Journal of MineralogicalMiyahisaite, and Petrological a new mineral Sciences, of the hedyphane Volume 107, group page 121─ 126, 2012 121

Miyahisaite, (Sr,Ca)2Ba3(PO4)3F, a new mineral of the hedyphane group in the supergroup from the Shimoharai mine, Oita Prefecture, Japan

* ** ** Daisuke Nishio-Hamane , Yukikazu Ogoshi and Tetsuo Minakawa

* The Institute for Solid State Physics, the University of Tokyo, Kashiwa 277-8581, Japan **Departments of Earth Science, Faculty of Science, Ehime University, Matsuyama 790-8577, Japan

Miyahisaite, (Sr,Ca)2Ba3(PO4)3F, a new mineral of the hedyphane group in the apatite supergroup, is found in the Shimoharai mine, Oita Prefecture, Japan. Miyahisaite is colorless and occurs as a pseudomorphic aggregate (up to about 100 μm in size) along with in the matrix in a namansilite-rich layer of the chert. Its hardness is 5 on the Mohs scale, and its calculated density is 4.511 g/cm3. The empirical formula of miyahi-

saite is (Sr1.366Ca0.717)Σ2.083Ba2.911P3.002O12(F0.898OH0.088Cl0.014)Σ1.00, which is representatively shown as (Sr,Ca)2

Ba3(PO4)3F. Its simplified ideal formula is written as Sr2Ba3(PO4)3F, which requires 23.25 wt% SrO, 51.62 wt%

BaO, 23.89 wt% P2O5, 2.13 wt% F, and −0.90 wt% F = O, for a total of 100.00 wt%. The mineral is hexagonal 3 with a space group P63/m, unit cell parameters a = 9.921 (2) Å, c = 7.469 (3) Å, and V = 636.7 (3) Å , and Z = 2.

The eight strongest lines in the powder XRD pattern [d (Å), (I/I0), hkl] are 3.427 (16) 102, 3.248 (22) 120, 2.981 (100) 121, 2.865 (21) 300, 1.976 (23) 123, 1.874 (16) 140, 1.870 (15) 004, and 1.864 (17) 402. The mineral was formed by the reaction between fluorapatite and the Ba-bearing fluid that produced the aegirine-rich layer with hydrous Ba-rich minerals during the late-stage activity.

Keywords: Miyahisaite, New mineral, Hedyphane group, Apatite supergroup, Shimoharai mine

