地学雑誌 Journal of Geography（Chigaku Zasshi） 130（3）369­378 2021 doi:10.5026/jgeography.130.369

Dalyite（ K2ZrSi6O15） and Zektzerite（ LiNaZrSi6O15） in Aegirine-bearing Albitite from Iwagi Islet, SW Japan

＊ ＊＊ ＊ Teruyoshi IMAOKA , Sachiho AKITA and Mariko NAGASHIMA

［Received 16 October, 2020; Accepted 15 January, 2021］

Abstract The rare potassium zirconium silicate dalyite and lithium sodium zirconium silicate zektze- rite have been found in Cretaceous aegirine albitite from Iwagi Islet, Southwest Japan. Electron microprobe analyses of the dalyite and zektzerite yielded the following empirical formulas based

on 15 oxygens: （K1.93Ba0.01）S1.94（Zr0.99Hf0.02）S1.01Si5.98O15 and Na1.03（Zr0.96Hf0.02Y0.01Sc0.01）S1.00Li1.02

（Si5.95Al0.04）S5.99O15, respectively. The occurrence of porous zircon, dalyite, and mantles of zektze- rite on resorbed zircon in the albitite suggests that those zirconosilicate minerals are the prod- ucts of metasomatic mineral replacement reactions by Na-, K-, and Li-rich hydrothermal fluids. This is the first documented occurrence of dalyite and zektzerite in the Japanese Islands.

Key words： dalyite, zektzerite, albitite, Li-metasomatism, Iwagi Islet

It also occurs in a block of peralkaline pegma- I. Introduction tite in the moraine of the Dara-i-Pioz glacier,

Dalyite, K2ZrSi6O15, was first discovered in northern Tajikistan （Grew et al., 1993）, in peralkaline granite xenolith from Ascension the fluorite-bearing biotite syenogranite of the Island（ Van Tassel, 1952）. Since then, it has Cretaceous Del Salto pluton in the Patagonian been reported as an accessory mineral in a va- batholith, Aysén Province, Chile（ Welkner et al., riety of peralkaline silica-oversaturated rocks, 2002）, in the nepheline syenite pegmatite at including peralkaline granites, syenites, peg- Virikkollen, Haneholmveien, and Sandefjord in matites, charoitites, lamproites, lamprophyres, Norway, as euhedral crystals at Ampasibitika fenites, and carbonatites （see Jeffery et al., on the Ampasindava Peninsula, Madagascar, 2016 and references therein）. It is often asso- and as gemmy crystals up to 3 cm across at Mt ciated with chevkinite-（Ce）, aegirine, quartz, Malosa in Malawi1）. and britholite. The peculiar metasomatic rocks （albitites）

Zektzerite, LiNa（Zr,Ti,Hf）Si6O15, is a very on Iwagi Islet（ 34°15¢47²N, 133°9¢39²E）, Ehime rare mineral that occurs in peralkaline granites Prefecture, Japan, have been studied by Sugi and syenites in association with arfvedsonite, and Kutsuna（ 1944）, Taneda（ 1950, 1952）, and ferrorichterite, astrophyllite, okanoganite, el- Murakami and Matsunaga（ 1966）. They con- pidite, aegirine, riebeckite, pyrochlore, sogdian- tain rare（ unusual） Li-rich silicates, including ite, and zircon. It was first found in miarolitic katayamalite（ KLi3Ca7Ti（2 SiO3）12（OH）2; Mura- cavities in the agpaitic granite of the Golden kami et al., 1983; Andrade et al., 2013）, sugilite 3+ 3+ Horn batholith, Washington（ Dunn et al., 1977）. （Na2K（Fe , Mn , Al）2Li3Si12O30; Kato et al.,

＊ Graduate School of Science and Technology for Innovation, Yamaguchi University, Yamaguchi, 753-8512, Japan ＊＊ Asahi Consultant Co., Ltd., Tottori, 680-0911, Japan

