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Industrial Minerals AKA Non-metallic Minerals E - NAs defined here, a gem is any jewel, whether stone or pearl, having value and beauty that are intrinsic. A gemstone or gem material is a stone or material from which a gem may be cut. Gems are used for personal adornment, display, or in manufactured objects of art because they possess beauty, rarity, and durability. Arkansas has within its borders several stones or materials which, by popular definition, are considered gemstones. They are: amber, diamond, onyx , pearls, (fresh water), quartz (several varieties), and turquoise. In 1995, Arkansas ranked 3rd in the nation in value of gemstones produced ($4.89 million). Amber Amber is brittle, yellowish to brownish, translucent to transparent, fossilized tree resin. It may enclose insects and other organisms. Gem-quality amber takes a high polish. Gem-grade amber is often used to make faceted beads and irregular shaped polished drops. Larger pieces may also be manufactured into mouth pieces for pipes or cigarette holders, although less expensive plastics now substitute almost entirely for this market. Diamond The 1967 Arkansas General Assembly passed legislation which became Act 128 designating diamond as the official gem of the State. A number of diamonds recovered from the volcanic pipes near Murfreesboro qualify as gem-grade material. The largest diamond discovered in the United States came from this site and was recovered by commercial methods. Named the "Uncle Sam", this diamond was discovered in 1924. It weighed 40.23 carats in the rough, and was faceted into an elongate emerald-cut gemstone weighing 12.42 carats. It has a faint rose color and is presently owned by Peiken of Fifth Avenue, New York.
The best known diamond recovered by a tourist is the "Star of Arkansas", a white 15.33-carat crystal which was faceted to a flawless 8.27-carat marquise-shaped gem. This stone was auctioned at Christie's of New York in 1994 and brought $145,000. The largest diamond discovered since the beginning of Crater of Diamonds State Park in 1972 is the "Amarillo Starlight", weighing 16.37 carats. This stone was faceted to a 7.54-carat marquise-shaped gem, valued at between $150,000 and $175,000. Records of diamonds discovered at Crater of Diamonds State Park for the period of 1972 to 2007, inclusive, indicate that 734 diamonds were reported that weighed over 1 carat each (Crater of Diamonds State Park, Diamonds Statistics Summary). Some of these stones would qualify as cuttable gemstones. Onyx is a variety of banded calcite (CaCO3) deposited by water in caves. Inexpensive carved figurines, table tops, and interior decorative items are the stone's principal uses. There are numerous caves in northern Arkansas. Currently, it is illegal to remove or disturb cave formations in the state. Arkansas has no recorded history of use of this resource. Pearls A pearl consists of concentric layers of the mineral aragonite (CaCO3) formed as nacre secreted by a mollusk to cover an internal irritant. Pearls are recovered from fresh- and salt-water bivalve shellfish. In Arkansas, fresh-water mussels of the genus Unios are the principal source of pearls. A pearl's value depends on its weight, luster, perfection of shape (sphericity), color, translucency, and stability in air. The luster and translucency are controlled primarily by the thickness of the nacre. It is difficult to grade the value of any given pearl without considerable experience. Quartz Varieties Gemstone varieties of quartz (SiO2) present in Arkansas include the cryptocrystalline varieties (agate, jasper, chalcedony, banded chert) and crystalline varieties (rock crystal, amethyst, smoky quartz). Another material potentially usable by lapidaries is silicified petrified wood. Opal, a non-crystalline form of silica is discussed in this section also.
