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Gemstone

As 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.
Amber has a low specific gravity (1.0-1.1) and is soft (2-2.5 on Mohs scale).    Amber burns with a strong "tar" odor due to its hydrocarbon composition.  Amber is also soluble in some petroleum-based solvents, such as acetone.

Worldwide, amber is recovered from alluvial soils, clays, recent sediments, beds of lignite, and along some seashores where offshore deposits are disturbed during storm activity, as the Baltic Sea.  In Arkansas, amber is associated with lignite beds of Tertiary age uncovered during the mining of brick clay south and east of Malvern in Hot Spring County. Although no gem-grade amber has been reported in these deposits, paleontologists have discovered several new species of insects in Arkansas amber.


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.

new diamond.jpg (13385 bytes)

17 carat Arkansas diamond crystal from Pike County from the Roebling collection in the US National Museum (Smithsonian).
           Photo by Chip Clark.


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.

A particularly notable recently discovered diamond that was cut and found to be a flawless perfect top quality colorless stone is the Stawn-Wagner diamond. It weighed 3.03 carats rough and was cut to a brilliant round gem of 1.09 carats. Gemologists have graded the stone as grade D-flawless, 0/0/0 (cut, color, clarity) and stated that this diamond is one in a billion! It was purchased by the Crater of Diamonds State Park for $34,500 in 1999, using part grant money and part private donations. This flawless gem may be viewed at the Park.

Active mining operations ceased with the destruction of the first mills by fire in the early 1920s. No commercial operation has existed since that time although several major and a number of minor diamond exploration companies have investigated both the Prairie Creek and several adjacent smaller pipes, particularly in the 1980s and early 1990s. The Prairie Creek, being a state park, is now by law excluded from further commercial examination.


Onyx

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.

Although pearls were occasionally collected by Arkansas' fishermen, little notice was taken until 1895, when a survey party recovered pearls from fresh-water mussels in the White River. When this collection of pearls sold for $5,000, many people began to search for the gems in the White, St. Francis, and Arkansas Rivers and their tributaries. Within a year, nearly every major stream in Arkansas had yielded pearls. The highest quality and most extensive collections came from the White and Black Rivers in north-central and northeast Arkansas. The pearling industry was centered at Black Rock, Independence County, where, at one time, more than 1,000 people were gathering pearls within 20 miles of the town. The Black River proved to be the nation's richest pearling region. During the early years of pearling excitement in Arkansas, a large percentage of the choice pearls were discovered loose, lying in mud along cutoff meander lakes and river backwater shorelines. At the height of the excitement in 1897, many people purchased unopened mussels, speculating on the discovery of valuable gems. Between l895 and 1898, over $500,000 worth of pearls were recovered by Arkansas' pearling industry.

Individual Arkansas pearls have sold for up to $25,000, but pearls valued up to a few hundred dollars are considered exceptional. The $25,000 pearl was round, weighed 103 grains (almost one-quarter ounce), and was discovered in the Black River in 1904. A necklace displayed at the St. Louis World's Fair in 1904 was composed of 16 Arkansas pearls which had a combined weight of 861 5/8ths grains (nearly 2 ounces). A pearl found at Newport, Arkansas, is set in one of the Royal Crowns of England. Usually fresh-water pearls do not compare with salt-water pearls, but the exceptional luster and color of some fresh-water pearls do command high prices.

Presently, Arkansas has one commercial pearl business, Pearls Unique of Newport, Jackson County. Arkansas continues to be second in commercial freshwater pearl recovery in the United States, Tennessee being first.

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.

Arkansas is often thought of as offering little material for the lapidary, other than quartz crystal and diamond. However, for the hobbyist interested in tumble polishing and cabochon making, much useful material is present.