INTRODUCTION mine, Oita Prefecture, Japan. Considering the allocation of ions to different sites in apatite supergroup minerals, Apatite supergroup minerals are found in many geological this mineral is understood to be a new member of the settings and make up an important class of rock-forming hedyphane group in the apatite supergroup. This new minerals. The standard formula for the apatite supergroup mineral is named “miyahisaite” in honor of Professor IX VII−IX minerals is M12 M23(TO4)3X, and they are formally Michitoshi Miyahisa (1928-1983), who contributed great- divided into five groups based on their crystallographic ly to the advancement of mineralogy, petrology, and eco- and chemical features: the apatite, hedyphane, belovite, nomic geology in Japan through his research on many ore britholite, and ellestadite groups. Although the minerals deposits on Kyushu. The data and name were approved can incorporate various M-type cations such as Ca, Sr, by the IMA Commission on New Minerals, Nomenclature Ba, and Pb, the cation size mismatch causes site splitting and Classification (IMA2011-043). The type specimen of and cation ordering (Pasero et al., 2010). M-type cations miyahisaite has been stored at the National Museum of are disordered and ordered in the apatite and hedyphane Nature and Science, Tokyo, Japan (NSM M-41299). groups, respectively, since large cations are placed in the Here, we describe the new mineral, miyahisaite. M2 site after the M1 site is filled by the smaller cations in the P63/m structure. Indeed, Ca and Pb ordering in the OCCURRENCE structures of the hedyphane group due to the cation size mismatch and Ca-Sr ordering are also expected to poten- Many manganese ore deposits are embedded in the chert tially produce new mineral species in the hedyphane of Triassic to Jurassic age distributed in the Chichibu belt group. In the present study, we found a new Sr-Ba fluoro- of the Saiki area, Oita, Japan (Yoshimura, 1969). A low- , (Sr,Ca)2Ba3(PO4)3F, from the Shimoharai grade metamorphism of prehnite-pumpellyite to actinolite doi:10.2465/jmps.110901 facies has been recognized in this area (Imai et al., 1971). D. Hamane, [email protected] Corresponding author The Shimoharai mine exploits one of the bedded 122 D. Nishio-Hamane, Y. Ogoshi and T. Minakawa manganese deposits in the chert and is located in the available online from http://joi.jlc.jst.go.jp/JST.JSTAGE/ Yayoi Udoki area in Saiki City. Several ore deposits were jmps/110901). The braunite-rich layer is the main man­ also found in the same chert block (Yoshimura, 1969), ganese ore of the Shimoharai mine, and its constituents and unique Na-Mn pyroxene and Ba-rich minerals have are braunite and quartz in a matrix. Namansilite is an previously been found in the chert from the Shimoharai uncommon mineral in general in bedded manganese mine (Minakawa et al., 1994). The chert from the deposits, while it is a principal constituent of the chert Shimoharai mine is divided into three layers: black layer from the Shimoharai mine and is scattered in the braunite-rich, purple namansilite-rich, and brown quartz matrix. A small amount of fluorapatite is also found aegirine-rich layers (Fig. 1; Color version of Figure 1 is only in this layer. The aegirine-rich layer crosses the other layers as a vein and includes a negligible amount of quartz, while its main constituents are aegirine and cymrite. Rare Ba-rich minerals such as strakhovite, benitoite, and have been also found in this layer. Noélbensonite, a quite rare Ba-rich mineral, also occurs in the aegirine- rich layer, and it forms aggregates of up to 5 mm in size at the boundary between the aegirine-rich layer and the other layers (Minakawa, 1995). After the layer formation, a several-millimeter-thick quartz-rich vein crosses the chert, and arfvedsonite with high K and Mn contents also occurs in this quartz-rich vein. The details of such rare minerals will be reported after future studies. Miyahisaite, a fluorophosphate of Ba and Sr, occurs in the namansilite-rich layer, although the other Ba-rich minerals occur in the aegirine-rich layer. It is scattered in Figure 1. Photograph of miyahisaite-bearing chert from the Shimo- the namansilite-rich layer along its boundary with the harai mine, Oita Prefecture, Japan. The chert consists mainly of aegirine-rich layer. Miyahisaite occurs in anhedral grains quartz and is divided into three layers: black braunite (Brn)-rich, with submicron to 10 μm sizes and forms aggregates up purple namansilite (Nm)-rich, and brown aegirine (Aeg)-rich to about 100 μm in size. It is closely associated with layers. Miyahisaite occurs in the namansilite-rich layer. Color version of Figure 1 is available online from http://joi.jlc. fluorapatite in the quartz matrix of the namansilite-rich jst.go.jp/JST.JSTAGE/jmps/110901. layer (Fig. 2). The miyahisaite partially or completely

Figure 2. Backscattered electron images of miyahisaite (Mh). Miyahisaite occurs as aggregates with fluorapatite up to about 100 μm in size in the quartz matrix in the namansilite-rich layer. Miyahisaite, a new mineral of the hedyphane group 123 replaces the fluorapatite, and relict fluorapatite pieces are vitreous and transparent. No fluorescence was observed often found in the miyahisaite aggregates (Fig. 2). No under long- or short-wave ultraviolet radiation. Its Mohs significant association with other minerals was found in hardness was measured to be 5 by scratch tests performed the investigated occurrences of miyahisaite. on the aggregates using small pieces of fluorite, apatite, and orthoclase feldspar. The density was calculated to be APPEARANCE AND PHYSICAL PROPERTIES 4.511 g/cm3 using an empirical formula. Other physical and optical properties could not be measured or observed Miyahisaite is colorless white in powder, and its luster is because of the small grain size.