Rock Crystal
Turquoise The mineral turquoise (Cu2+Al6(PO4)4(OH)8 . 4H2O) is the end member of a mineral series in which copper is substituted for iron; chalcosiderite is the other end member. Intermediate in composition in the series between these two minerals are the minerals planerite and rashleighite. However, to the lapidary, any and all of these minerals are considered turquoise if the material will cut and polish. Hand-crafted turquoise and silver jewelry has become increasingly popular with the general public. In Arkansas, turquoise group minerals are present in the Ouachita Mountains, usually associated with the secondary mineralization present in lead-, zinc-, and copper-bearing quartz vein deposits as thin fracture-filling seams in the sandstone or shale host rock. In some places turquoise is present as hard, translucent bluish films where no primary copper mineralization is evident. In these instances, the host rock is almost always the Arkansas Novaculite (Devonian-Mississippian) or the Bigfork Chert (Ordovician). Planerite is often associated with either secondary aluminum phosphates or manganese mineralization. Three localities of "turquoise" mineralization are notable in Arkansas. In 1974, a turquoise prospect on Porter Mountain in Polk County was tested by a company based in Denver, Colorado. The company reported that about 200 pounds of fair to good gem-quality turquoise had been processed from this location, of which about 10 pounds were sold for $100 per pound. The host rock is tripolitic novaculite. The site, named the Mona Lisa mine, was intermittently mined by open-pit methods, with a reported total recovery of over 1,000 pounds, until the late 1980’s. Much of the output of the Mona Lisa mine was dyed, stabilized, and compressed into cylinders for shipment to China as carving stock. Some treated and untreated gem material was marketed in New Mexico and Arizona. Final reclamation took place on this site between 1989 and 1991. Another locality in Polk County is the Coon Creek manganese mine. Planerite is moderately abundant as thin green films coating novaculite boulders and cobbles. However, no gem- or cutting-grade material is located at this site. Planerite was also abundant at the Montgomery County quarry on Mauldin Mountain, Montgomery County. Planerite formed as thin coatings and crusts on Bigfork Chert, often in association with wavellite, an aluminum phosphate. No gem material is located at this site.
Greensand is the name commonly applied to a sandy rock or sediment containing a high percentage of the mineral glauconite. Glauconite ((K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10 (OH)2) is a greenish-black to blue-green mineral which forms in shallow marine sedimentary deposits. Because of its potash and phosphate content, greensand has been marketed for over 100 years as a natural fertilizer and soil conditioner. Greensand is recommended by organic gardeners as a mulch, top dressing, and soil- conditioning additive for both potted plants and vegetable gardens. The slow release rate of plant nutriments (potash and phosphate) minimizes the possibility of plant damage by fertilizer "burn" while the mineral's moisture retention aids soil conditioning. Early in the 1900’s, glauconite was recognized as having chemical exchange properties in water solutions, which led to its use as a water softener. In southwest Arkansas, greensands are abundant in the Cretaceous Nacatoch and Ozan Formations. Greensands in the Nacatoch Formation are more extensive, contain higher percentages of glauconite, and are richer in potash (2.8-4.5 percent) than the Ozan Formation. These formations extend from the Oklahoma-Arkansas state line near Foreman in Little River County northeastward to Arkadelphia in Clark County and dip gently to the south-southeast. Greensands of the Nacatoch are exposed intermittently from Columbus, Hempstead County, to Terre Noire Creek in Clark County. Notable exposures are present near Washington, Hempstead County, and along the banks of a branch of Moore's Creek in Clark County. Outcrops of the Ozan Formation are scattered, extending from western Little River County near Foreman to north-central Hempstead County. The glauconite is present in a sandy micaceous marl near the base of the formation. This basal sand can be 3 to 15 feet thick and contain up to 50 percent glauconite. Markets for greensand consist of small- to medium-sized water treatment companies providing domestic and small water-system services and designers and manufacturers of medium to large water-treatment systems who service their installed facilities. Also, potential exists to market Arkansas greensand at organic garden supply stores as a bagged commodity. Presently, in the United States, economical greensand deposits contain at least 90 percent glauconite. The deposits must not contain more than 2 to 3 percent clay matrix and must show no evidence of weathering. There has been no mining of greensands in the state. Ashley, G. H., 1917, Notes on the greensand deposits of the United States: U. S. Geological Survey Bulletin 660, p. 27-49. Gypsum deposits are mined by open-pit methods in southwest Arkansas from the DeQueen Limestone (Early Cretaceous) of the Trinity Group. The formation is exposed in a narrow belt extending from the Little Missouri River in Pike County westward through Howard and Sevier Counties, and dips gently to the south. The greatest thickness of a single gypsum bed (12 feet) is at Plaster Bluff in Pike County. In a major operation near Briar, Howard County, 5 beds of massive gypsum with an aggregate