Ammonium Sulfate Minerals from Mikasa, Hokkaido, Japan: Boussingaultite, Godovikovite, Efremovite and Tschermigite

158 Journal of MineralogicalN. Shimobayashi, and Petrological M. OhnishiSciences, and Volume H. Miura 106, page 158─ 163, 2011

LETTER

Ammonium sulfate minerals from Mikasa, Hokkaido, Japan: boussingaultite, godovikovite, efremovite and tschermigite

* ** *** Norimasa Shimobayashi , Masayuki Ohnishi and Hiroyuki Miura

*Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan ** 80-5-103 Misasagi Bessho-cho, Yamashina-ku, Kyoto 607-8417, Japan ***Department of National History Sciences, Graduate School of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo 060-0810, Japan

Four ammonium sulfate minerals, i.e., boussingaultite, godovikovite, efremovite and tschermigite, were found from coal gas escape fractures at Ikushunbetsu, Mikasa City, Hokkaido, Japan, on the field survey in 2009. The minerals were identified using XRD, SEM-EDS, XRF and/or CHN analyses. This is the first occurrence of these four mineral species in Japan. Godovikovite is the most common species in this survey and has Al/(Al + Fe3+) ~ 0.9. The mineral coexists with efremovite. These usually occur as very fine admixtures (<10 μm) forming porous crust up to several millimeters in thickness. Boussingaultite [Mg/(Mg + Fe) = 0.96 to 0.97] occurs as aggregates of platy crystals up to 1 mm in diameter and 0.2 mm in thickness or as very fine admixtures (<10 μm) with tschermigite forming porous stalactitic-like aggregate. Godovikovite, efremovite and boussingaultite were formed as a primary sublimate from coal-gas. Tschermigite is considered to be a hydration product of godovikovite.

Keywords: Godovikovite, Efremovite, Tschermigite, Boussingaultite, Ammonium sulfate, Ikushunbetsu, Mikasa

INTRODUCTION ties of the ammonium sulfate minerals obtained from Mi- kasa. A dozen of ammonium sulfate minerals were reported as sublimate from coal gas at burning coal-dumps (BCDs) OCCURRENCE AND SAMPLE DESCRIPTION as summarized by Parafiniuk and Kruszewski (2009);

- however, these NH4 bearing sulfate minerals have not The Ikushunbetsu area is located on the eastern side of the been found in Japan so far. Also in Japan, a small-scale Ishikari plain which has many large coal mines and is BCD ignited by natural causes has been known to exist at covered by the Ikushunbetsu coal-bearing formation of the left bank of Ponbetsu River in the Ikushunbetsu area, the Palaeogene period, which consists of altered sand- Mikasa, Hokkaido (141°58´E, 43°16´N). During a miner- stone and mudstone containing two or three coal seams. alogical investigation in this area, some sublimate miner- In this locality, sulfate minerals occur as efflorescence on als were collected on September 11, 2009. Powder X-ray the coal gas escape fractures, and are formed by sublimate diffraction (XRD) and chemical analyses indicate them to from the coal gas that has been in burning of underground be the ammonium sulfate minerals including boussin- coal layer. A new anhydrous ferric sulfate, mikasaite, 3+ gaultite [(NH4)2Mg(SO4)2∙6H2O], godovikovite [(NH4) (Fe ,Al)2(SO4)3, was discovered by Miura et al. (1994) 3+ (Al,Fe )(SO4)2], efremovite [(NH4)2Mg2(SO4)3] and ts- around the most active fracture of those times (in 1992). chermigite [(NH4)Al(SO4)2∙12H2O]. This is the first oc- Sulfur, sal ammoniac, alunogen, voltaite and hexahydrite currence of these four mineral species in Japan. The paper have been also found in this locality. deals with the mode of occurrence, mineralogical proper- The mineral samples for this study were collected doi:10.2465/jmps.101021f around the same fractures that mikasaite was detected in N. Shimobayashi, [email protected] Corresponding au- 1992. The present samples are roughly classified into thor three types: (A) aggregates or coatings of platy crystals Ammonium sulfate minerals from Mikasa 159 up to 1 mm in length and 0.2 mm in thickness on the al- Ni-filtered CuKα radiation generated at 40 kV and 30 mA. tered sandstone and mudstone (Fig. 1a), (B) botryoidal Unit cell parameters were calculated from the XRD data by aggregates, stalactitic-like nodules or coatings of white to the least squares using a CellCalc (Miura, 2003). light-brown color on the altered sandstone and mudstone Chemical analyses were carried out using a SEM- (Fig. 1b) and (C) a small stalactitic-like aggregate of yel- EDS (HITACHI S-3000H equipped with a HORIBA low to light-brown color (Fig. 1c). Type-B was the most EMAX-7000 EDS system) operating at 20 kV with a abundant around the gas escape fractures on the field sur- beam current of 0.3 nA. Polished thin sections, however, vey in 2009. Type-A samples were scattered near the cannot be prepared for the SEM-EDS analyses through small fractures whose gas escape was relatively weaker the usual procedure because the present ammonium sul- than the fractures where type-B aggregates were formed. fate minerals are water-soluble. As-grown surfaces of the Only one specimen of type-C was found in the dump crystals in the type-A samples (Fig. 1d) were barely used away from the fractures by a few meters. for the SEM-EDS analysis. Quantitative analyses were performed that the standard materials used were periclase