Table 1. Representative chemical composition of miya- CHEMICAL COMPOSITION hisaite

The chemical analyses of miyahisaite were carried out using a JEOL JSM-5400 electron microprobe with an Oxford WDS 400 wavelength-dispersive spectroscopy (WDS; 15 kV, 10 nA, beam diameter 1-2 μm). The

standard materials used were CaSiO3, SrF2, BaF2, GaP, and NaCl for Ca, Sr and F, Ba, P, and Cl, respectively. Energy-dispersive spectroscopy (EDS) analyses (15 kV, 0.4-0.8 nA, beam diameter 1-2 μm) were also carried out to obtain the Ba-Sr-Ca ratio of miyahisaite. The representative chemical composition determined

by WDS is listed in Table 1. The H2O content was calculated as OH + F + Cl = 1 per formula unit by analogy with the apatite group minerals. The simplified and ideal formulae are different from each other: the

empirical formula is (Sr1.366Ca0.717)Σ2.083Ba2.911P3.002O12(F0.898

OH0.088Cl0.014)Σ1.00, leading a simplified formula of (Sr,Ca)2

Ba3(PO4)3F, and the ideal formula is written as Sr2Ba3

(PO4)3F, which requires 23.25 wt% SrO, 51.62 wt% BaO,

23.89 wt% P2O5, 2.13 wt% F, and −0.90 wt% F = O, for a * - - H2O is calculated as OH + F + Cl = 1. total of 100.00 wt%. Miyahisaite is a Sr and Ba

Figure 3. X-ray diffraction pattern for miyahisaite. Bars below the diffraction pattern indicate the peak positions after the refinement of the unit cell parameters for miyahisaite (top), fluorapatite (middle), and quartz (bottom). 124 D. Nishio-Hamane, Y. Ogoshi and T. Minakawa

Table 2. Powder XRD data for miyahisaite

dominant fluorophosphate member of the hedyphane CRYSTALLOGRAPHY group of minerals in the apatite supergroup. The angle-dispersive X-ray diffraction (XRD) pattern for Miyahisaite, a new mineral of the hedyphane group 125 miyahisaite was collected using the synchrotron X-ray (Sr + Ca):Ba = 2:3 (Fig. 4). Since the standard formula IX VII−IX source on the NE1 beam line of PF-AR, KEK, Japan. for the apatite supergroup minerals is M12 M23

This beam line provides a 30-μm-diameter collimated (TO4)3X, the compositional ratio of miyahisaite is in beam of monochromatized X-ray radiation (λ = 0.4111 harmony with the supergroup’s cation sites, as Sr + Ca Å). The XRD spectra were collected using the Debye- and Ba occupy the M1 and M2 sites, respectively. The Scherrer method and recorded using an imaging plate disorder and the order of the M-type cations are detector. The sample-to-detector distance and inclination individually distinguished to separate groups such as the of the detector were calibrated using a standard material apatite (disordered) and the hedyphane (ordered) group,

(CeO2). Two-dimensional XRD images were integrated even in the same symmetry (Pasero et al., 2010). The with respect to 2θ to obtain conventional one-dimensional cation size mismatch causes the ordering, because the M1 diffraction profiles using the IPAnalyzer and PDIndexer site is small and the M2 site is large, and small Ca and software developed by Seto et al. (2010). large Pb cations are ordered in the structures such as those The collimated X-rays irradiated the miyahisaite of the hedyphane group. Ca-Sr ordering is also expected aggregate on the slide glass from the slide side. Although to produce potentially new mineral species in the the background intensities were high because of the slide, hedyphane group due to this cation size mismatch (Pasero the diffraction pattern from miyahisaite was clearly et al., 2010). Figure 5 shows the ionic size ratios among observed, along with those of fluorapatite and quartz. The Ca, Sr, Ba, and Pb for different coordination numbers X-ray diffraction pattern after the subtraction of the based on results obtained by Shannon and Prewitt (1969). background is shown in Figure 3, and the XRD data are listed in Table 2. The eight strongest lines in the powder