Agate
Agate is translucent cryptocrystalline quartz which displays distinct banding. Most agate collected in Arkansas is present in gravel deposits on Crowley's Ridge, although agate can occur wherever gravel is present. Crowley's Ridge extends north-south from Clay County to Phillips County in a gentle eastward-facing arc. The agates in this area are different shades of tan, light brown, and yellow due to the penetration and oxidation of trace amounts of iron. The gravels of the Crowley's Ridge deposits were transported to their present position by the ancestral Mississippi River. Identically banded, light bluish-gray agate is present in Missouri in the Potosi Formation (Upper Cambrian). This rock unit may be the source of the bulk of the agate in the Crowley's Ridge deposits. Oxidation of the gravel-bearing units has altered the original blue-gray color to shades of brown and yellow. Rarely, a specimen may appear similar to the agate from the Great Lakes area of the northern United States. Agate is also moderately common at the Crater of Diamonds State Park, where it sometimes displays a lace-like pattern. The agate is present as blocky rectangular pieces weighing up to several pounds and is present in the major drainages of the diamond-search area. They are somewhat sugary or porous in texture, rendering it unusable to the lapidary. However, good-quality pieces are not uncommon and yield attractive cabochons in a variety of colors, some being suitable for tumble polishing.


Amethyst
Amethyst as a gem material is a violet to purple, transparent, crystalline variety of quartz. The Crater of Diamonds State Park, 2.5 miles southeast of Murfreesboro in Pike County, is the only area in Arkansas known to contain crystals of amethyst large enough to be of use to the lapidary. Amethyst veins, some a foot wide, are sometimes located by collectors during the periodic plowing of the diamond search area. The amethyst is present as stubby strongly colored crystals up to 1 inch across, filling cavities in calcite veins. Individual specimens are scarce and the amethyst crystals may be zoned or contain tiny inclusions of goethite (an iron mineral), strongly resembling the amethyst of Brazilian geodes. Although some percentage of this amethyst may be faceting quality, most is suitable for producing tumbled stones.


Chalcedony
Chalcedony is a light-colored, translucent, nonbanded variety of cryptocrystalline quartz which has a waxy luster on a broken surface. It is often nodular and sometimes is fluorescent green in ultraviolet light. Cream-colored masses of chalcedony reportedly have been recovered from the gravel deposits of the Saline River in Saline County.


Chert
Chert is an opaque to translucent cryptocrystalline variety of quartz, which ranges considerably in color and suitability for lapidary use. Although the Ouachita Mountains contain major beds of sedimentary chert, very little is of cuttable quality. Major sedimentary units in northern Arkansas do contain banded translucent nodules of chert that will take a high polish when tumbled or cut into cabochons. Nodular chert in the Cotter Formation (Early Ordovician) and in the residuum formed by its weathering is often available in attractively banded pieces. Large unfractured examples are somewhat scarce, but abundant tumbling-quality material is available, particularly in Marion County, and also in portions of Carroll, northern Boone, Baxter, Fulton, Randolph, Sharp, and Izard Counties. This is the major outcrop area of the Cotter Formation. Some chert which will take a high polish is also present in the Penters Formation (Devonian) and, locally, in the Boone Formation (Mississippian) and its residuum in north Arkansas. All of these materials are present in shades of brown, tan, cream, and gray. Large quantities of tan to brown chert are also present in the gravel deposits along Crowley's Ridge.


Jasper
Jasper is a red variety of chert. Two companies, one in Pike County and the other in Hempstead County, have reported the recovery of small quantities (less than 1,000 pounds yearly) of jasper for several years. The suitability of this material for lapidary use is unknown. The source of the jasper may be the basal gravel deposits of the Cretaceous formations or Quaternary deposits which contain reworked gravels derived from the Cretaceous units. The jasper probably originated as red novaculite. Jasper is also present at the Crater of Diamonds State Park, Pike County, as rounded reddish-brown to red surficial gravels in the diamond search area. The jasper takes a high polish and may be used for tumbling and cabochon making. Small amounts of jasper is present in the gravel deposits of Crowley's Ridge in northeast Arkansas.


