Introduction

The presence of Munakataite, a rare mineral species with the formula, Pb₂Cu₂(Se²⁺O₃)(SO₄)(OH)₄, was confirmed in November 2008 on a specimen from the Mammoth-Saint Anthony Mine, Tiger, Pinal Co., Arizona. The Munakataite occurs sparsely on a single thumbnail-sized specimen from Tiger as medium powder-blue acicular crystals, averaging 0.5 mm in length, and possessing a silky to adamantine luster. The crystals occur intimately associated with altered crystals of Boleite and two generations of Leadhillite crystals. Other associates on the same specimen include a third generation of Leadhillite crystals, Quartz, Cerussite, Djurleite, Covellite, and a number of unidentified, or inadequately identified, species, including a bladed microscopic lead sulfate silicate, with small percentages of zinc and copper—possibly a copper-bearing Queitite. The identification was made on the basis of compositional analysis using energy-dispersive X-ray spectroscopy (EDS), augmented with semi-quantitative wavelength-dispersive X-ray spectroscopy (WDS) for sulfur, and because the sample is consistent with the form and appearance of the species as set forth in the published description of Munakataite in 2008.

This discovery is significant because it is only the third reported occurrence of Munakataite, it is the first report of the species to be made subsequent to the original published description, and it is the first reported occurrence of the species on a specimen from outside of Japan. In addition, this is the first reported instance of a selenium-containing species from the famous Mammoth-Saint Anthony Mine. The specimen is in the collection of the author.

Background

The subject specimen, shown in figure 1, was purchased by Robert Meyer, the author of this report, on September 23, 1983 from the Mineralogical Research Company while attending the Pacific Northwest Friends of Mineralogy annual symposium, held that year in Tacoma, Washington, USA. On the macro level, the specimen is a small, (2.7 cm across), very nice example, consisting of pale blue Leadhillite crystals associated with Boleite. Sharon Cisneros, of the Mineralogical Research Company, told the author at the time of purchase that the subject specimen, and a similar companion piece, had come through trade from the Sorbonne mineral collection. The author made the attempt after the symposium to obtain the companion piece, but it could not be located, and Ms. Cisneros surmised that the specimen must have already been sold.

It is upon examination of the specimen with a stereoscopic microscope that some inkling of its true nature is revealed. On the micro level, the specimen exhibits a complex association of mineral species, some of which occur in more than one generation of crystallization, or that possess varying degrees of alteration. The intricate mineralogy of the specimen kindled an interest in the author, which led to years of study, and a number of analysis sessions in an attempt to fathom the piece’s mysteries.


Students of the mineralogy of the Mammoth-Saint Anthony Mine are likely to be familiar with the anomalous oxidized sequence of minerals proposed by Richard A. Bideaux in his 1980 Mineralogical Record article. Mineral species assigned to this anomalous sequence often have complex formulas involving more than one metallic element, and the group is characterized an abundance of halogen elements. Bideaux theorized that the anomalous sequence minerals formed in a “closed system,” a sort of pressure cooker of volatile elements that would disperse in a normal geochemical environments, but were constrained at Tiger, resulting in the formation of these unusual species and associations (1980).

A careful microscopic examination, performed by the author, of approximately one-hundred specimens from the anomalous sequence supports the notion of a closed system. Pods, seams, and zones of anomalous oxidized sequence species are often surrounded by a compact rind primarily consisting of Chrysocolla and Wherryite. The rind is often, in turn, surrounded by tough, highly siliceous wall rock. The pods within these impermeable layers exhibit complex mineralogical paragenesis suggestive of a reactive, enclosed environment.

While specimens from this anomalous group are typically complex, and often are surrounded by the rinds of siliceous rock, there is a considerable variety of different mineral assemblages represented. A given species, or variety, might occur in one assemblage and not another. Patterns among these associations were noted by Bideaux, and efforts to further categorize them are underway at the present by a Tiger Mineral Study Group consisting of Tiger mineral enthusiasts, which includes the author. One of the purposes of this report is to document such parageneses from Tiger.

Munakatite

The author noted some tiny powder-blue fibrous crystals on the subject specimen, (see figure 2), occurring on, and possibly formed at the expense of, altered crystals of Boleite. The fibrous crystals exhibited a silky luster, and closely resembled Cyanotrichite or possibly Connellite, but the association, and possible alteration from Boleite was intriguing. A analysis session using SEM-WDS was performed at Cannon Microprobe facilities in Seattle, Washington in May 1993. A composition consistent with Mammothite was revealed. The Mammoth-Saint Anthony Mine is the co-type locality for Mammothite, and the species was named for the Mammoth Vein and the town of Mammoth, which is near the mine (Peacor, 1985). However, the acicular pale blue crystals are not typical of the habit of Mammothite from Tiger (Peacor, 1985). Ironically, though, the Mammothite from the co-type locality of Laurium, Greece does occur in acicular crystals that closely resembled the unidentified species (Peacor, 1985). The asumption was that the fibrous crystals on the subject specimen comprised a new form of Mammothite from the Mammoth-Saint Anthony Mine, but consistent with the form the species takes at Laurium.