thickness of as much as 20 feet are mined. Satin spar is interbedded with clay units as thin layers (0.5 to 2.5 inches in thickness), both above and below the 5 minable layers of alabaster. The first recorded mining of gypsum in Arkansas was in 1922. Continuous gypsum production started in 1936. By 1961, yearly production had risen to 166,698 tons. In 1963, Dierks Forest, Inc. opened the Briar Gypsum plant in Howard County. This mining and manufacturing facility was one of the 10 largest producers of wallboard in the world. The property has changed hands several times over the past 40 years; owner/operators have included Weyerhaeuser Company, James Hardy Gypsum, Boral, and BPB Gypsum. In 1993 at this site, 1,175,000 cubic yards of overburden were removed and 630,000 tons of gypsum were mined. From this, 660 million square feet of wallboard was produced. In late 1997 under James Hardy Gypsum, a major expansion of the facility doubled the plant’s wallboard manufacturing capability, which now has a capacity of 1.4 billion board feet annually, the world’s largest wall board production plant. The mining property and plant are now owned by Certain Teed Company. A local company, Highland Gypsum Company, operated a small mine near the community of Highland in Pike County. The mine’s output was used locally as a cement additive. The Highland mine was purchased by C. W. Harrison of Oklahoma and is now closed and reclaimed. Even with a 50% increase in gypsum production, the State remained 6th in rank nationally in 2005. Dane, C. H., 1929, Upper Cretaceous formations of southwestern Arkansas: Arkansas Geological Survey Bulletin 1, 215 p. The principal mineral of limestone is calcite (CaCO3), a form of calcium carbonate. Dolostone is quite similar to limestone, but is composed mostly of the mineral dolomite (CaMg(CO3)2). Both are sedimentary rocks that occur as thin to massive beds of fine- to coarse-grained rock. Their color is typically some shade of gray, but may be white, tan, yellow, pink, purple, reddish brown, brown, or black. Limestone readily reacts with hydrochloric acid and produces carbon dioxide (CO2) as a gas. By contrast, dolostone is less reactive and normally must be in powdered form to react visibly. Pure dolomite contains 54.28 percent calcium carbonate and 45.72 percent magnesium carbonate. Dolostone is commonly referred to by its mineral name, dolomite. Limestone is composed of material derived by both chemical and biological activities. The particles of sediment that make up a typical limestone are frequently recognizable as fossil fragments. By contrast, most dolostone is crystalline. Dolostone forms when magnesium in pore water is substituted for some of the calcium in the original limestone, or by direct precipitation. Most limestones of commercial importance accumulated in relatively shallow marine environments and are widely available for utilization. Carbonate rocks form about 15 percent of the earth's sedimentary strata. 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. A Tertiary-age limestone in the Midway Group is present in the Gulf Coastal Plain between Little Rock in Pulaski County and Benton in Saline County. 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 uses are in the manufacture of quicklime (CaO) and other chemical feedstock items, crushed stone, riprap, building and dimension stone, cement, and agricultural limestone. The most important use of dolostone for which limestone cannot be substituted is in the manufacture of refractory dolomite and in the preparation of heat-insulating materials. Limestones and dolostones high in silica are suitable for the manufacture of mineral or rock wool for insulation. Some high-purity limestones in northern Arkansas have been used as source material for calcium-based food supplements. Crushed limestone, used largely as concrete and asphalt aggregate, is the major product of limestone 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, concrete aggregate, and as agricultural limestone. Some limestone- and dolostone-bearing formations are quarried for building or ornamental stone, mostly in Independence County. Currently, one company produces quicklime (CaO) from its facility near Batesville in Independence County. The raw rock is hand sorted and transported a short distance from the quarry to the kilns by a narrow gauge railway. Limestone and dolostone are quarried from open pits and underground mines. Drilling and blasting releases the stone from the outcrop and provides first-order breakage. The rubble is then hauled to a crushing facility where the stone is further crushed, screen-sorted into size classes, and stored. Limestone needed for high-purity applications (quicklime and food supplements) is usually hand-sorted at the mine. In the manufacture of quicklime, limestone is crushed to lump size (usually 5-8 inches) and heated in a kiln to temperatures of around 2,000o F. The process is called calcination and works by driving off carbon dioxide from the calcite, forming calcium oxide (quicklime). Limestone used as a source of nutritional calcium is simply ground into a powder, mixed with other supplements and binders, and reformed into pills or capsules. Stone that is to be used for its ornamental qualities is extracted from the bedrock by saws and wedges. Afterwards, the rock is either cut or carved to its final shape. Polishing may be used to finish the product. No records of annual production of limestone and dolostone are readily available from Arkansas because they are grouped with other types of rock aggregate production, but yearly