Variscite and Associated Phosphates from Fairfield, Utah

Richard W. Thomssen
Dayton, Nevada

Introduction

Variscite from the Clay Canyon deposit near Fairfield, Utah was first identified in 1893. Its compact, microcrystalline nature and pleasing color in various shades of green led to early recognition of its use as a semi-precious gemstone. Mining and marketing of the variscite as "chlor-utahlite" on a small scale for the jewelry trade continue up to about the time of the World War 1. Associated with the variscite in nodular masses was a compact banded yellow material that soon found a market as "sabalite" though it was not nearly as popular as variscite. Some of the nodules are sufficiently altered that open pockets have developed. Occasionally crystals of a blue green mineral are to be found and these turned out to be a new mineral which was named "wardite" (Packard, 1896). Strangely, thirty-four years were to pass before another mineralogical paper concerning the unusual phosphate minerals of this deposit was to appear. Eight new minerals were then described and, ten years later, three additional new minerals were named. Subsequently, re-examination of these eleven new minerals led to five being discredited and an additional one was found to have been already described under another name. The remaining five have stood the test of re-examination and appear to be safely established. This is not to say that further work will not add to the sum of knowledge about these five and, perhaps, disclose the presence of additional new minerals.

Location and Geology
The Clay Canyon phosphate deposit is located in the southwest quarter of section 21, Township 6 South, Range 3 East in the southern Qquirrh Mountains in extreme western Utah County. This area lies some 50 miles southwest of Salt Lake City and it can be reached via State Highway 73 westerly from Lehi through Cedar Fort and Fairfield. The turnoff to the northwest to Clay Canyon is 1.5 miles west of Fairfield and it is approximately another 3 miles to the mine. The mine is covered by a patented mining claim, Little Green Monster, and is private property. Permission to collect should be acquired from the owner. This area of the Quirrh Mountains consits principally of sedimentary rocks of Paleozoic age. The mine is situated within the upper part of the Great Blue Limestone of Mississippian age. This formation actually contains sedimentary rocks other than limestone including beds of shale. The phosphate deposit lies on the crest of a small fold in the sediments which was shattered or brecciated during the process of folding (Gilluly, 1932). It was suggested by Larsen (1942c) that the phosphate nodules were deposited by ground water which derived its load of phosphate from weathering of the Phosphoria Formation. This Permian sedimentary rock was separated from the Great Blue Limestone by some 25,000 feet of intervening Mississippian, Pennsylvanian and Permian rocks (Welsh and James, 1961). It seems likely that ground water would have disbursed the phosphates derived from the Phosphoria rather than concentrate them while five miles of rock were eroding away. Another source for the phosphate must be sought and it is likely that it is within one of the shale beds in the Great Blue Limestone. The area around Clay Canyon has been subjected to extensive hydrothermal alteration, probably related to the intrusion of rhyolite plug located one mile north of the head of Clay Canyon (Jewell and Parry, 1987). The depositional scenario is one in which water heated by the rhyolite intrusion dissolved phosphates from a shale bed within the Great Blue Limestone, migrated upward toward the surface, no great distance away, and deposited variscite where it contacted colder waters in brecciated shaly limestone at the crest of the folded sediments. As the hot waters which deposited the variscite began to cool off, they changed in character and promoted the alteration and dissolution of the variscite, forming crandallite and a host of other hydrous alkali aluminum phosphates. Subsequent erosion then removed the overlying rocks exposing the deposit at the present surface. (go to top)