― 369 ― 1976; Murakami et al., 1976; Armbruster around Mt Sekizen-san. Dikes of granophyre, and Oberhänsli, 1988）, and murakamiite（ Li- diorite porphyry, and granite porphyry cut these

analogue of pectolite, LiCa2Si3O（8 OH）; Imaoka granites. et al., 2017）, and their mineralogical diversity The albitites occur as many small discrete is unique. During our chemical and mineralog- masses in the coarse-grained biotite granite ical studies of the albitites from Iwagi Islet, we around the summit of Mt Kuresaka in the east- found the rare Zr-bearing minerals dalyite and ern part of the islet（ Fig. 1c）. The largest body zektzerite. In this paper, we will describe the of albitite is several tens of meters in diameter, occurrence and chemical compositions of these and small albitite bodies, up to several tens minerals and discuss their metasomatic forma- of centimeters to meters wide are generally tion. oriented more-or-less N­S, and irregularly distributed over an area of 1.5 ´ 0.8 km2. The II. Geological setting relationships between the albitites and the sur- Small bodies of metasomatites are distribut- rounding coarse-grained granite are transition- ed in the Setouchi area, SW Japan（ Fig. 1a）. al, so that albitized granite and quartz albitite They are known from seventeen areas and can be found between them. No intrusive con- occur in the granitoids of the Cretaceous Ryoke tact was found between them. and San-yo belts. The modes of occurrence, III. Petrography petrography, and major element chemistry of some of these metasomatites have been describ- Sample IWG-23, a dalyite­zektzerite-bearing ed by Murakami（ 1976 and references therein）, albitite, was collected from the top of Mount Murakami and Matsunaga（ 1966）, and Mina- Kuresaka at the eastern end of Iwagi Islet. kawa et al. （1978）. According to Murakami Albite is the dominant mineral in the albitite, （1976）, the metasomatites commonly form and white to transparent albite and black aegi- small bodies less than 100 m across that are rine are visible to the naked eye. The minerals pipe-like, irregular sheets, or ovoid in shape. present include albite（ 99.7％）, alkali-feldspar The geology of Iwagi Islet and its peculiar （0.2％）, quartz（ 0.1％）, and aegirine（ < 0.1％）. albitites has recently been described in detail The albite（ 0.2­6 mm） is subhedral­anhedral, by Imaoka et al.（ 2021）. Thus, only an outline and it forms aggregates of numerous, small, of the geology of the islet is provided in this granular crystals at the boundaries of large, paper. The Ryoke metamorphic rocks, made up broken, and deformed albite grains. Magmatic of schistose hornfelses derived from slates and quartz shows variable degree of dissolution

sandstones, are the oldest rocks on the islet. and changed to secondary opal （SiO2∙nH2O） These occur in the central summit area of the （Imaoka et al., 2021）, which is termed “dequart- islet, and in the southwestern coastal area. zification” （e.g., Cathelineau, 1986; Boulvais Granitoids intrude the Ryoke rocks and are et al., 2007; Nishimoto et al., 2014; Figs. 2a, distributed extensively throughout the islet. b, and c）. They present in some vug and pore They can be divided into three types, coarse-, （Figs. 2a, b, and c）. Even with this sample, medium-, and fine-grained biotite granite, in quartz（ 0.5­1.7 mm） is opalized, and occurs as order of emplacement （Fig. 1b）. The coarse- prismatic and/or spherical crystals associated grained biotite granite occurs in the eastern with aegirine and an unknown Si­Fe­K­Al and northern parts of the islet as sheets in mineral. The aegirine（ 0.01­0.3 mm） occurs as the topographically lower part of the medium- anhedral aggregates and/or independent euhe- grained granite, and the sheets are accompa- dral­anhedral grains, and it is often associated nied by pockets or dikes of aplite and pegma- with the opalized quartz and unknown Si­Fe­ tite. The fine-grained granite forms a sheet in K­Al mineral（ Fig. 2a）. Small amounts of K- the upper part of the medium-grained granite feldspar occur as anhedral crystals included in

― 370 ― Fig. 1 （ a） Distribution of metasomatic rocks in Setouchi Province, SW Japan.（ b） Geological map of Iwagi Islet, Ehime Prefecture, Japan（ Imaoka et al., 2021）.（ c） Enlarged view of the area around Mount Kuresaka showing the occurrence of small masses of albitite, along with the location of the studied dalyite­zektzerite-bearing albitite sample no. IWG-23.