production tonnage is significant. Branner, G. C., 1941, Limestones of northern Arkansas: Arkansas Geological Survey, 24 p. Commercial marbles mined in Arkansas are all unmetamorphosed limestones or dolostones that take a high polish. Marble is used primarily as a building and ornamental stone, in monuments, table tops, wash basins, statuary, and other decorative applications. Several types and grades of commercial marble have been mined from quarries in Arkansas. The crystalline texture of Arkansas marbles varies from coarse to fine and colors range from light gray to black, tan to yellow to rust, and they may have one uniform color or several shades. Often, primary sedimentary structures or structures produced by the actions of organisms (or both) add uniqueness and interest to the stone, making it more marketable. Marble is mined exclusively from limestones and dolostones of Paleozoic age in north Arkansas. Principal "marble"-producing formations include the Plattin, Kimmswick, and Fernvale of Ordovician age, the St. Clair of Silurian age, and the St. Joe, Boone, and Pitkin of Mississippian age. Other stratigraphic units are sometimes quarried for stone when exploration reveals a unique quality that is in demand. The largest producer of polished and cut marble products in Arkansas is Oran McBride Stone Company of Batesville in Independence County. The company produces both polished and other finished interior and exterior products from several quarry operations, depending upon what is popular in the marketplace. Broken dimension stone (Cotter formation) of various tones is produced by Johnson Landscaping from their quarry north of Eureka Springs in Carroll County. Eureka Stone Co., the saw shop, is located near the quarry, and produces a variety of sawn and turned architectural pieces. The first export of marble from Arkansas was in 1836, the year Arkansas became a state. A large block of Early Mississippian limestone was quarried near Marble Falls in Newton County and sent to Washington, D.C., to be used in the construction of the Washington Monument. Marble production has been intermittent throughout most of its commercial history, but in recent years the use of products made of Arkansas marble has steadily increased. Most current mining operations of commercial marble in Arkansas are located near Batesville, Independence County. Hopkins, T. C., 1893, Marbles and limestones: Arkansas Geological Survey Annual Report for 1890, v. IV, 443 p. Marl is a sediment or sedimentary rock that is a mixture of clay and calcite (CaCO3). Arkansas marls may also contain glauconite, sand, and marine shell deposits. Marl is used in the manufacture of cement and for agricultural purposes. Commercially, the most important marl-bearing formation in Arkansas is the Marlbrook Marl, a dark blue-gray, fossiliferous, chalky sedimentary unit of Cretaceous age. It may contain minor sand, glauconite, or phosphate grains. The Marlbrook Marl, which can be 220 feet in thickness, dips gently to the south-southeast at about 80 feet per mile. Exposures are present from near Arkadelphia, Clark County, southwestward to Foreman in Little River County. Particularly notable exposures of the Marlbrook Marl are present in and near Ozan Creek south of the community of Ozan along Arkansas Highway 4 in Hempstead County. The Ozan Formation, another marl-bearing unit, and the Brownstown Formation are sandy marls containing glauconite, some phosphate nodules, and invertebrate shells. The Arkadelphia Marl is chiefly marl and marly clay containing sandy clay and limestone, and impure chalk. All of these Cretaceous formations dip gently to the south-southeast and crop out along the same trend. In Arkansas, the Marlbrook Marl is currently used as a source of silica in the manufacture of cement. Ash Grove Cement Company mines marl near the community of Foreman, Little River County. Branner, J. C.,1898, The cement materials of southwest Arkansas: American Institute of Mining Engineers Transactions, v. 27, p. 53. Nepheline syenite is a medium to coarse-grained, light- to medium-gray, igneous rock that is composed predominantly of a silicate mineral called orthoclase (KAlSi3O8) and has a granite-like appearance. It may be distinguished from granite by little or no quartz content (free SiO2). In Arkansas, nepheline syenite has been intruded into the sequence of Paleozoic sedimentary rocks. Locally, quarrymen recognize "blue granite" and "gray granite" varieties. 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. 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 quarry is actively producing nepheline syenite near Bryant in Saline County. Mining of nepheline syenite exceeds 5 million short tons annually. Gordon, Mackenzie, Jr., Tracey, J. I., and Ellis, M. W., 1958, Geology of the Arkansas bauxite region: U. S. Geological Survey Professional Paper 299, 268 p. Novaculite is a sedimentary rock composed mostly of microcrystalline (1-5 micron) quartz and is a crystallized variety of chert. It is dense, hard, white to grayish-black in color, translucent on thin edges, and has a dull to waxy luster. It typically breaks with a smooth conchoidal (shell-like) fracture. The word novaculite is derived from the Latin word novacula, meaning razor stone. Whetstone grade novaculite has a distinct triple point texture, developed by pressure metamorphism during the formation of the Ouachita Mountains. Griswold, L. S., 1892, Whetstones and the novaculites of Arkansas: Arkansas Geological Survey Annual Report for 1890, v. III, 443 p. |
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