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36-539: Paradox Valley is a basin located in western Montrose County in the U.S. state of Colorado . The dry, sparsely populated valley is named after the apparently paradoxical course of the Dolores River —instead of flowing down the length of the valley, the river cuts across the middle and through the sheer walls of large mesas on either side. The valley is the site of a Bureau of Reclamation salinity -control project which has caused thousands of earthquakes, and

72-476: A salt dome . The salt may not have actually been exposed on the surface, but groundwater entering the top of the dome dissolved the underlying salt beds, allowing the center to collapse, forming what is today Paradox Valley. This process took place over about 150 million years, a long enough time for the Dolores River to downcut into the land and maintain its ancient course . The same process also created

108-512: A fertilizer. Gypsum may act as a source of sulfur for plant growth, and in the early 19th century, it was regarded as an almost miraculous fertilizer. American farmers were so anxious to acquire it that a lively smuggling trade with Nova Scotia evolved, resulting in the so-called "Plaster War" of 1820. Gypsum is moderately water-soluble (~2.0–2.5 g/L at 25 °C) and, in contrast to most other salts, it exhibits retrograde solubility, becoming less soluble at higher temperatures. When gypsum

144-551: A high-pressure injection well , where it is deposited 14,000 to 16,000 feet (4,300 to 4,900 m) deep into Precambrian and Paleozoic rocks. A 2001 study found that the total salt reaching the Dolores had declined by about 90%, although this may have been the result of a period of low precipitation during the measurement period. As of 2009, the PVU removes about 113,000 tons of salt annually from Paradox Valley. The injection well of

180-474: A range of industrial processes. Flue gas desulfurization gypsum (FGDG) is recovered at some coal-fired power plants. The main contaminants are Mg, K, Cl, F, B, Al, Fe, Si, and Se. They come both from the limestone used in desulfurization and from the coal burned. This product is pure enough to replace natural gypsum in a wide variety of fields including drywalls, water treatment, and cement set retarder. Improvements in flue gas desulfurization have greatly reduced

216-413: A result, waste gypsum is stored in stacks indefinitely, with significant risk of leaching their contaminants into water and soil. To reduce the accumulation and ultimately clear out these stacks, research is underway to find more applications for such waste products. People can be exposed to gypsum in the workplace by breathing it in, skin contact, and eye contact. Calcium sulfate per se is nontoxic and

252-543: A wide range of colors to local deposits. Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, the unique conditions of the White Sands National Park in the US state of New Mexico have created a 710 km (270 sq mi) expanse of white gypsum sand, enough to supply the US construction industry with drywall for 1,000 years. Commercial exploitation of

288-423: Is a collapsed anticline , a type of geological fold . About 300 million years ago, during the middle Pennsylvanian period, when the Dolores River was already in existence, high pressures on lands to the northeast caused underlying salt deposits to flow towards where the valley is today. The salt encountered a buried fault-block ridge and was deflected upwards, penetrating the overlying rock strata and forming

324-510: Is contaminated by impurities found in the rock, namely fluoride , silica , radioactive elements such as radium , and heavy metal elements such as cadmium . Similarly, production of titanium dioxide produces titanium gypsum (TG) due to neutralization of excess acid with lime . The product is contaminated with silica, fluorides, organic matters, and alkalis. Impurities in refinery gypsum waste have, in many cases, prevented them from being used as normal gypsum in fields such as construction. As

360-448: Is even approved as a food additive, but as powdered gypsum, it can irritate skin and mucous membranes. The Occupational Safety and Health Administration (OSHA) has set the legal limit ( permissible exposure limit ) for gypsum exposure in the workplace as TWA 15 mg/m for total exposure and TWA 5 mg/m for respiratory exposure over an eight-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set

396-593: Is heated in air it loses water and converts first to calcium sulfate hemihydrate ( bassanite , often simply called "plaster") and, if heated further, to anhydrous calcium sulfate ( anhydrite ). As with anhydrite , the solubility of gypsum in saline solutions and in brines is also strongly dependent on sodium chloride (common table salt) concentration. The structure of gypsum consists of layers of calcium (Ca ) and sulfate ( SO 2− 4 ) ions tightly bound together. These layers are bonded by sheets of anion water molecules via weaker hydrogen bonding , which gives

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432-462: Is prized for ornamental work of various sorts. In arid areas, gypsum can occur in a flower-like form, typically opaque, with embedded sand grains called desert rose . It also forms some of the largest crystals found in nature, up to 12 m (39 ft) long, in the form of selenite. Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks . Deposits are known to occur in strata from as far back as