History

Variscite from the Clay Canyon deposit was first brought to the attention of the scientific world in December, 1893 by Mr. F. T. Millis of Lehi, Utah, who sent a specimen to Mr. Merrill, Curator of Geology in the U.S. National Museum (Smithsonian Institution). Mr. Millis related that the material occurred in the form of "nuggets" in a quartz vein near Lewiston (now Mercur), Utah, some twenty miles west of Lehi (Figure 1). This specimen was subjected to blowpipe examination, a useful technique which has unfortunately fallen into disuse, and found it to have the characteristics of "peganite". A chemical analysis of the specimen showed that its composition was the same as variscite and "peganite" has subsequently been considered to be a poorly analyzed variscite (Packard, 1894). At about the same time or slightly later, Mr. Don McGuire of Ogden, Utah discovered compact nodular variscite in Cedar Valley, near old Camp Floyd (first name for Mercur mining district), Utah (Kunz, 1894). This is certainly the same locality as that from which Mr. Millis obtained his material. Unfortunately, there is no record of the relationship of Millis and McGuire and we can only surmise who actually found the locality first. However, Don McGuire acquired the deposit and produced variscite for the jewelry trade from it for many years (Sterrett, 1908, 1914). Kunz suggested the name "utahlite" for the material and this name was shortly amended to "chlor-utahlite" Sterrett, 1909) in apparent reference to the materialÕs green color and, possibly to more easily promote the material to the jewelry trade. The specimen examined by Merrill and Packard at the National Museum was described as a large nodular mass, measuring nearly seven inches in its longest dimension. Green variscie in sections were separated from each other by banded envelopes of a yellow mineral, crandallite between which and the green is a powdery white coating (Packard, 1894). Subsequently, John M. Davison wrote that a considerable quantity of variscite had been received by WardÕs Natural Science Establishment of Rochester, New York. In the variscite nodules he found cavities left by the decomposition of the variscite. These were encrusted with light green to bluish green crystals of a new phosphate mineral, which he named wardite after Professor Henry A. Ward (Davison, 1896). Mineralogical examination of the variscite nodules and the various alteration minerals then ceased for 27 years when in 1923, Esper S. Larsen of Harvard University and Earl V. Shannon of the U. S. National Museum undertook an intensive study of the variscite nodules utilizing material in the collection of their respective institutions and a large collection loaned to them by George L. English at WardÕs Natural Science Establishment. In the summer of 1927, Larsen visited the locality and collected a few specimens from the dump.

Larsen found that the deposit had been developed by a short tunnel and drift. The results of Larsen and ShannonÕs work disclosed the presence of eight new minerals: dehrnite, deltaite, dennisonite (davisonite), englishite, gordonite, lehiite, lewistonite and millisite (Larsen and Shannon, 1930a). Only three (englishite, gordonite and millisite) of the original eight minerals have stood the test of further examination by mineralogists in the intervening 60 years and have not been discredited. In the fall of 1936, the Clay Canyon locality was visited by Arthur Montgomery and Edwin Over, fresh from their collecting trip to the classic epidote localities at the Jumbo mine and Green Monster Mountain on Prince of Wales Island, Alaska, and plans made to mine the deposit for both variscite and the rarer phosphate species. In the summer of 1937 and again in 1939 they managed to mine thousands of pounds of nodules which were distributed among major museums, especially Harvard and the Smithsonian Institution, collectors and mineral dealers. Far better crystals of several of the phosphates were found including gordonite and wardite and three unknowns. Frederick H. Pough, Curator of Minerals, American Museum of Natural History, acquired some of the gordonite crystals and characterized the crystal forms present, noting the resemblance as did Larsen and Shannon with the triclinic species paravauxite described by Samuel Gordon in 1923 (Pough, 1937b). Pough also found wardite crystals suitable for measurement on the optical goniometer and characterized the crystal forms for this species (Pought, 1937a). Duncan McConnell of the University of Minnesota demonstrated that both dehrnite and lewistonite were members of the apatite group. He suggested that dehrnite was a sodium member and that lewistonite was a potassium member on the basis of the analyses given in Larsen and ShannonÕs original 1930 paper (McConnell, 1938). In 1940 in one of a series of papers reporting on research done for his PhD. Dissertation on the Clay Canyon deposit, Esper S. Larsen, III, the son of Esper S. Larsen noted above, described two new phosphate minerals, overite and montgomeryite (Larsen, 1940a). Together with Arthur Montgomery, Larsen described sterrettite, unknowingly adding to a tale of error and confusion about which more will be forthcoming below (Larsen, 1940b). In 1942, Esper S. Larsen, III, published a general paper, which appeared in three parts, on the mineralogy of the varisicite nodules (Larsen, 1942a, 1942b and 1942c). He discussed the characteristics of some of the phosphate minerals and went into considerable detail about their sequence of formation from the precursor, variscite. Commencing in 1960 a series of papers by several investigators demonstrated that five of the species named and described by Larsen and Shannon were actually known species already described and well entrenched in the mineralogical literature. It was concluded that deltaite is a mixture of crandallite and hydroxylapatite (Elberty and Greenberg, 1960). Alice M. Blount of the University of Wisconsin studied the crystal structure of crandallite and concluded that "deltaite" is identical essentially, corroborating the conclusion of Elberty and Greenberg (Blount, 1974. Pete J. Dunn of the department of Mineral Sciences at the Smithsonian Institution examined in detail dehrnite and lewistonite. He concluded that both minerals were carbonate-fluorapatite with no sodium or potassium, respectively. The I.M.A. Commission on New Minerals and Mineral Names approved the discreditations (Dunn, 1978). Eight years later Pete Dunn and Carl A. Francis of Harvard Mineralogical Museum discredited both davisonite and lehiite. Davisonite was found to be a mixture of apatite and crandallite and lehiite is identical to crandallite. The I.M.A. Commission on New Minerals and Mineral Names has approved the discreditations (Dunn and Francis, 1986). (go to top)