― 371 ― Fig. 3 Backscattered electron images of an anhedral dalyite crystal filling an interstitial space （a）, and zektzerite including porous zircon（ b） from the albitite on Iwagi Islet, Ehime Prefecture, Japan. Abbreviations: Dal = dalyite, Zr = zircon, Zek = zektzerite, Ab = albite, Mnz = monazite.

the quartz and albite. The accessory minerals present include a sogdianite-like mineral（ Fig. 2c）, zircon, fluora- patite, calcite, britholite-（Ce）, monazite-（Ce）, turkestanite, dalyite（ Fig. 3a）, zektzerite（ Fig. 3b）, and unknown Si­Fe­K­Al and Si­Th­Ca Fig. 2 Backscattered electron images showing the dis- minerals. The sogdianite-like mineral （4­110 solution of magmatic quartz.（ a） Opalized quartz μm） is heterogeneous in appearance, and often filling a vug with aegirine­augite and a minute associated with the opalized quartz. The zircons Si­Fe­K­Al-mineral.（ b） Opal filling a vug that （3­40 μm） are euhedral­anhedral, and often formed among albite crystals.（ c） Opalized quartz that exhibits a fine fibrous mesh texture and a enclosed by the sogdianite-like mineral. Porous sogdianite-like mineral. Abbreviations: Opl = zircon is commonly observed（ Fig. 3b）. The flu- opal, Ab = albite, Agt = aegirine­augite, Sog = orapatite（ 3­15 μm across） occurs as euhedral­ sogdianite-like mineral, SFK = Si­Fe­K­Al min- anhedral crystals in the albite, and it is often eral. associated with K-feldspar. The calcite（ 12­30 μm across） occurs in the albite with the K-feld- spar. The britholite-（Ce）（ 2­22 μm） occurs as

― 372 ― anhedral grains at the grain boundaries of the 0.01 and 0.01 apfu, respectively） also indicate a quartz and K-feldspar. The monazite-（Ce）（ 4­ limited substitution for K（ Table 1）. From the 11 μm across） is heterogeneous in appearance, analyses, the empirical formula based on 15 O and it occurs in the albite, often associated with apfu is（ K1.93Na0.01Ba0.01）S1.95（Zr0.99Hf0.02Ti0.01）S1.02 zircon. The dalyite was observed as an anhedral Si5.98O15, which is close to the ideal formula of colorless grain 14 ´ 29 μm in size enclosed by dalyite. Jeffery et al.（ 2016） classified dalyites the albite（ Fig. 3a）. The zektzerite（ 10­65 μm） based on K ↔ Na substitution within the poly- occurs either as independent grains enclosed by hedral sites into Group 1, with an abundance of the albite or as grains within the albites that Na（ 0.12­0.19 apfu）, and Group 2, with signifi- enclose grains of zircon（ Fig. 3b）. The unknown cantly lower concentrations of Na（ < 0.015­0.03 Si­Fe­K­Al mineral（ 3.8­17 μm） is anhedral. apfu）. The Iwagi dalyite belongs to Group 2.

