Variscite and Associated Phosphates from Fairfield,
Richard W. Thomssen
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.
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)
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.
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)
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)
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)
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
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)
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)
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