Ramsbeckite from the Hirao Mine at Minoo, Osaka, Japan
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Journal of MineralogicalRamsbeckite and Petrological from the Hirao Sciences, mine Volumeat Minoo 99, page 19─24, 2004 19 Ramsbeckite from the Hirao mine at Minoo, Osaka, Japan * ** *** Masayuki OHNISHI , Shoichi KOBAYASHI , Isao KUSACHI , **** ***** Junji YAMAKAWA and Masao SHIRAKAMI *Department of Chemistry and Bioscience, College of Science and Industrial Technology, Kurashiki University of Science and the Arts, Kurashiki 712－8505, Japan **Division of Earth Sciences, Kurashiki University of Science and the Arts,Kurashiki 712－8505, Japan ***Department of Earth Sciences, Faculty of Education, Okayama University,Okayama 700－8530, Japan ****Department of Earth Science, Faculty of Science, Okayama University,Okayama 700－8530, Japan ****28－19 Zempoji－cho, Amagasaki, Hyogo 661－0973, Japan Ramsbeckite was found as a vein forming mineral in altered shale at the Hirao mine, Minoo, Osaka, Japan. It occurred as aggregates of euhedral granular crystals up to 0.5 mm across, in association with sphalerite, chalcopyrite, smithsonite, aurichalcite, amorphous manganese dioxide, schulenbergite, brochantite, serpierite, limonite and an unidentified mineral. It was emerald green to blue－green in color with a vitreous luster in hand specimen. An EPMA and CHNS/O analyzer gave the empirical formula (Cu9.380Zn5.542Ni0.034Co0.027Fe0.020 Mn0.013)∑15.016[(SO4)3.871(CO3)0.166]∑4.037(OH)21.958･6.06H2O on the basis of O = 44. The unit cell parameters were a = 16.106 (3), b = 15.568 (2), c = 7.109 (1) Å, β = 90.23 (1)°, and Z = 2. The mineral was optically biaxial negative with refractive indices α = 1.676, β = 1.704 and γ = 1.707, and 2VX(calc) = 37.8°. The Vickers micro- hardness was 162 (144－182) kg/mm2 (10 g load), and the Mohs hardness was 3.5. The measured density was 3.36 g/cm3. It is likely that ramsbeckite at the Hirao mine crystallized from Cu and Zn－bearing fluids. Introduction Its occurrence was described by Ohnishi et al. (2001), and this was the first report of the mineral in Japan. The Ramsbeckite, a copper zinc sulfate hydroxide hydrate, present paper deals with the detailed mode of occurrence was first described at the Bastenberg mine near Rams- and full mineralogical properties of ramsbeckite from the beck, and four other localities (the Glücksrad mine, the Hirao mine. Friedrichssegen mine, the Marie mine, and Ochsenhütte) in Germany by Hodenberg et al. (1985), who proposed Occurrence the ideal chemical formula (Cu, Zn)7(SO4)2(OH)10 ･ 5H2O. The mineral was also found at the Ecton mine, Pennsyl- The Hirao mine is developed in shale belonging to the vania, USA (Peacor et al., 1987), the La Veneziana mine, Tamba zone of the Jurassic age at Minoo city, and located Italy (Orlandi and Perchiazzi, 1989), the Waterbank, about 17 km north of Osaka city. The host rock has been Dylife and Brynarian mines, UK (Rust, 1992), the greatly hydrothermally altered to chlorite. The ore and Penrhiw mine, UK (Mason and Green, 1995), and gangue minerals found in the gallery have been summa- Monte Cengio (Saccardo et al., 2002). The crystal rized by Ohnishi et al. (2001; 2002). Among the miner- structure of ramsbeckite was determined by Effenberger als, sphalerite is the most predominant mineral, and this (1988), who proposed a revised chemical formula (Cu, disseminates through the altered shale. Zn)15(SO4)4(OH)22･6H2O. Ramsbeckite occurs in a veinlet cutting into the In February 1941, an emerald green mineral resem- altered shale as aggregates of euhedral granular crystals bling brochantite was collected by one of the authors up to 0.5 mm across. A SEM image of aggregates of the (M. S.) from the Hirao mine, Minoo, Osaka, Japan. euhedral crystals is shown in Figure 1. The veinlet has Recently, an analysis of the mineral using an X－ray dif- a width of approximately 0.5 mm. Smithsonite occurs fractometer and an EPMA revealed it to be ramsbeckite. on the veinlet wall, and ramsbeckite crystallizes in the center of the veinlet, as shown in Figure 2. Sphalerite, S. Kobayashi, [email protected] Corresponding author chalcopyrite, aurichalcite, amorphous manganese dioxide, I. Kusachi, [email protected]－u.ac.jp schulenbergite, brochantite, serpierite, limonite and an un- 20 M. Ohnishi, S. Kobayashi, I. Kusachi, J. Yamakawa and M. Shirakami Ramsbeckite from the Hirao mine at Minoo 21 Figure 1. SEM image of euhedral ramsbeckite crystals from the Figure 2. Photomicrograph of ramsbeckite from the Hirao mine. Hirao mine. Open －polarized light. Abbreviations: Ram, ramsbeckite; Smi, smithsonite; Sp, sphalerite; Ccp, chalcopyrite; Chl, chlorite. identified copper zinc sulfate mineral occur in the vicinity 3 of the veinlet. by heavy liquids is 3.36 g/cm , and the calculated density is 3.41 g/cm3. The Vickers microhardness is 162 (144 － 2 Physical and optical properties 182) kg/mm (10 g load), and the Mohs hardness is 3.5. These properties are compared with