freight rates, energy costs, production and marketing costs, and governmental control (mining laws). An example of this changing situation is the public’s attitude towards landfills. At one time, rubbish disposal did not require containment of the liquid products of any landfill, but it does today. Clay liners are commonly installed during landfill construction. The types of clay used vary according to the type of material the landfill will contain. Untreated clays used industrially as clay liners include kaolinite, smectite, and palygorskite. Each clay has very different physical and chemical properties, allowing their use as liners in differing situations.
Branner, J. C., 1908, The clays of Arkansas: U. S. Geological Survey Bulletin 351, 247 p.
Miser, H. D., 1913, Developed deposits of fuller's earth in Arkansas: U. S. Geological Survey Bulletin 530, p. 207-220.
Williams, N. F., and Plummer, Norman, 1951, Clay resources of the Wilcox group in Arkansas: Arkansas Resource and Development Commission, Division of Geology, 98 p.
Diamond is the hardest known substance, being composed of very densely packed carbon (C). Diamond has unique physical and chemical properties, aside from its brilliance and "fire" when properly faceted into a gemstone, which make it one of the most important minerals to industrialized society. Due to superior hardness, industrial grade diamond powders are often used to cut and polish all types of gem-grade stones. Along with its abrasives applications, other uses include heat sinks in electronic components, infrared windows in heat detectors, surgical blades, glass cutting and engraving tools, wire drawing dies, metal cutting tools, and drill bits. When tungsten carbide cutting tools were introduced during World War I, industrial diamond use increased greatly, principally for grinding and sharpening these tools. During World War II, demand for all industrial applications of diamond again increased dramatically. In 1955, General Electric Company announced the development of an industrial process for the manufacture of synthetic diamond. This was followed by a similar announcement in 1959 by De Beers Consolidated Mines Ltd. Today, the production of industrial grade synthetic diamond (336 million carats or 148,151 pounds) greatly overhadows the world's output of natural diamond. In 1989, natural industrial diamond accounted for 55 percent of the world's diamond production. Since diamonds were discovered over 2,000 years ago, only about 380 tons of natural (industrial and gemstones, combined) diamond have been recovered.
Evidence from conditions required to grow artificial diamonds and studies of minerals included in natural diamonds indicate that diamond is only formed at depths greater than 120 miles below the earth's surface and at temperatures greater than 2,000o F. Under these conditions, diamond is the stable form of carbon and was apparently captured and swept upward by igneous intrusions. These igneous rocks are called lamproites and kimberlites.
Arkansas Diamond-bearing Rocks
One of the few places in North America where diamonds are present in their host rock and the only place tourists may hunt for diamonds is the Prairie Creek pipe in Arkansas. It is roughly triangular in surface outcrop, exposed over 73 acres, and is situated 2.5 miles southeast of Murfreesboro in Pike County. The site has been known to geologists since 1842. It is a breccia-filled volcanic pipe of Cretaceous age, formed by a series of gaseous explosions as are several other pipes nearby.
Various rock types are present in the Arkansas diamondiferous pipes. Magmatic lamproite is a dark-colored igneous rock with a texture that has two distinct grain sizes (porphyritic). Some of it was broken explosively as it neared the earth's surface. This broken rock material is lamproite breccia tuff. Rarely have diamonds been reported in the soils formed by the weathering of magmatic lamproite; most have been recovered in the lamproite breccia tuff or in the thin residual soils overlying this rock. Microdiamonds, however, have been recovered from the magmatic rock by special techniques. Epiclastic rock, which is a rock formed by the mechanical mixing of tuffaceous volcanic material and local Cretaceous sediments, was recently recognized by geologists.
History of Arkansas Deposits
Diamonds were first discovered in Arkansas in 1906 when two stones were picked up by John M. Huddleston near the mouth of Prairie Creek southeast of Murfreesboro. Following this discovery, diamonds were reported from two small areas 2 miles to the northeast of the Prairie Creek pipe. Later, various efforts were made to mine diamonds on a commercial basis, but without sustained success. In 1919, the Arkansas Diamond Corporation was organized and a washing plant was built which processed 18,000 loads of surface-mined diamond-bearing material in 1920. The corporation discontinued operations after 9 months. Early in 1940, the property was taken over by The Diamond Corporation of Arkansas. Their 2,000-ton washing and concentrating plant began operation in 1948, but shut down a year later. Howard A. Millar operated the "Crater of Diamonds" tourist attraction on part of the Prairie Creek pipe during the 1950’s and 1960’s. This volcanic pipe and some surrounding acreage became Crater of Diamonds State Park in 1972 when the State of Arkansas purchased the property for $750,000 from General Earth Minerals. From 1972 to 2006 inclusive, over 2 million guests had visited the Park.
Recovery figures are incomplete, but estimates are that about 125,000 diamonds, thought to average 0.25 carats in weight, have been recovered by commercial efforts and by tourists. Since the Prairie Creek pipe became a state park in 1972, the state has maintained records of the number of diamonds discovered and reported. From 1972 to 2006 inclusive, over 25,000 diamonds weighing a total of over 4,500 carats have been reported (Crater of Diamonds, Diamonds Statistics Summary). It is not known what percentage of the stones from Arkansas are of industrial grade.
In the early 1990’s, drill-hole data on the Prairie Creek pipe indicated about 78 million tons of diamond-bearing rock are present to a depth of 650 feet. Several nearby diamond-bearing lamproite pipes are present northeast and east of the state park on private property. For information concerning gem-quality diamonds, see the Diamond article under Gemstones.
Howard, J. M., 1989, Finding diamonds in Arkansas!, Arkansas Geological Commission pamphlet.
Krol, L. G., 1988, Prairie Creek kimberlite (lamproite), in Colton, G. W., ed., Proceedings of the 22nd Forum on the Geology of Industrial Minerals: Arkansas Geological Commission Miscellaneous Publication 21, p. 73-75.
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.
Miser, H. D., and Ross, C. S., 1922, Diamond-bearing peridotite in Pike County, Arkansas, in Contributions to economic geology, pt. 1: U. S. Geological Survey Bulletin 735, p. 279-322.