Opal
Although opal is not quartz mineralogically, it is discussed here because it is an amorphous variety of silica (SiO2) and can occur anywhere ground water has circulated. Opal usually contains an indeterminate quantity of water so the chemical formula is written as SiO2. nH2O. A colorless transparent variety called hyaline is relatively common in Arkansas as late-formed glassy blebs or crusts coating other minerals. Hyaline is commonly fluorescent green due to traces of uranium salts. No site in Arkansas has yielded significant material for lapidary use.

At the Potash Sulphur Springs intrusion in Garland County, late secondary opal was discovered in the zone of contact metamorphism as both greenish-yellow veins having black dendritic (fern-like) patterns and as gray, opalized replacements of the contact rocks. In the North Wilson pit at this site, paper-thin films of fiery precious opal were noted in a very restricted zone in the vanadium orebody.

In southern and eastern Arkansas, wherever petrified wood is present, there is the possibility of discovering late-formed hyaline opal. See the section on Petrified Wood.


Petrified Wood
Silicified petrified wood is present in Quaternary gravel deposits in eastern and southern Arkansas. Because most specimens are cream to white in color, little interest has been expressed by hobbyists in cutting and polishing the material. A fossilized "logjam" of this type of petrified wood was reported in a stream drainage at the golf course of the El Dorado Country Club in Union County. Many people in southern Arkansas use light-colored petrified wood as flower-garden decoration pieces or borders. Late-formed hyaline is often present as colorless botryoidal infillings of cavities or fractures in the petrified wood. Some petrified wood in the gravel deposits along Crowley's Ridge ranges in color from tan and brown to black and takes a high polish. This material is suitable for cabochon making and tumble polishing. Numerous small pieces and sometimes large logs of petrified wood are collected in the creeks that drain Crowley's Ridge from Forrest City in St. Francis County northward to Wynne in Cross County

Rock Crystal
Rock crystal (quartz crystal) that qualifies as a gem material is transparent, colorless and should contain no visible flaws. This material is relatively abundant at several quartz crystal dealers in Arkansas and the price varies with size of the rough stock. When used for faceting stones or beads, carving figures or decorative items, or manufacturing spheres, it is not necessary that the crystal's exterior be undamaged as with prime specimen material. Because of the low price of surface-damaged rock crystal, it is a popular material to use when learning faceting techniques. Faceted rock crystal is sold at many tourist-based businesses in Arkansas under the trade name, "Hot Springs diamond". Slender, clear, undamaged single quartz crystals are known locally as jewelry points and are used in the manufacture of relatively inexpensive necklace drops, pendants, and earrings, often set in sterling silver settings. Rock crystal for this use ranges from $30 to more than $150 per pound, depending on its perfection, transparency, luster, and length of the crystals.


Smoky Quartz
Smoky quartz as a gem material is light- to medium-brown in color, transparent, and of best quality when it is unzoned (uniform color). In Arkansas, most smoky quartz is present in two areas: near Jessieville in Garland County and adjacent to the Magnet Cove intrusion in Hot Spring County. Southwest of Jessieville, one mining operation occasionally recovers some pale- to medium-brown smoky quartz. These crystals range up to 3 inches in length and 1.5 inches across and have milky bases or areas near their attachment points to the vein walls. Most crystals exhibit faint zoning (alternating light and dark banding), but some crystals qualify as faceting material. Zoned and unzoned smoky quartz crystals to 6 inches long were mined in the late 1960’s at a site on the north shore of Lake Ouachita, west of Jessieville in Garland County. The area has since been closed to collecting by the U. S. Army Corps of Engineers. The deposits of smoky quartz at Magnet Cove have been known for over a century. The host rock, the Arkansas Novaculite (Mississippian-Devonian), is the source of the silica that was necessary to form the crystals. In this area, smoky quartz crystals have been discovered up to 15 inches in length and 6 inches across. Most of the smoky quartz from this area contains either internal fractures, zoning, mineral inclusions, or has sufficient internal stress that renders it useless for faceting stock. Small pieces are sometimes cut into attractive gems. Some of this material might be useful for tumbled stones. A site which yielded a small amount of faceting-grade smoky quartz was discovered by Ben Clardy, Arkansas Geological Commission, and investigated by state geologists in the 1970’s. It was a highly weathered quartz syenite dike in a bauxite mine in Saline County. Although about 50 pounds of rough smoky quartz pieces were collected, less than a pound was of faceting quality.