Species

A brief review of some of the characteristics of each mineral will be given in the approximate order in which they are believed to have formed in the deposit.

Variscite This mineral, a hydrous aluminum phosphate, occurs in dense microcrystalline nodular masses; No crystals have been found at this location. The beautiful green color has been attributed to small quantities of vanadium (0.53%) and chromium (0.069%) substituting for phosphorus (Foster and Schaller, 1966). Significant amounts of scandium, 0.001-0.1%, have been found (Frondel, Ito and Montgomery, 1968). All other phosphates in the deposit are believed to have formed at the expense of variscite through the action of hydrothermal solutions.

Crandallite The first mineral to form from variscite through the addition of calcium, this yellow to light olive green species occurs in a variety of massive and crystal habits. The most abundant forms of this mineral cover the entire spectrum from massive, cherty material through yellowish and pinkish spherulitic cleavages to white, chalky crusts. When crystallized, this mineral varies from feathery clusters of fibrous needles through more substantial, but tiny prismatic crystals to distinct flattened rhombs with an equally developed base. The Clay Canyon material was first called pseudowavellite, however, the name crandallite had priority (Palache, Berman and Frondel, 1957). This mineral in its various modes has been shown to contain significant amounts of vanadium, 0.37%, and chromium 0.67% (Foster and Schaller, 1966); strontium, >1.0% (Foster and Schaller, 1966); and scandium, 0.01-0.80% (Frondel, Ito and Montgomery, 1968). The first two elements certainly are responsible for the color.

Goyazite The existence of this mineral was obscured for many years by its resemblance to and close association with crandallite. Its strontium content was the first clue to its existence in the deposit (Frondel, Ito and Montgomery, 1968; Blount, 1974). Although tiny crystals may be present, they are impossible to distinguish from crandallite without chemical or optical tests. (go to top)

Wardite The blue green to bluish grey component of the "eyes" or spherules and veining within variscite, this species also occurs in blue green to yellow crystals lining cavities in the more altered nodules (Packard, 1896; Montgomery, 1970a). (photograph and single crystal drawing) The blue green variety owes its color, no doubt, to minor amounts of vanadium and or chromium substituting for phosphorus as in the case of variscite. Solutions altering the variscite now have become enriched in sodium.

Concentric accretion of wardite and millisite.

Millisite White to clear component along with wardite of the spherules and veining noted above. No isolated crystals have been found of this species, which is similar in composition to wardite but containing calcium.

Gordonite This mineral occurs within open cavities generally near altering variscite as clusters of brilliant prismatic crystals. Crystals up to 7 mm have been reported, but they usually are in the millimeter range (Montgomery, 1970b). (photograph and single crystal drawing) Gordonite is usually colorless, but can be faintly yellow or a pleasing shade of pale violet. Here again we possibly are seeing the effects of one of the chromophores, vanadium and (or) chromium. Gordonite is the first species to appear in the deposition sequence containing magnesium and may be forming at the expense of crandallite.

