Clay Canyon variscite is the classic American cabinet form of the species: polished nodules and slabs of dense apple- to chrome-green AlPO4·2H2O, cut by yellow crandallite and dotted or veined with gray-green wardite and other late phosphate minerals. The best pieces have the look of a miniature geological map—green islands, yellow rinds, pale seams, and occasional pockets—rather than the uniform cabochon rough that most gem buyers associate with variscite. For serious mineral collectors, that texture is the locality’s signature.
Photo: Wikimedia Commons
The mine’s fame rests on more than beauty. Clay Canyon, near Fairfield in the Sunshine Mining District of Utah County, is one of the great phosphate-mineral localities of North America. The deposit is a former underground gemstone and phosphate occurrence in altered limestone, best known under the Little Green Monster name but historically also tied to the Clay Canyon, Utahlite, and Chlorutahlite mine names. Its nodules are not simply variscite; they are mineralogical capsules in which variscite was overprinted, replaced, fractured, and refilled by a remarkable suite of hydrous aluminum, calcium, sodium, magnesium, strontium, and scandium phosphates.
The locality has type-locality status for a cluster of phosphate minerals that grew out of the scientific study of these nodules, including englishite, gordonite, millisite, montgomeryite, overite, and wardite. That concentration of species is why a polished Clay Canyon nodule can belong equally well in a gem cabinet, a phosphate systematic suite, or a collection of classic American localities.
The field setting is just as distinctive. The Clay Canyon deposits are hosted by dark limestone and black shale of the Upper Mississippian Great Blue Limestone, above the Long Trail Shale Member, on the northwestern limb of the Ophir anticline. At the Little Green Monster deposit, variscite nodules replaced limestone along a north-trending vertical fracture zone, occurring in pipe-like bodies that plunge north. The phosphate bodies are tied to brecciated and fractured carbonate rock, with alteration minerals including limonitic clay, alunite, chalcedonic quartz, and calcite.
Collectors look for vivid green variscite cores, strong yellow crandallite borders, gray-green wardite spheres or seams, and a clean polish that reveals the whole internal structure of the nodule. A specimen with locality-provenanced old labels, especially one traceable to the Ed Over–Arthur Montgomery era or to older museum/dealer dispersals, carries a premium beyond its lapidary beauty.
Search for specimens: View all variscite specimens from Clay Canyon Mine, Utah, USA
The Clay Canyon variscite locality lies near Fairfield, Utah, in the Sunshine Mining District of Utah County, on the south side of the Oquirrh Mountains. The collecting name most often encountered on labels is Little Green Monster Variscite Mine, though older and commercial labels may read Clay Canyon, Clay Canyon Variscite Mine, Utahlite Mine, Chlorutahlite Mine, Fairfield, or simply “Utah variscite.” Those names are not interchangeable for every Utah variscite occurrence, but in the classic green-and-yellow nodular material they commonly point back to this Clay Canyon mine area.
Geologically, the deposit belongs to a western Utah–Nevada class of scandium-bearing aluminum phosphate deposits characterized by variscite, crandallite, wardite, kolbeckite, and related minerals. In Clay Canyon, three separate variscite occurrences have been described: the Little Green Monster deposit and two unnamed deposits. At Little Green Monster, variscite and crandallite occur as nodular aggregates in highly altered matrix, elongate replacements along fractures, and fissure fillings. At the western Clay Canyon occurrence, variscite was reported both as nodules in brecciated limestone and as vug fillings in jasperoid.
The paragenesis is central to understanding the specimens. The earliest major event was replacement of limestone by variscite. Crandallite then largely replaced earlier variscite, producing the yellow rinds and internal yellow seams so characteristic of polished Clay Canyon nodules. Rare phosphate minerals accompanied and followed this crandallite alteration, with quartz, calcite, and limonite coming later. That sequence explains why an attractive slab is often both gem material and a cross-section through a complex phosphate alteration history.
The mining history begins in the late nineteenth century. Variscite from the Clay Canyon deposit was brought to scientific attention in 1893, when F. T. Millis of Lehi, Utah, sent a specimen to George P. Merrill at the U.S. National Museum. Don Maguire later mined and marketed the green stone on a small scale for jewelry under names such as chlor-utahlite; early production was modest, and the yellow companion material also entered the trade under the name sabalite.