468-500: Is the proposed location of a new uranium mill which would be the first built in the United States in over 25 years. Paradox Valley trends northwest-southeast and measures about 3 to 5 miles (5 to 8 km) wide and 25 miles (40 km) long. It lies along the extreme western edge of Colorado , close to the border with Utah , about 50 miles (80 km) south of the city of Grand Junction . The La Sal Range rises just to

504-498: The Archaean eon . Gypsum is deposited from lake and sea water, as well as in hot springs , from volcanic vapors, and sulfate solutions in veins . Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near-surface exposures. It is often associated with the minerals halite and sulfur . Gypsum is the most common sulfate mineral. Pure gypsum is white, but other substances found as impurities may give

540-717: The Byzantine Empire , and the Nottingham alabasters of Medieval England . The word gypsum is derived from the Greek word γύψος ( gypsos ), "plaster". Because the quarries of the Montmartre district of Paris have long furnished burnt gypsum ( calcined gypsum) used for various purposes, this dehydrated gypsum became known as plaster of Paris . Upon adding water, after a few dozen minutes, plaster of Paris becomes regular gypsum (dihydrate) again, causing

576-790: The Mars Reconnaissance Orbiter (MRO) have indicated the existence of gypsum dunes in the northern polar region of Mars, which were later confirmed at ground level by the Mars Exploration Rover (MER) Opportunity . Commercial quantities of gypsum are found in the cities of Araripina and Grajaú in Brazil; in Pakistan, Jamaica, Iran (world's second largest producer), Thailand, Spain (the main producer in Europe), Germany, Italy, England, Ireland, Canada and

612-655: The Moab Valley ( Spanish Valley ) to the west, itself cut crosswise in a similar fashion by the Colorado River . The Paradox Formation , a geological formation containing salt , gypsum , anhydrite , shale , sandstone , and limestone , is named after exposures found in Paradox Valley. The Paradox Basin , a geologic province throughout which the Paradox Formation is found, also bears

648-494: The Paradox Valley Unit has induced thousands of earthquakes , including at least 4,000 prior to the year 2001. Most were below the threshold of human detection, but at least 15 have been over 2.5 in magnitude , the largest being a 4.3 magnitude quake on May 27, 2000. The PVU suspended operations for 28 days following this quake, but later resumed injections at a lower rate. Further earthquakes have been linked with

684-637: The United States. Large open pit quarries are located in many places including Fort Dodge, Iowa , which sits on one of the largest deposits of gypsum in the world, and Plaster City, California , United States, and East Kutai , Kalimantan , Indonesia. Several small mines also exist in places such as Kalannie in Western Australia , where gypsum is sold to private buyers for additions of calcium and sulfur as well as reduction of aluminum toxicities on soil for agricultural purposes. Crystals of gypsum up to 11 m (36 ft) long have been found in

720-495: The amount of toxic elements present. Gypsum precipitates onto brackish water membranes , a phenomenon known as mineral salt scaling , such as during brackish water desalination of water with high concentrations of calcium and sulfate . Scaling decreases membrane life and productivity. This is one of the main obstacles in brackish water membrane desalination processes, such as reverse osmosis or nanofiltration . Other forms of scaling, such as calcite scaling, depending on

756-418: The area, strongly opposed by area residents, was permanently prevented in 1933 when President Herbert Hoover declared the gypsum dunes a protected national monument . Gypsum is also formed as a by-product of sulfide oxidation , amongst others by pyrite oxidation , when the sulfuric acid generated reacts with calcium carbonate . Its presence indicates oxidizing conditions. Under reducing conditions,

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792-489: The caves of the Naica Mine of Chihuahua , Mexico. The crystals thrived in the cave's extremely rare and stable natural environment. Temperatures stayed at 58 °C (136 °F), and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs 55 tonnes (61 short tons) and is around 500,000 years old. Synthetic gypsum is produced as a waste product or by-product in

828-672: The crystal perfect cleavage along the sheets (in the {010} plane). Gypsum occurs in nature as flattened and often twinned crystals , and transparent, cleavable masses called selenite . Selenite contains no significant selenium ; rather, both substances were named for the ancient Greek word for the Moon . Selenite may also occur in a silky, fibrous form, in which case it is commonly called "satin spar". Finally, it may also be granular or quite compact. In hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly tinted variety of gypsum, called alabaster ,

864-522: The land to settlement. Springs and streams allowed farming in the northwest end of the valley, and the mid-1890s discovery of copper at the future site of the Cashin Mine near the town of Bedrock brought in a further influx of settlers. The valley and the surrounding plateau soon also became an important source of radioactive materials, including radium and uranium . In 1913, The New York Times identified carnotite mines near Paradox Valley as