those of Hodenberg Ramsbeckite from the Hirao mine is emerald green to et al., Peacor et al., and Orlandi and Perchiazzi (1989) in blue－green in color with a vitreous luster in hand speci- Table 1. men, and it appears pale green in thin section. The min- The infrared absorption spectrum of ramsbeckite was eral exhibits a perfect {001} cleavage in the same manner measured by a KBr matrix method for the region 4000 to as that reported by Peacor et al. (1987), but in contrast to 250 cm−1, as shown in Figure 3. The strong absorption Hodenberg et al. (1985), who reported that ramsbeckite band at 3425 cm−1 is attributed to the OH stretching vibra- has no distinct cleavage. Optically, the mineral is biaxial tion, and the weak band at 1630 cm−1 to the OH bending negative with refractive indices α = 1.676, β = 1.704 and vibration. Several absorption bands in the region 1000 −1 γ = 1.707, and 2VX(calc) = 37.8°. The density measured to 1200 cm and numerous low frequency bands are Table 1. Physical and optical properties of ramsbeckite 1. Hirao mine, Minoo, Osaka, Japan. The present work. 2. Bastenberg mine, Germany (Hodenberg et al., 1985). 3. Ecton mine, Pennsylvania, USA (Peacor et al., 1987). 4. La Veneziana mine, Italy (Orlandi and Perchiazzi, 1989). 20 M. Ohnishi, S. Kobayashi, I. Kusachi, J. Yamakawa and M. Shirakami Ramsbeckite from the Hirao mine at Minoo 21 Figure 3. Infrared absorption spectrum of ramsbeckite from the Hirao mine. attributed to the vibrations of [SO4] tetrahedra and Table 2. Chemical compositions of ramsbeckite [(Cu, Zn) O6] octahedra, respectively. Chemical composition The chemical composition of ramsbeckite from the Hirao mine was obtained using an electron microprobe analyzer (JEOL JSM －5410LV + JED －2140). The accelerating voltage was 15 kV, the beam current was 0.15 nA, and areas of approximately 5 × 5 µm were scanned for 100 seconds. The concentration of CO2 was determined by a Parkin －Elmer 2400II CHNS/O analyzer using a sample picked under a binocular microscope. The H2O content was obtained by subtraction. The averaged results of three points are given in Table 2, and compared with those reported by Hodenberg et al. (1985), Peacor et al. (1987) and Orlandi and Perchiazzi (1989). The empirical formula is (Cu9.380Zn5.542Ni0.034Co0.027Fe0.020Mn0.013)∑15.016[(SO4)3.871 (CO3)0.166]∑4.037 (OH)21.958･6.06H2O on the basis of O = 44. Although ramsbeckite from the Hirao mine contains small amounts of Mn, Co, Ni, Fe and CO2, the formula is consistent with the ideal formula (Cu, Zn)15(SO4)4(OH)22･6H2O proposed by Effenberger (1988). The Zn / (Cu + Zn) value ranges from 0.346 to 0.393, which shows that the Zn content from this sample is richer than that from other localities. The mineral was easily soluble in dilute hydrochloric acid, but insoluble in ammonia water. 1. Hirao mine, Minoo, Osaka, Japan. The present work. 2. Bastenberg mine, Germany (Hodenberg et al., 1985). 3. Ecton mine, Pennsylvania, USA (Peacor et al., 1987). 4. La Veneziana mine, Italy (Orlandi and Perchiazzi, 1989). * by difference. 22 M. Ohnishi, S. Kobayashi, I. Kusachi, J. Yamakawa and M. Shirakami Ramsbeckite from the Hirao mine at Minoo 23 Table 3. X－ray powder diffraction 22 M. Ohnishi, S. Kobayashi, I. Kusachi, J. Yamakawa and M. Shirakami Ramsbeckite from the Hirao mine at Minoo 23 data for ramsbeckite 1. Hirao mine, Minoo, Osaka, Japan. The present work. 2. Bastenberg mine, Germany (Hodenberg et al., 1985). X－ray study only in a veinlet cutting into the altered shale. Smithonite occurs on the veinlet wall, and ramsbeckite is crystallized The X－ray powder diffraction data for ramsbeckite from in the center of the veinlet. The occurrence suggests that the Hirao mine was obtained using an X－ray diffractom- the smithonite crystallized first, and ramsbeckite was eter (Rigaku RINT 2500V) with graphite－monochroma- formed from the Cu and Zn －bearing fluids at the later tized CuKα 1 radiation generated at 40 kV and 120 mA. stage. From the minerals coexisting with ramsbeckite, The unit cell parameters calculated from the powder data the fluids are considered to originate from sphalerite and are a = 16.106 (3), b = 15.568 (2), c = 7.109 (1) Å, β = chalcopyrite. The mode of occurrence is similar to that 90.23 (1)°, and Z = 2. The data are shown in Table 3, of the Penrhiw mine, UK (Mason and Green, 1995). At and compared with those of the type specimen obtained the Penrhiw mine, ramsbeckite occurs in cavities and using a Guinier camera method by Hodenberg et al. veinlets in the siltstone and sphalerite blocks. However, (1985). The cell parameters are also consistent with the the mode of occurrence of ramsbeckite from the Hirao cell parameters (a = 16.088, b = 15.576, c = 7.102 Å and mine differs from that of the type specimen at the β = 90.22°) reported by Effenberger (1988), which were Bastenberg mine (Hodenberg et al., 1985), and that at the derived from 2θ values of 75 reflections of the type speci- Ecton mine (Peacor et al., 1987).