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) form- ing 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 go- dovikovite. 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.