Most mineral dealers and rock shops in Arkansas have samples of "smoky quartz" on display. Much of this material is natural rock crystal that has been subjected to gamma radiation in a reactor, causing the crystal to turn almost black. Quartz dealers have been marketing this irradiated quartz for many years, largely for decorative purposes.


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.


Barwood, H. L., and deLinde, H. S., 1989, Arkansas phosphate minerals, a review and update: Rocks and Minerals, v. 64, no. 4, p. 294-299.
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.
Kidwell, A. L., 1977, Iron phosphate minerals of the Ouachita Mountains, in Stone, C. G., ed., Symposium on the geology of the Ouachita Mountains, v. II,: Arkansas Geological Commission Miscellaneous Publication 14, p. 50-62.
Kidwell, A. L., 1990, Famous mineral localities – Murfreesboro, Arkansas: The Mineralogical Record, v.21, p. 545-555.
Kunz, G. F., and Stevenson, C. H., 1908, The book of the pearl: The history, art, science, and industry of the queen of gems: New York, Century Company [reprinted 1993 by Dover Publications, Inc., New York], p. 263-278.
Miser, H. D., 1959, Structure and vein quartz of the Ouachita Mountains of Oklahoma and Arkansas, in Cline, L.M. and others, The geology of the Ouachita Mountains – A symposium: Dallas Geological Society and Ardmore Geological Society, p. 30-43.
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.
Schumann, Walter, 1977, Gemstones of the world: New York, Sterling Publishing, 256 p.
Sinkankas, John, 1972, Gemstone & mineral data book: New York, Van Nostrand-Reinhold (paperback edition of 1981), 352 p.
Smith, A. E., Jr., 1985, The aluminum phosphate minerals from Mauldin Mountain, Montgomery County, Arkansas: Mineralogical Record, v. 16, p. 291-295.
Stockard, S. W., 1904, History of pearls and pearling in Arkansas, in History of Lawrence, Jackson, and Independence Counties of the third Judicial District of Arkansas: Little Rock, Arkansas Democrat Company [reprinted 1986 by Morgan Books, Newport, Ark.], p. 166-171.

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Greensand

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.
Dane, C. H., 1929, Upper Cretaceous formations of southwestern Arkansas: Arkansas Geological Survey Bulletin 1, 215 p.

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Gypsum

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.
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.
Pierson, F. L., 1974, The Weyerhauser gypsum mining operation at Briar, Arkansas, in Arkansas-Texas Economic Geology Field Trip: Arkansas Geological Commission Guidebook 74-1, p. 17-18.

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Limestone

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 2,000° 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.
Corbin, M. W., and Heyl, G. R., 1941, Tertiary limestones of Pulaski and Saline Counties, Arkansas: Arkansas Geological Survey Information Circular 13, 28 p.
Croneis, Carey, 1930, Geology of the Arkansas Paleozoic area, with especial reference to oil and gas possibilities: Arkansas Geological Survey Bulletin 3, 457 p.
Holbrook, D. F., 1965, High-calcium limestones in Independence and Izard Counties, Arkansas: Arkansas Geological Commission open-file report, 21 p.
Hopkins, T. C., 1893, Marbles and limestones: Arkansas Geological Survey Annual Report for 1890, v. IV, 443 p.

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Marble

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.
Parks, Bryan, and Hansell, J. M., 1932, Black marbles of northern Arkansas: Arkansas Geological Survey Information Circular 3, 51 p.