METHODS (MgO), hematite (Fe2O3), rhodonite (MnSiO3), and pent-

landite [(Fe,Ni)9S8]. The data were corrected by a ZAF Powder X-ray diffraction (XRD) patterns combined che method. However, most minerals in types-B and C sam- mical analyses by SEM-EDS and XRF were used to identi- ples occur as intimate mixtures, which makes quantitative fy mineral species in the present samples. The samples X- chemical analyses impossible to carry out. Chemical com- rayed were carefully separated under a stereomicroscope positions of the ammonium sulfate minerals contained in and then were gently ground to powder in an agate mortar. types-B and C samples could not be determined separate- XRD was performed with a RIGAKU SmartLab-SS using ly even by using SEM-EDS. Therefore, bulk composi-

Figure 1. Photographs of ammonium sulfate minerals from the Ikushunbetsu area, Mikasa. (a) Aggregate of platy boussingaultite crystals on the altered host rock. (b) Botryoidal aggregate of godovikovite in association with efremovite. (c) Stalactitic-like aggregate of tschermigite in association with boussingaultite. (d) Secondary electron image showing euhedral platy crystal of boussingaultite. (e) Back-scattered electron image showing fine admixture of godovikovite and efremovite forming porous crust. 160 N. Shimobayashi, M. Ohnishi and H. Miura

Table 1. XRD data for boussingaultite

1. Mikasa, Hokkaido, Japan (Present work). 2. Synthetic boussingaultite (ICDD-PDF 35-771).

tions of them were measured using an XRF method identified as an almost single phase of boussingaultite. (RIGAKU ZSX Primus II). Samples of type-B are identified with XRD as godoviko-

- Not only H2O but also (NH4)2O cannot be quantita- vite + efremovite ± hexahydrite, and type C as tscher- tively determined with EDS and XRF. The total nitrogen migite + boussingaultite, both of which are inevitably as- and hydrogen contents of some samples were analyzed sociated with quartz and feldspars of the host rocks. using a YANACO MT-6 CHN analyzer at the Laboratory Godovikovite and efremovite usually occur as very fine for Organic Elemental Microanalysis, Kyoto University. admixtures forming porous crust (Fig. 1e) up to several Fourier-transform infrared-absorption (FT-IR) spectrum millimeters in thickness on the host rocks. was obtained with a JASCO MFT-680 FT-IR spectrome- ter (KBr pellet method). Boussingaultite

DESCRIPTION OF MINERALS The boussingaultite from Mikasa shows the two different modes of occurrence. One occurs as aggregates of hexag- Crystalline materials in the type-A samples (Fig. 1d) are onal platy crystals up to 1 mm in diameter and 0.2 mm in Ammonium sulfate minerals from Mikasa 161

Table 2. Representative XRD data for godovikovite + efremovite Table 3. Chemical analysis of godovikovite + efremovite

* Total Fe as Fe2O3. a) measured by XRF. b) estimated from CHN analysis. The total percent is normarized as 100.0 wt%.

∑1.03(SO4)2.00·5.97H2O. The formula closely corresponds to

the ideal formula of boussingaultite, (NH4)2Mg(SO4)2·

6H2O. The Mg/(Mg + Fe) ratio is 0.96 to 0.97.