The locality’s great collecting period came with Arthur Montgomery and Edwin Over. In 1936 they staked the Little Green Monster claim, fresh from work at Green Monster Mountain on Prince of Wales Island, Alaska, and the name followed them to Utah. In 1937, and apparently again in 1939, they mined thousands of pounds of phosphate nodules. Much of that material went to major institutions, dealers, and serious collectors, which is why old Clay Canyon slabs still appear with museum-style or early dealer provenance.
The deposit also drew economic interest for scandium. Scandium-bearing minerals were identified in association with the variscite nodules, and beginning in 1959 the Kawecki Chemical Company investigated the deposits as a possible scandium source. Two shipments of crandallite ore, weighing about 330 and 4,000 pounds, were produced in 1959 and 1960. Those shipments were not the beginning of a sustained collector-specimen renaissance, but they reinforced the locality’s unusual geochemical importance.
Collecting access today should be treated as effectively closed for practical purposes. The mine is reclaimed, the old entrances and dumps have been bulldozed to match the surrounding hillside contours, and little of the original working locality can now be recognized on the ground. Anyone considering a visit would need current land and mineral-rights permission and should not expect productive collecting.
Photo: Wikimedia Commons
Variscite from Clay Canyon occurs as compact, microcrystalline nodules rather than as visible crystals. Larsen’s classic study described the Fairfield nodules as ranging from about a quarter inch to two feet or more in diameter, with the commonest size from one to three inches. They are commonly spherical, sometimes flattened, and occasionally show contact interference where adjacent nodules grew against one another. Some material occurs as angular fragments, interpreted as broken pieces of earlier nodules.
Color is the first quality marker. The best Clay Canyon variscite is saturated apple green to chrome green, sometimes with a bluish cast. The color may appear in rounded cores, segmented pods, broken islands, or irregular masses enclosed by secondary phosphate material. Lower-grade pieces may be paler, more porous, more altered to crandallite, or diluted by matrix.
The second quality marker is the pattern. Most distinctive polished nodules show a yellow crandallite rind around green variscite, and many are cut by additional yellow crandallite seams. Gray-green wardite may appear as small rounded spots, spheres, or patches within the nodule structure. On fine slabs the relationship is crisp: green variscite fields, yellow crandallite borders, gray-green wardite accents, and sometimes pale or whitish phosphate crusts and cavity fillings.
Associated minerals at the Little Green Monster/Clay Canyon locality include crandallite, wardite, englishite, gordonite, millisite, montgomeryite, overite, kolbeckite, goyazite, fluorapatite, hydroxylapatite, alunite, calcite, quartz, limonitic material, and related phosphate phases. For most collectors, the practical associated-mineral trio on display-quality slabs is variscite-crandallite-wardite; for systematic collectors, the real prize may be small cavities and alteration zones containing the rarer phosphates.
Clay Canyon variscite is generally valued as a polished specimen rather than as a loose gemstone rough. A high-end piece should have strong color, good contrast between green and yellow, a readable nodule structure, and minimal undercutting or pitting from differential hardness and porosity. A full half-nodule or thick slab with both an attractive polished face and natural nodule context is generally more desirable than a thin, anonymous cabbing slice.
Size adds importance, but only if the color and pattern hold together. Small, vivid polished nodules are often better than large, dull ones. Large cabinet slabs with sharp green-and-yellow architecture, especially those several inches across and accompanied by old labels, occupy the top tier of Clay Canyon material.
The first authenticity issue is locality precision. “Utah variscite” is not automatically Clay Canyon. Utah has produced notable variscite from several areas, including Fairfield/Clay Canyon, Lucin, and other western Utah occurrences. Clay Canyon material is especially recognizable by its nodular green variscite with yellow crandallite rinds and seams, commonly with gray-green wardite. Lucin material and other Utah variscites can be handsome in their own right, but they should not be sold as Clay Canyon unless the provenance is solid.
The second issue is the turquoise problem. Variscite and turquoise overlap in color, use, and market vocabulary, and green variscite has long been substituted for or confused with turquoise in jewelry. Clay Canyon material, however, usually tells on itself in polished specimen form: the yellow crandallite rind and internal phosphate veining are far more typical of Clay Canyon nodules than of ordinary turquoise. In cabochons cut from isolated green areas, that diagnostic context can disappear, making provenance and documentation more important.
Treatments should be watched for in gem and jewelry material. Variscite is porous enough to absorb oils, waxes, polymers, and other stabilizing or color-altering substances, and doublets are documented in the broader variscite gem trade. For Clay Canyon collector specimens, the usual desirable finish is a clean mechanical polish on natural nodule material. Any resin filling, backing, dye, stabilization, or reconstructed slab should be disclosed.