The unknown Si­Th­Ca mineral（ 3.8­17 μm） 2） Zektzerite（ NaZrLiSi6O15） is heterogeneous in appearance and occurs as Representative analyses of the zektzerite anhedral crystals within the quartz. are listed in Table 1, and we note that the Li2O value（ 2.82 wt.％） is taken from Dunn et al. IV. Mineral chemistry （1977）. The chemical composition can be sum-

The chemical compositions of the minerals marized as follows: SiO2 66.3 wt.％, Na2O 5.9 were determined on a polished section using a wt.％, ZrO2 21.9 wt.％, Li2O 2.82 wt.％, and

JXA-8230 electron microprobe analyzer（ EMPA） trace amounts of HfO2 （0.75 wt.％）, Al2O3 at Yamaguchi University, Japan. The operating （0.35 wt.％）, and FeO （0.09 wt.％）. Only conditions were as follows: an accelerating volt- minor substitution of hafnium for zirconium age of 15 kV, a beam current of 20 nA, and a is indicated. The empirical formula based on beam diameter of 1 μm. Wavelength­dispersion 15 O apfu is Na1.03（Zr0.96Hf0.02Y0.01Sc0.01）S1.00Li1.02 spectra were collected with LIF, PET, and TAP （Si5.95Al0.04）S5.99O15. X-ray diffraction data and crystals to identify interfering elements, and analytical data of Li contents are not available to locate the best wavelengths for background due to the small size and low modal ratio of the measurements. The probe standards used for mineral, but no minerals with the same ele- the measured elements are described in Naga- ment ratio are known other than zektzerite. shima et al.（ 2013）. The measured intensities V. Discussion of EuLα 1 and GdLα 1 were corrected for peak- overlap interference of PrLβ 2 for Eu and LaLβ 2 Mineral replacement reactions take place and CeLγ 1 for Gd using JEOL software. The primarily by dissolution­reprecipitation pro- microprobe data were processed by an on-line cesses associated with fluid­rock interactions computer using the ZAF correction method. and metasomatism（ Putnis, 2002）, and import- The analytical errors estimated from the repro- ant evidence for these processes is the presence ducibility observed in multiple measurements of pores（ including micropores） in the metaso- were ±2％ for major elements and ±5％ for matic minerals. Recent experimental studies trace elements. confirmed that reactions between minerals and

1） Dalyite（ K2ZrSi6O15） a fluid phase commonly involve a pseudomor- Representative analyses of the dalyite are phic replacement via an interface-coupled dis- listed in Table 1. The composition can be sum- solution­reprecipitation process（ e.g., Labotka marized as follows: SiO2 62.0 wt.％, K2O 15.7 et al., 2004; Putnis et al., 2007; Niedermeier et wt.％, ZrO2 21.0 wt.％, and HfO2 0.74 wt.％. al., 2009）. Albitization in granites causes an The low contents of Ti and Hf（ up to 0.01 and overall change in bulk composition dominat- 0.02 apfu, respectively）, indicate that the re- ed by the production of Na-rich minerals in placement of Zr by Ti and Hf is limited. The in- the rock with a concomitant removal of K by significant concentrations of Ba and Na（ up to the fluid. Engvik et al.（ 2008） suggested that

― 373 ― Table 1 Representative chemical compositions of dalyite and zektze- rite in an albitite（ IWG-23） from Iwagi Islet, Ehime Prefec- ture, Japan. Dalyite（ 23-081） Zektzerite（ 23-032） Oxide（ wt.％） O = 15 Oxide（ wt.％） O = 15

SiO2 62.00 Si 5.976 SiO2 66.32 Si 5.949

TiO2 0.09 Ti 0.007 TiO2 0.00 Ti 0.000

Al2O3 0.02 Al 0.002 Al2O3 0.35 Al 0.037 3+ 3+ Cr2O3 0.00 Cr 0.000 Cr2O3 0.03 Cr 0.002 3+ 3+ V2O3 0.05 V 0.003 V2O3 0.00 V 0.000 FeO 0.04 Fe2+ 0.003 FeO 0.09 Fe2+ 0.007 MnO 0.03 Mn2+ 0.002 MnO 0.00 Mn2+ 0.000 MgO 0.02 Mg 0.002 MgO 0.00 Mg 0.000 BaO 0.15 Ba 0.006 BaO 0.03 Ba 0.001