Gordonite and Wardite
(photographs by Lou Perloff)

Montgomeryite The bright blue green bladed crystals of this mineral are the most distinctive of all the well-crystallized phosphates from the Clay Canyon deposit. Crystals are in the millimeter range and typically occur in cavities implanted upon crandallite and near variscite (Larsen, 1940). (photograph and single crystal drawing)

Montgomeryite
(photographs by Lou Perloff)

Overite The rarest of the phosphate minerals, clear pale yellow clusters of tiny orthorhombic crystals of this mineral are most distinctive. (photograph and single crystal drawing) As in the case of montgomeryite, this species occurs in cavities implanted on crandallite and near variscite. These two species, like gordonite contain magnesium and probably formed at the expense of crandallite. (Larsen, 1940) (go to top)

Overite on Crandallite
(photographs by Lou Perloff)

Englishite Similar to gordonite in its position within cavities close to variscite, this mineral can be readily identified by its grayish to colorless, bladed habit and, where broken, its prominent cleavage. Crystal aggregates range in size up to about 2 mm. (photograph) This is the only phosphate in which potassium is essential along with sodium and the ever-present calcium (Dunn, Rouse and Nelen, 1984, More, 1976)

Englishite on Variscite with Wardite
(photographs by Lou Perloff)

Kolbeckite This rare species was first described from Clay Canyon deposit under the name, sterrettite, as an aluminum phosphate (Larsen and Montgomery, 1940). The identity of "eggonite" from Altenberg Belgium with sterrettite was proposed while both were still considered aluminum phosphates (Bannister, 1941). Then in 1959, it was discovered that both sterrettite and kolbeckite were, in fact scandium phosphates (Mrose and Wappner, 1959). In 1980, the I.M.A. Commission on New Minerals and Mineral Names while accepting that all three minerals were identical, rejected the name sterrettite, and were almost equally divided over the name kolbeckite and eggonite. (Hey, Milton and Dwornik, 1982). Kolbeckite currently is accepted as the valid name for this hydrous scandium phosphate (Nickel and Nichols, 1991; Fleischer and Mandarino, 1991). Clear crystals of kolbeckite are generally tiny, measuring < 0.5 mm, although a few giants of 8 mm have been found. They are always on crandallite, which can be well crystallized, and are frequently associated with yellow wardite. (photograph and single crystal drawing) (go to top)

Kolbeckite with Crandallite
(photographs by Lou Perloff)

Carbonate-fluorapatite Among the last minerals to form, a large variety of hexagonal crystals of this species occur in cavities generally associated with crandallite and, occasionally, with other species (Dunn, 1980). With similar habit crystals occurring in nodule after nodule, a specific difference in composition may be responsible. Perhaps it lies in differences in relative amounts of carbonate and fluorine present. Further investigation is necessary to illuminate this matter. Still enriched in calcium and phosphate, the solutions precipitating carbonate-fluorapatite no longer contain aluminum (photographs)

Carbonate-fluorapatite on Crandallite (left) and on Wardite (right)
(photographs by Lou Perloff)

Additional species Alunite, calcite and quartz together with more or less argillic limestone comprise the matrix for the phosphate nodules. Alunite is cream to white in color and moderately to coarsely crystalline. It is fairly common in the brecciated, unweathered portions of the deposit. Quartz is the dominant component in the dark-colored cherty material that is so prevalent. Limonite pseudomorphs after pyrite occur on crandallite in highly weathered nodules. This is the only evidence of the presence of sulfides having occurred in the Clay Canyon deposit, although there is locally abundant limonite-staining of the altered portions of the deposit, it cannot definitely be attributed to the weathering of pyrite. (go to top)

References

Bannister, F. A. (1941) The identity of "eggonite"with sterrettite, Mineralogical Magazine, Volume 26, pages131-133.

Blount, Alice M. (1974) The crystal structure of crandallite, American Mineralogist, Volume 59, pages 41 to 47.

Davison, John M. (1896) Wardite: a new hydrous basic phosphate of alumina, American Journal of Science, Fourth Series, Volume 2, pages 154 to 155.

Dunn, Pete J. (1978) Dehrnite and lewistonite: discredited, Mineralogical Magazine, Volume 42, pages 282 to 284. Dunn, Pete J. (1980) Carbonate-fluorapatite from near Fairfield, Utah, Mineralogical Record, Volume 11, pages 33 to 34.

Dunn, Pete J. and Rouse, Roland C. and Nelen, Joseph A. (1984) Englishite: new chemical data and a second occurrence, from the Tip Top Pegmatite, Custer, South Dakota, Canadian Mineralogist, Volume 22, pages 469 to 470.