Godovikovite + Efremovite 1. Mikasa, Hokkaido, Japan (Present work). 2. Godovikovite from Kopeysk, Chelyabinsk coal basin, Southern Representative XRD data of a type-B aggregate are listed Urals, USSR (ICDD-PDF 23-1). in Table 2 and compared with ICDD-PDF 23-1 (go- 3. Efremovite from Kladno, Czechoslovakia (ICDD-PDF 42- - 1432). dovikovite) and 42 1432 (efremovite). The unit cell pa- * Quartz. rameters are a = 4.764(5) Å, c = 8.284(8) Å, V = 162.8(3) Å3, and Z = 1 for the hexagonal cell of godovikovite and a = 10.034(4) Å, V = 1010.2(7) Å3, and Z = 4 for the cu- thickness on the host rock (type-A), and the other as very bic cell of efremovite, respectively. fine admixtures (< 10 μm) with tschermigite forming po- In combination with XRF and CHN analyses, the rous crust (type-C), and the properties of boussingaultite chemical composition of the admixture of godovikovite + of type-C could not be determined. Therefore, the former efremovite is quantitatively determined by normalizing as type of boussingaultite is described below. total 100.0 wt% (Table 3). EDS spectra show that the go- Boussingaultite crystals are white to colorless, and dovikovite contains Al, S and minor Fe, and does not con- the luster is dull or vitreous. The mineral has a perfect tain Mg and Mn; whereas efremovite contains Mg, S and cleavage in one direction. The XRD data (Table 1) were minor Mn, and does not contain Al and Fe. EDS spectra in good agreement with a synthetic compound (ICDD- also show that both minerals contain minor K. Assuming PDF 35-771), and the refined unit cell parameters are a = that Mg and Mn are contained only in efremovite and Al

9.323(3), b = 12.594(4), c = 6.215(4) Å, β = 107.04(4)°, V and Fe in godovikovite, and that H2O (3.9 wt%) is regard- 3 = 697.7(5) Å , and Z = 2. FT-IR spectrum shows the vi- ed as adsorbed water and can be ignored, we can deter-

- - −1 - - brations of O H and N H stretching (3373 cm ), H O H mine the empirical formula, [(NH4)1.1K<0.1]Σ1.1(Al0.9 −1 −1 3+ bending (1631 cm ), NH4 bending (1436 cm ), ν1 and ν3 Fe0.1)Σ1.0(SO4)2 for godovikovite, and [(NH4)2.0K<0.1]Σ2.0 −1 −1 SO4 stretching (1147 cm and 1091 cm ), and ν4 SO4 (Mg1.8Mn0.2)Σ2.0(SO4)3 for efremovite, respectively. The bending (627 cm−1), respectively. Chemical analyses com- Al/(Al + Fe3+) ratio of the godovikovite from Mikasa is bined with SEM-EDS and CHN gave MgO 10.90, FeO about 0.9.

0.72, MnO 0.20, (NH4)2O 14.09, SO3 44.32 and H2O 29.77, by normalizing as total 100.00 wt%. The empirical formula on the basis of S = 2 is (NH4)1.95(Mg0.98Fe0.04Mn0.01) 162 N. Shimobayashi, M. Ohnishi and H. Miura

Table 4. XRD data for tschermigite Tschermigite

Tschermigite was detected from only one specimen of Type-C in association with boussingaultite. The specimen as assemblage of tschermigite + boussingaultite is yellow to light brown color with vitreous luster. The XRD data of the tschermigite (Table 4) correspond to those of a synthetic compound (ICDD-PDF 83-1933), and the refined unit cell parameters are a = 12.2465(9) Å, V = 1836.7(2) 3 Å , and Z = 4. SEM-EDS analysis revealed that the mineral consists of Al and S, with small amounts of Fe. Bulk composition determined with XRF analysis for the tschermigite + boussingaultite assemblage reveals the atomic ratio of Al : Mg : Fe : S = 0.72 : 0.23 : 0.06 : 2.00. Assum- ing that Fe behaves as a trivalent cation and is contained predominantly in tschermigite, the Al/(Al + Fe3+) ratio of the tschermigite from Mikasa is about 0.9.