Na2O 0.06 Na 0.011 Na2O 5.91 Na 1.028

K2O 15.67 K 1.927 K2O 0.01 K 0.001

ZrO2 21.02 Zr 0.988 ZrO2 21.94 Zr 0.960

HfO2 0.74 Hf 0.020 HfO2 0.75 Hf 0.019

Sc2O3 0.01 Sc 0.001 Sc2O3 0.02 Sc 0.002

Y2O3 0.00 Y 0.000 Y2O3 0.18 Y 0.009

La2O3 0.00 La 0.000 La2O3 0.05 La 0.002

Ce2O3 0.04 Ce 0.001 Ce2O3 0.03 Ce 0.001

Pr2O3 0.01 Pr 0.000 Pr2O3 0.05 Pr 0.002

Sm2O3 0.05 Sm 0.002 Sm2O3 0.00 Sm 0.000

Lu2O3 0.00 Lu 0.000 Lu2O3 0.21 Lu 0.006

Nb2O5 0.03 Nb 0.001 Nb2O5 0.07 Nb 0.003

ThO2 0.00 Th 0.000 ThO2 0.03 Th 0.001

UO2 0.02 U 0.000 UO2 0.00 U 0.000

Li2O n.d. Li ­ Li2O 2.82 Li 1.017 F 0.11 Total 8.954 F 0.08 Total 9.047 -O º F 0.05 F 0.033 -O º F 0.04 F 0.023 Total 100.11 Total 98.97

an interface-coupled dissolution­reprecipitation that may resemble pseudomorphs. mechanism is responsible for the coupled ex- The principal Zr-bearing minerals in the Iwagi + 4+ 2+ 3+ change of Na and Si for Ca and Al during albitites include zircon（ ZrSiO4）, sogdianite-like

the albitization of plagioclase. minerals（ Fig. 2c）, dalyite（ K2ZrSi6O15; Fig. 3a）,

Pseudomorphs are clear examples of disso- zektzerite（ LiNaZrSi6O15; Fig. 3b）, baddeleyite

lution­reprecipitation（ Putnis, 2002）. The key （ZrO2）, and gittinsite （CaZrSi2O7） （Imaoka, feature of a pseudomorph is the preservation of unpublished data）. Among these, zircon is the the shape（ and volume） of the parent crystal most ubiquitous in all the samples we studied. （Putnis, 2002）. In the Iwagi albitite, magmatic The most important observations we made on quartz was dissolved（ Fig. 2）, and the resulting the petrography and chemistry of the zirconium- vugs were often filled by metasomatic minerals bearing minerals in the albitites are as follows: such as opal, aegirine, murakamiite, Li-rich （1） porous zircon is commonly observed in the pectolite, and sugilite （Imaoka et al., 2021） albitite （Fig. 3b）, but not in the host biotite

― 374 ― granite where the zircons have well-developed quartz in the albitite are only 0.2％ and 0.1％, crystal shapes and show oscillatory zoning respectively, indicating that the original large indicating a magmatic origin, （2） mantles of amounts of K-feldspar （20­38％） and quartz zektzerite on porous zircon are found in the （36­45％） in the host granite were lost during + + albitite（ Fig. 3b）, and（ 3） the dalyite occurs in an outflow of K and SiO2 and an inflow of Li a small pore in the albitite（ Fig. 3a）, and its and Na+ in hydrothermal fluids, thereby facili- composition is close to the ideal, with a low Na tating the growth of zektzerite and dalyite. content（ < 0.015 to 0.03 apfu）. Observation（ 1） Jeffery et al.（ 2016） divided dalyite into two suggests that the early crystallized zircon in types based on the Na ↔ K substitution: the the host granite became unstable and porous sodic Group 1 type is characterized by rela- due to the instability of zircon in alkaline­ tively high Na contents（ 0.12­0.19 apfu） and peralkaline solutions and fluids（ Watson, 1979; the potassic Group 2 type by low Na contents Geisler et al., 2007; Grimes et al., 2009）. Obser- （< 0.015­0.03 apfu）. Generally, the dalyite vation（ 2） implies that the zircons were read- found within peralkaline granites and syenites ily dissolved during albitization and that the is defined by a higher K ↔ Na substitution chemical compositions of the Li­Na-rich fluids relative to the dalyite found in highly potassic were different enough to induce the resorption rocks（ Jeffery et al., 2016）. It seems strange at of the early zircon. From observation （2） we first that the dalyite in the sodic Iwagi albitite conclude that the zektzerite is a metasomatic is the potassic Group 2 type dalyite. Harris and rather than a magmatic mineral. We propose Rickard（ 1987） also noted that the Straums- the following metasomatic reaction for the for- vola dalyite has no Na content, despite the rock