Dunn, Pete J. and Francis, Carl A. (1986) Davisonite and lehiite discredited, American Mineralogist, Volume 71, pages 1515 to 1516.

Elberty, W. T. and Greenberg, S. S. (1960) Deltaite is crandallite plus hydroxylapatite, Geological Society of America Bulletin, Volume 71, page 1857 (abstract).

Fleischer, Michael and Mandarino, Joseph (1991) Glossary of Mineral Species, Seventh Edition, Mineralogical Record, Tucson, Arizona.

Foster, Margaret D. and Schaller, Waldemar T. (1966) Cause of colors in wavellite from Dug Hill, Arkansas, American Mineralogist, Volume 51, pages 422 - 429.

Frondel, Clifford and Ito, Jun and Montgomery, Arthur (1968) Scandium content of some aluminum phosphates, American Mineralogist, Volume 53, pages 1223-1231.

Gilluly, James (1932) Geology and ore deposits of the Stockton and Fairfield Quadrangles, Utah, Professional Paper 173, U.S. Geological Survey, Washington, D.C.; 171 pages.

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Hey, Max H. and Milton, Charles and Dwornik, E.J. (1982) Eggonite (Kolbeckite, Sterrettite), ScPO4.2H20, Mineralogical Magazine, Volume 45, pages 493-497.

Jewell, Paul W. and Parry, W.T. (1987) Geology and hydrothermal alteration of the Mercur Gold Deposit, Utah, Economic Geology, Volume 82, pages 1958-1966.

Kunz, George F. (1984) Utahlite, U.S. Geological Survey 16th Annual Report, Part IV, page 602.

Larsen, Esper S. and Shannon, Earl V. (1930a) The minerals of the phosphate nodules from near Fairfield, Utah, American Mineralogist, Volume 15, pages 307-337.

Larsen, Esper S. and Shannon, Earl V. (1930b) Two Phosphates from Dehrn; Dehrnite and Crandallite, American Mineralogist, Volume 15, pages 303-306.

Larsen, Esper S., III (1940) Overite and Montgomeryite: Two new minerals from Fairfield, Utah, American Mineralogist, Volume 25, pages 315-326.

Larsen, Esper S., III (1942a) The mineralogy and paragenesis of the variscite nodules from near Fairfield, Utah, part 1, American Mineralogist, Volume 27, pages 281-300.

Larsen, Esper S., III (1942b) The mineralogy and paragenesis of the variscite nodules from near Fairfield, Utah, part 2, American Mineralogist, Volume 27, pages 350-372.

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Larsen, Esper S., and Montgomery, Arthur (1940) Sterrettite, a new mineral from Fairfield, Utah, American Mineralogist, Volume 25, pages 513-518.

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Modreski, Peter J. (1976) Little Green Monster Variscite mine, Mineralogical Record, Volume 7, pages 269-270. Montgomery, Arthur, (1970a) the phosphate minerals of Fairfield, Utah, Rocks and Minerals, Volume 45, Number 11, pages 667-674.

Montgomery, Arthur, (1970b) The phosphate minerals of Fairfield, Utah, part 2, Rocks and Minerals, Volume 45, Number 12, pages 739-745.

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Montgomery, Arthur, (1971b) The phosphate minerals of Fairfield, Utah, part 4, Rocks and Minerals, Volume 46, Number 2, pages 75-80.

Moore, Paul B. (1976) Derivative structures based on the alunite octahedral sheet: mitridatite and englishite, Mineralogical Magazine, Volume 40, pages 863-866.

Mrose, Mary E. and Wapner, Blanca (1959) New data on the hydrated scandium phosphate minerals: sterrettite, "eggonite", and kolbeckite, Geological Society of America Bulletin, volume 70, pages 1648-1649 (abstract).

Nickel, Ernest H. and Monte C. Nichols (1991) Minerals reference manual, Van Nostrand Reinhold, New York, 250 pages.

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Palache, Charles and Harry Berman and Clifford Frondel (1951) The system of mineralogy, Seventh Edition, Volume II, New York. Pough, Frederick H. (1937a) The morphology of wardite, American Museum Novitates, Number 932, 5 pages.

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