Condition issues are predictable for a mixed phosphate nodule. Variscite, crandallite, wardite, and associated alteration minerals can polish differently, producing undercut seams, soft-looking yellow areas, pits, or open cavities. Thin slabs may be fragile along old fractures or crandallite-rich seams. Natural fractures are common and not automatically fatal, but repaired breaks, glued slices, or polished faces that obscure losses should be evaluated carefully.
Rarity is real. The classic mine is reclaimed, old dumps and portals are gone, and the great collecting and mining periods are long past. Most available specimens are old-stock polished nodules, slices, halves, and occasional rough fragments released from collections or dealer inventories. Fine polished slices and half-nodules have brought strong prices, with top pieces valued as serious cabinet minerals rather than casual lapidary curiosities.
The best buying strategy is to prioritize documentation. A Clay Canyon specimen with an old label, collection history, or dealer record is preferable to a loose green-yellow slab of uncertain source. Look for labels naming Little Green Monster, Clay Canyon, Fairfield, Utah County, Arthur Montgomery, Ed Over, Smithsonian-related dispersals, Harvard-related material, or long-established mineral dealers. The material is distinctive, but provenance is what turns a pretty variscite slice into a classic locality specimen.
The Clay Canyon story begins with a false glitter. In 1893, Frank Butt and his brother thought they had found gold in Clay Canyon. They had not. The “gold” excitement faded, but one of the odd green nodules made its way to F. T. Millis of Lehi, who sent material to George P. Merrill at the U.S. National Museum. The supposed prospect became something more durable than a small gold rush: a mineralogical locality that would keep specialists busy for decades.
Don Maguire took up the deposit around 1904 and tried to sell the green stone as a turquoise-like gem. The commercial reality was difficult. In four years, only about 200 carats were produced, and much of that was reportedly sent to China. The old trade names—chlor-utahlite for the green material and sabalite for the yellow companion phosphate—belong to that early period when the stone was being tested in the jewelry world before mineral collectors fully understood the complexity of the nodules.
The most storied chapter began in 1936. Arthur Montgomery and Edwin Over had just been collecting epidote at Green Monster Mountain on Prince of Wales Island, Alaska, and they carried the name south to Utah. At Clay Canyon, “Ed did the digging, Art the marketing.” Together they gave the claim its enduring identity: the Little Green Monster. In the brief interval from 1937 to about 1940, Over mined several tons of material by hand. Montgomery, trained as a geologist and already alert to the scientific value of the nodules, made sure the best material did not simply vanish into lapidary stock. Major museums, especially Harvard and the Smithsonian, received important examples.
The nodules rewarded that care. Earlier mineralogical work had already shown the presence of unusual phosphates, but the Over-Montgomery mining opened better material, including superior crystals of several associated species and new unknowns for study. The mine was not a vast industrial operation; it was a classic specimen-mining venture in which careful eyes mattered as much as tonnage. By 1940, after several tons had been removed, new nodules became harder to find and the pair moved on.
The Smithsonian connection continued in a wonderfully practical way. In the 1950s, T. B. and Nellie Gillespie traveled to the Little Green Monster Mine, guided in part by the collecting world around Montgomery and Over. They found large variscite specimens and had them “sawed and polished” by the Smithsonian’s Mineral Department. The payment arrangement was old-school and elegant: the “fee for service was the other half of the nodules.” As a result, some Gillespie Museum variscites—and related specimens such as montgomeryite and overite—have twins in Washington, D.C.
Arthur Montgomery’s own life after Clay Canyon widened the locality’s historical reach. He operated the Harding mine in New Mexico during World War II, supplying tantalum, beryllium, and lithium for the war effort, and later helped preserve that mine as a teaching resource. He earned his PhD at Harvard in 1951, taught at Lafayette College, and helped establish both The Mineralogical Record and Friends of Mineralogy. The Little Green Monster story is therefore not just about green nodules in Utah; it sits in the same life arc that helped shape modern American mineral collecting and mineral preservation.
Ed Over’s story stayed closer to the field. He became one of the great commercial field collectors of the twentieth century, associated with exceptional minerals from the Red Cloud mine, the Topaz Mountains, Mt. Antero, Quartzsite, Pikes Peak, and other classic localities. He died in the field world he knew best, found in his car near the Lot mine in the remote Nine Mile Hill area of Colorado, where he had been collecting mineral specimens. For collectors who value provenance, an Over-associated Clay Canyon piece carries a direct link to that hard, specimen-hunting tradition.
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