Years later, in October 2008, efforts were undertaken to further understand the paragenesis of the subject specimen, and some additional crystals of the fibrous species were analyzed using SEM-EDS, again at Cannon Microprobe. Surprisingly, the newly analyzed material was clearly not Mammothite, indeed, it was a lead-copper selenate—a much different composition!

The notes and sample block from the 1993 analysis session were examined in a effort to understand the disparity between the results. In the 1993 analysis, grains were removed from the specimen, were embedded in plastic, and the surface was polished to present a smooth surface that would be perpendicular to the electron beam of the instrument. Grains from numerous specimens were on the same sample block. A recent examination of the sample block from 1993 revealed that the fibrous material was not actually exposed in the polishing process, and that the “Mammothite” result must have come from an adjacent grain. The notes from that session were inconclusive, and the problem remains as to which specimen the Mammothite actually came from. Thus, this disparity between analyses was explained, much to the chagrin of the author.

The EDS spectrum of the unknown is shown in figure 3. A search by chemistry using Mindat’s utility revealed only two matches for composition, color, and form—Munakataite and Schmiederite. Both species are monoclinic; both are members of the Linarite-Chenite group (Ralph, 2009).
An SEM photograph of the unknown is shown in figure 4, and clearly exhibits consistent with a monoclinic mineral species.




Munakataite and Schmiederite are very closely related in terms of chemical composition as well. Schmiederite is a basic lead copper selenite selenate, while Munakataite is a basic lead copper selenite sulfate (Matsubara, 2008). Doing the simple stoichiometric calculation, an ideal example of Munakataite should have 4.7 percent sulfur, and an ideal Schmiederite should have no sulfur.

The type locale for Munakataite is the Munakata, Fukuoka, Prefecture, Kyushu Island, Japan, and it gets it’s name from Munakata City, the town where the mine is located (Matsubara, 2008). The article describing Munakataite also listed a second locality for the species, the Akita Prefecture, Tohuko Region, Honshu Island, Japan (Matsubara, 2008). The Kisamori Mine is known for large crystals of Linarite (Sadanaga, 1974), a trait it shares with the Mammoth Saint Anthony Mine (Bideaux, 1980).

The detection of sulfur in substances with abundant lead is problematic when using EDS analysis alone, because the sulfur peaks are masked by the peaks for lead. Thus, a follow-up analysis session had to be scheduled using WDS for the purpose of determining whether sulfur was present in the unknown. The follow-up session occurred on November 28, 2008, again at Cannon Microprobe facilities in Seattle, Washington, USA. Using pyrite as a standard for sulfur, the unknown was shown to have between 4 and 5 percent sulfur using semi-quantitative WDS analysis. Thus, the percentage of sulfur detected in the unknown is consistent with Munakataite, and the unknown is not Schmiederite.

The authors of the description of Munakataite in 2008 relied on the use of FT-IR analysis to determine that the species is a selenite-sulfate (Matsubara, 2008). The minute amount of material on the subject specimen, as well as the lack of an accessible FT-IR micro analyzer makes a confirmation of the subject material using FR-IR analysis from the Mammoth Saint Anthony Mine impractical. While FT-IR analysis is the most valid means of distinguishing Munakataite and Schmiederite, the percentage of sulfur detected using WDS and the form and color of the unknown make it reasonable to assert that the material is a true Munakataite (Matsubara, 2009).

References

Bideaux, R. A. (1980). Famous mineral localities: Tiger, Arizona. The mineralogical record, 11(3), 155-181.

Peacor, D. R., Dunn, P. J., Schnorrer-Köhler, G., & Bideaux, R. A. (1985). Mammothite, a new mineral from Tiger, Arizona and Laurium, Greece. The mineralogical record, 16(2), 117-120.

Ralph, J (webmaster). (2009). Mindat.org - the mineral and locality database. Retrieved February 14, 2009, from http://www.mindat.org/.

Matsubara, S., Mouri, T., Miyawaki, R., Yokoyama, K., & Nakahara, M. (2008). Munakataite, a new mineral from the Kato Mine, Fukuoka, Japan. Journal of Mineralogical and Petrological Sciences, 103, 327-332. Retrieved February 14, 2009, from http://www.jstage.jst.go.jp/article/jmps/103/5/327/_pdf. [Link Broken? Jun 2013]

Matsubara, S. (2009). Personal communication (e-mail). February 18, 2009.

Sadanaga, R, and Bunno, M. (1974). The Wakabayashi Mineral Collection. Bulletin No. 7. The University Museum, University of Tokyo. http://www.um.u-tokyo.ac.jp/publish_db/Bulletin/no07/no07000.html

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