XRD pattern [d (Å), (I/I0), hkl] are 3.427 (16) 102, 3.248 (22) 120, 2.981 (100) 121, 2.865 (21) 300, 1.976 (23) 123, 1.874 (16) 140, 1.870 (15) 004, and 1.864 (17) 402. The XRD peaks obtained for miyahisaite can be indexed using the hexagonal P63/m structure of the apatite supergroup, the unit cell parameters are a = 9.921 (2) Å, c = 7.469 (3) Å, and V = 636.7 (3) Å3, and Z = 2. The c/a ratio calculated from the unit cell parameters is 0.753.

DISCUSSION

Figure 4. Chemical variation of miyahisaite in the Ca-Sr-Ba sys- Miyahisaite is one of the fluorophosphate members in the tem. The dotted line indicates (Sr + Ca):Ba = 2:3. Miyahisaite apatite supergroup and is characterized by high amounts shows little chemical variation, and the compositions follow the of Ba and Sr with a small amount of Ca as (Sr,Ca)2Ba3 dotted line.

(PO4)3F. Miyahisaite would be compositionally indisti­ nguishable from the Ba and F analogs of stronadelphite

Sr5(PO4)3F and alforsite Ba5(PO4)3Cl of the apatite group

(Table 3), respectively, if it was described as (Ba,Sr,Ca)5

(PO4)3F. However, miyahisaite shows less chemical variation, and its compositions lie on the line indicating

Table 3. Comparative data on miyahisaite and other related miner- als of the apatite supergroup

Figure 5. Plot of ionic ratios for different coordination numbers based on the effective ionic radii obtained by Shannon and Pre- 1, Newberry et al., (1981); 2, Pekov et al., (2010). witt (1969). 126 D. Nishio-Hamane, Y. Ogoshi and T. Minakawa

The M sites in the apatite structure have seven to nine SUPPLEMENTARY MATERIAL coordinated sites, and the Ba/Sr ratios are similar to the Sr/Ca ratios for these coordination numbers. This suggests Color version of Figure 1 is available online from http:// that Ba and Sr may also prefer to be ordered in the apatite joi.jlc.jst.go.jp/JST.JSTAGE/jmps/110901. structure. On the other hand, the Sr/Ca ratio is considerably low in nine-coordinated sites such as the M1 REFERENCES site. This also suggests that a small amount of Ca can be easily accommodated in the M1 site even if Sr is dominant Imai, I., Teraoka, Y. Okumura, K. (1971) Geologic structure and in the M1 site. According to the allocation of ions to sites metamorphic zonation of the northeastern part of the Shi- manto terrene in Kyushu, Japan. Journal of the Geological in the apatite supergroup minerals, where the large cation Society of Japan, 77, 207-220 (in Japanese with English ab- is placed in the M2 site after the M1 site is filled by small stract). cations (Pasero et al., 2010), miyahisaite, (Sr,Ca)2Ba3 Kato, A., Matsubara, S. and Watanabe, T. (1987) Banalsite and se-