900-542: The main constituent in many forms of plaster , drywall and blackboard or sidewalk chalk . Gypsum also crystallizes as translucent crystals of selenite . It forms as an evaporite mineral and as a hydration product of anhydrite . The Mohs scale of mineral hardness defines gypsum as hardness value 2 based on scratch hardness comparison . Fine-grained white or lightly tinted forms of gypsum known as alabaster have been used for sculpture by many cultures including Ancient Egypt , Mesopotamia , Ancient Rome ,

936-586: The material to harden or "set" in ways that are useful for casting and construction. Gypsum was known in Old English as spærstān , "spear stone", referring to its crystalline projections. Thus, the word spar in mineralogy, by comparison to gypsum, refers to any non- ore mineral or crystal that forms in spearlike projections. In the mid-18th century, the German clergyman and agriculturalist Johann Friderich Mayer investigated and publicized gypsum's use as

972-578: The name of the valley. Paradox Valley was within the historical domain of the Ute tribe . An 1868 treaty created a reservation for the Utes over much of western Colorado, including Paradox Valley. Squatters began grazing cattle in the valley as early as 1877, in violation of the treaty. By 1881, the Utes had been forced out of the area, and in 1882 the United States Congress officially opened

1008-587: The northwest in Utah. State Highway 90 follows Paradox Valley on its way from Naturita to the Utah state line, crossing the Dolores River Bridge near the small unincorporated town of Bedrock . The town of Paradox lies a few miles north of the highway. Elevations on the valley floor range from about 5,000 feet (1,500 m) at the Dolores River to nearly 6,000 feet (1,800 m) at the southeast end. Steep parallel sandstone and shale walls bound

1044-495: The operation, including a 3.9 magnitude quake in 2004. In 2009 Energy Fuels Resources Corporation, a subsidiary of Toronto -based Energy Fuels Incorporated, proposed the construction of a uranium mill in the southeast end of Paradox Valley. Called the Piñon Ridge Mill, it would have been capable of processing 500 tons of uranium ore per day. Legal action tied up the project for many years, and as of September 2020

1080-887: The opposite wall. As a consequence of this unusual geography, the valley cannot be easily irrigated by the Dolores River, but springs and streams fed by snowmelt from the La Sal Range support farming in the northwestern third of the valley. Near the center of the valley, the town of Bedrock experiences average highs ranging from 45 °F (7 °C) in December to 96 °F (36 °C) in July. Average lows range from 13 °F (−11 °C) in December to 54 °F (12 °C) in July. An average of 11 inches (28 cm) of precipitation, including 9 inches (23 cm) of snow, fall annually at Bedrock. The apparent paradox of Paradox Valley can be explained by salt tectonics . The valley

1116-416: The project appears to have died. Depression (geology) Erosion -related: Collapse-related: Impact-related: Sedimentary-related: Structural or tectonic-related: Volcanism-related: Gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate , with the chemical formula CaSO 4 ·2H 2 O . It is widely mined and is used as a fertilizer and as

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1152-534: The source of "the greatest radium ore deposits in the world". Production of radium ceased in 1922 when richer deposits were found in the Belgian Congo , but production of uranium and vanadium continued throughout most of the century. Near-surface salt beds up to 14,000 feet (4,300 m) thick still underlie Paradox Valley. The Dolores River, a tributary of the Colorado River , naturally picks up about 100,000-200,000 tons of salt annually on its way through

1188-451: The sulfates it contains can be reduced back to sulfide by sulfate-reducing bacteria . This can lead to accumulation of elemental sulfur in oil-bearing formations, such as salt domes, where it can be mined using the Frasch process Electric power stations burning coal with flue gas desulfurization produce large quantities of gypsum as a byproduct from the scrubbers. Orbital pictures from

1224-420: The valley to the northeast and southwest. The valley was named in 1875 by geologist and surveyor Albert Charles Peale after he noted that the Dolores River had a "desire to perform strange and unexpected things" in the area. Instead of flowing down the valley's thalweg , the river emerges from a narrow gap in one wall, cuts perpendicularly across the mostly level valley floor, and exits through another gap in

1260-580: The valley. In the 1980s, the United States Bureau of Reclamation began construction of a pumping facility known as the Paradox Valley Unit. The PVU, a part of the wider Colorado River Basin Salinity Control Project , became fully operational in 1996 and collects saline groundwater from 12 shallow wells along the Dolores River. The system then dilutes the brine with water and a corrosion inhibitor and transports it to

1296-561: The water source, can also be important considerations in distillation , as well as in heat exchangers , where either the salt solubility or concentration can change rapidly. A new study has suggested that the formation of gypsum starts as tiny crystals of a mineral called bassanite (2CaSO 4 ·H 2 O). This process occurs via a three-stage pathway: The production of phosphate fertilizers requires breaking down calcium-containing phosphate rock with acid, producing calcium sulfate waste known as phosphogypsum (PG). This form of gypsum

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