DISCUSSION

Godovikovite was first discovered in 1988 from BCD of the Chelyabinsk Coal Basin, Southern Urals, Russia (Jam- bor and Grew, 1990); efremovite was discovered from the same BCD in 1989 (Jambor and Grew, 1991). According to Jambor and Grew (1990), godovikovite is a primary component of sulfate crust, formed by the reaction of dump material with sulfuric acid. Parafiniuk and Krusze- wski (2009), who examined ammonium minerals from BCD of the Upper Silesian Coal Basin, Poland, suggested that hydration of primarily anhydrous sulfates, such as godovikovite → tschermigite, occurs in the outer part of the sulfate crust. In contrast, through the study of mineralization processes in Wuda coal-fire gas vents of Inner Mongolia, Stracher et al. (2005) suggested as one possi- bility, that gaseous N and S compounds together with water vapor reacted with Al-bearing minerals in the host rock (e.g., feldspar), and produced tschermigite primarily. The field survey in 2009, the ammonium-bearing anhydrous sulfate minerals such as godovikovite in association with efremovite are the most abundant mineral assemblage instead of mikasaite, around the active coal gas escape fractures. Miura et al. (1994) reported that mikasaite was formed as sublimate around the most active coal-gas escape fracture where the gas temperature reached a maximum of 307 °C. Miura (personal commu- nication, 2009), who conducted this field survey, attested 1. Mikasa, Hokkaido, Japan (Present work). that the gas escape in 1992, when mikasaite was found 2. Synthetic tschermigite (ICDD-PDF 83-1933). * around the same fracture, had been much more active Abbreviations and ICDD-PDF number: Bsg, boussingaultite (35- 771). than that in 2009. Hence, the gas temperature in 2009 + Mark means the peak overlapping that of tschermigite. should be supposed to be considerably lower than about 300 °C. Parafiniuk and Kruszewski (2009) described that efremovite is thought to be formed by the decomposition Ammonium sulfate minerals from Mikasa 163

- of dolomitic rocks by sulfuric acid and coal derived NH3 ACKNOWLEDGMENTS in the temperature range of 180-400 °C. Therefore, the present assemblage of godovikovite + efremovite should We are grateful to two anonymous referees and Dr. H. have been primarily formed from the coal-gas at about Okudera, an associate editor, for their constructive and 200-250 °C. The tschermigite + boussingaultite assem- critical reviews and editorial comments, respectively. blage observed in the type-C sample, collected away from the fracture, is regarded as hydration product of the go- REFERENCE dovikovite + efremovite assemblage. However, a presence of euhedral boussingaultite crystals in the type-A sample Jambor, J.L. and Grew E.S. (1990) New mineral names. American strongly suggests that all the boussingaultite are not nec- Mineralogist, 75, 240-246. Jambor, J.L. and Grew E.S. (1991) New mineral names. American essarily formed by the hydration of efremovite in the Mineralogist, 76, 299-305. same way. The euhedral platy shape of the boussingaultite Miura, H., Niida, K. and Hirama, T. (1994) Mikasaite, (Fe3+, is not thought to be transformed from cubic efremovite. It Al)2(SO4)3, a new ferric sulphate mineral from Mikasa city, is likely that the crystalline boussingaultite formed as a Hokkaido, Japan. Mineralogical Magazine, 58, 649-653. Miura, H. (2003) CellCal: A unit cell parameter refinement pro- primary sublimate from the coal-gas. TG-DTA curves of gram on Windows computer. Journal of the Crystallographic the boussingaultite crystals show an endothermic peak Society of Japan, 45, 145-147 (in Japanese). with weight loss at around 100 °C due to dehydration. Parafiniuk, J. and Kruszewski, Ł. (2009) Ammonium minerals The aggregates of the boussingaultite crystals were col- from burning coal-dumps of the Upper Silesian Coal Basin lected near the small fractures whose gas escape was rela- (Poland). Geological Quarterly, 53, 341-356. tively inactive. Taking the mode of occurrence into con- Stracher, G.B., Prakash, A., Schroeder, P., McCormack, J., Zhang, X., Van Dijk, P. and Blake, D. (2005) New mineral occur- sideration, it is suggested that the aggregates of the rences and mineralization processes: Wuda coal-fire gas boussingaultite crystals were formed directly from the vents of Inner Mongolia. American Mineralogist, 90, 1729- coal-gas at lower temperature than the assemblage of go- 1739. dovikovite and efremovite was produced. Manuscript received October 21, 2010 Manuscript accepted January 20, 2011 Published online March 29, 2011 Manuscript handled by Hiroki Okudera