(PO4)3F, is considered to be a member of the hedyphane randite from the Shiromaru mine, Tokyo. Bulletin of the Na- group with an ordered structure rather than the apatite tional Science Museum, series C, 13, 107-114. Matsubara, S., Miyawaki, R., Tiba, T. and Imai, H. (2000) Tamai- group with a disordered structure, since Sr + Ca and Ba te, the Ca-analogue of ganophyllite, from the Shiromaru may occupy the M1 and the M2 sites, respectively. mine, Okutama, Tokyo, Japan. Journal of Mineralogical and Miyahisaite partially or completely replaces fluora­ Petrological Sciences, 95, 79-83. patite and occurs only in the boundary area between the Matsubara, S., Miyawaki, R., Yokoyama, K., Shimizu, M. and 3+ namansilite- and aegirine-rich layers, while fluorapatite is Imai, H. (2004) Tokyoite, BaMn (VO4)2(OH), a new mineral from the Shiromaru mine, Okutama, Tokyo, Japan. Journal of scattered throughout the whole namansilite-rich layer and Mineralogical and Petrological Sciences, 99, 363-367. was formed from radiolarians during the chert formation. Minakawa, T. (1995) Ba, Mn minerals from namansilite bearing The aegirine-rich layer crosses the namansilite-rich layer chert in Shimoharai mine. Abstracts of the Joint Fall Meeting and includes hydrous Ba-rich minerals as the main of The Japanese Association of Mineralogists, Petrologists constituent. Miyahisaite may have been formed by the and Economic Geologists, The Mineralogical Society of Ja- pan and The Society of Resource Geology, 59. reactions between fluorapatite and the fluid that caused Minakawa, T., Shinmyo, T. and Momoi, H. (1994) Namansilite the formation of the aegirine-rich layer during the late- from low grade metamorphosed bedded manganese ore de- stage activity. Although the intrusion of Ba-rich fluid is posits in Chichibu terrane of Kyusyu, Abstracts of the Joint quite unique even in manganese deposits, which often Fall Meeting of The Japanese Association of Mineralogists, show a wide variety, miyahisaite might be found in a Petrologists and Economic Geologists, The Mineralogical Society of Japan and The Society of Resource Geology, 83. similar geological setting. A similar deposit to this one at Newberry, N.G., Essen, E.J. and Peacor, D.R. (1981) Alforsite, a the Shimoharai mine has been found at the Shiromaru new member of the apatite group: the barium analogue of mine, Tokyo, Japan. The Shiromaru mine deposit is chlorapatite. American Mineralogist, 66, 1050-1053. located in the Chichibu belt of Jurassic age, consists of Pasero, M., Kampf, A.R., Ferraris, C., Pekov, I.V., Rakovan, J. and bedded manganese chert in association with Ba-rich White, T.J. (2010) Nomenclature of the apatite supergroup minerals. European Journal of Mineralogy, 22, 163-179. minerals, and has experienced low-grade metamorphism Pekov, I.V., Britvin, S.N., Zubkova N.V., Pushcharovsky, D.V., (e.g., Kato et al., 1987; Matsubara et al., 2000; 2004), just Pasero, M. and Merlino, S. (2010) Stronadelphite, Sr5(PO4)3F, like the deposits from the Shimoharai mine. Further a new apatite-group mineral. European Journal of Mineralo- surveys searching for minerals from the Shimoharai and gy, 22, 869-874. Shiromaru mines are highly desirable to help us Seto, Y., Nishio-Hamane, D., Nagai, T. and Sata, N. (2010) Devel- opment of a software suite on X-ray diffraction experiments. understand the peculiar activity of Ba-rich fluid on the The Review of High Pressure Science and Technology, 20, bedded manganese chert deposit in the Chichibu belt. 269-276 (in Japanese with English abstract). Shannon, R.D. and Prewitt, C.T. (1969) Effective ionic radii in ACKNOWLEDGMENT oxides and fluorides. Acta Crystallographica B, 25, 925-946. Yoshimura, T. (1969) Supplement to “Manganese ore deposits of Japan”, Part II. The science reports of the Faculty of Science, We are grateful to T. Yagi for his help on the synchrotron Kyushu University, Geology 9, 487-1004. X-ray experiment, which was conducted under the auspices of proposal 08G042. We are grateful to the Manuscript received September 1, 2011 anonymous referees and the editor for their constructive Manuscript accepted March 1, 2012 reviews. D. N.-H. is supported by a Grant-in-Aid for Published online May 30, 2012 Young Scientists B (Grant No. 23740389) from the Japan Manuscript handled by Hiroki Okudera Society for the Promotion of Science.