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Marl

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.
Dane, C. H., 1929, Upper Cretaceous formations of southwestern Arkansas: Arkansas Geological Survey Bulletin 1, 215 p.
Taff, J. A., 1902, Chalk of southwestern Arkansas with notes on its adaptability to the manufacture of hydraulic cements: U. S. Geological Survey 22nd Annual Report, 1900-1901, pt. 3, p. 687-742.

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Nepheline Syenite

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.
Morris, E. M., 1987, The Cretaceous Arkansas alkalic province; A summary of petrology and geochemistry, in Morris, E. M. and Pasteris, J. D., eds., Mantle metasomatism and alkaline magmatism: Geological Society of America Special Paper 215, p. 217-233.
Smothers, W. J., Williams, N. F., and Reynolds, H. J., 1952, Ceramic evaluation of Arkansas nepheline syenite: Arkansas Resources and Development Commission, Division of Geology Information Circular 16, 21 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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Novaculite (Silica Stone)

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.

Although the Arkansas Novaculite formation is widely distributed in the Ouachita Mountains of Arkansas, deposits of commercial interest are located along the southern edge of the Benton – Broken Bow Uplift. Because it is highly resistant to erosion, it forms prominent ridges. The formation of Devonian and Mississippian age consists of massive upper and lower divisions of novaculite interbedded with a middle division of thinly bedded novaculite and shale. Its stratigraphic thickness ranges from about 60 feet in the north to 900 feet in the southern Ouachita Mountains, but may be greater on outcrop due to repetitive faulting.

Arkansas novaculite is recognized worldwide for its use as whetstones and oilstones, which are used for sharpening knives, surgical instruments, and wood-carving tools. In the early 1800’s, a quarry of honestone near Magnet Cove in Hot Spring County was mined by early settlers. Records show that novaculite mining in Arkansas was intermittent from 1885 to 1905, but continuous ever since.

Novaculite for abrasives is mined mostly in Garland and Hot Spring Counties. It is classified by the abrasives industry into two general categories: "Arkansas" stone and "Washita" stone. "Arkansas" stone is extremely fine-grained, uniform, has a waxy luster, and is typically white or light gray. "Washita" stone is less dense, more porous, and has the dull luster of unglazed porcelain. When quarrying novaculite for whetstones, little or no explosives (and then only black powder) are used because blasting, combined with the brittle nature of the stone, tends to cause excessive fracturing, reducing the amount of useful stone. Rough novaculite blocks are cut by circular diamond saws, using large amounts of degradable lubricant or water as a coolant. The preformed stones are lapped (smoothed) on horizontal rotating grinding machines, using industrial abrasive grits, such as silicon carbide.

Commercial whetstone mines were active in Arkansas until the development of less costly synthetic abrasives. Following an industry slump, the demand for natural honestones and oilstones has increased over the past two decades, resulting in increased quarry output. In 2007, there were 8 companies that mined and processed whetstones in the Hot Springs area. The tonnage of novaculite mined for abrasives applications is withheld to avoid disclosing company proprietary data.  Interest in novaculite as oilstones has increased in recent years, due to it being viewed as a more “natural” product than synthetic alternatives.

Other uses of novaculite have included concrete aggregate, road construction material, railroad ballast, riprap, high-silica refractories, and for the recovery of silicon metal. The massive novaculite of the Upper and Lower Divisions of the Arkansas Novaculite is a source of high-purity silica (>99 percent). Individual quarries for novaculite extend from Little Rock in Pulaski County westward to Hatton in Polk County.

There is an extensive, uncalculated, resource of massive novaculite in the Ouachita Mountains. However, top-quality whetstone-grade material appears to be restricted to Garland and Hot Spring Counties. The available tonnage is quite variable from one deposit to another. The market for natural whetstones and oilstones should continue to increase, but competition by other natural and manufactured abrasives may prevent rapid expansion. In 2005, Arkansas ranked 1st in the nation in silica stone (abrasives) production.

Griswold, L. S., 1892, Whetstones and the novaculites of Arkansas: Arkansas Geological 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.
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.
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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Arkansas Geological Survey
Vardelle Parham Geology Center
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Little Rock, AR 72204
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