mation of zektzerite in an open system: having a high Na2O/K2O ratio of 1.35（ Na2O = 6.00, K O = 4.44 wt.％）. They suggested that ZrSiO + 5SiO + Li+ + Na+ + 2OH- 2 4 2 dalyite is stable near the liquidus for a wide zircon quartz range of K concentrations. From such data and = + LiNaZrSi6O15 H2O （1） suggestions, the chemical compositions of the zektzerite Straumsvola and Iwagi dalyites may reflect The observed dissolution of magmatic quartz another potential control（ e.g., temperature） in （Fig. 2） is consistent with the above reaction, addition to whole-rock chemistry.

according to which SiO2（ quartz） is consumed. Imaoka et al.（ 2021） inferred that the large The occurrence of anhedral dalyite in a small Li isotope fractionation of murakamiite and Li- pore （observation 3） indicates that it formed rich pectolite on Iwagi Islet could be attributed as a result of metasomatism by the interstitial to metasomatic hydrothermal fluid­rock inter- solution trapped in the pore. The formation of actions at 300­600°C. Dalyite has been synthe- dalyite in the albitite can be explained by the sized hydrothermally at 340°C and 600 bars following reaction: （Caruba et al., 1970）, which would suggest that the metasomatic formation of dalyite took place ZrSiO + 5SiO + 2K+ + 2OH- 4 2 at a relatively low temperature during the par- zircon quartz agenetic sequence of events that formed the al- = + K2ZrSi6O15 H2O （2） bitite. Under such low-temperature conditions, dalyite dalyite of potassic Group 2 is stable, and very The observed dissolution of magmatic quartz limited substitution of Na for K can occur. The （Fig. 2） also provides evidence for this pro- dalyite occurring in metasomatic rocks such as posed reaction. It is possible to estimate the the Iwagi albitite shows more limited miscibil- amounts of primary high-temperature phases ity than that shown by the same minerals in （K-feldspar, quartz, and zircon） that were dis- igneous rocks. solved, as the modal amounts of K-feldspar and With regard to dalyite:（ 1） on Iwagi Islet it

― 375 ― occurs only in the metasomatic albitite, and it K2ZrSi6O15. Données radiocrystallographiques. C.R. does not occur in the host granite;（ 2） dalyite Academie des Sciences, Paris 270, sér. D, 2741­ 2744.（ in French） on the Azores was inferred to be the last miner- Cathelineau, M.（ 1986）: The hydrothermal alkali al to crystallize（ Ridolfi et al., 2003）, as in our metasomatism effects on granitic rocks: Quartz dis- samples; （3） Furnes et al. （1982） suggested solution and related subsolidus changes. Journal of that dalyite in the ultrapotassic Sunnfjord dike Petrology, 27, 945­965. was either metasomatic in origin or, if magmat- Engvik, A.K., Ihlen, P.M. and Austrheim, H.（ 2008）: Albitization of granitic rocks: The mechanism of ic, that it had been altered by metasomatism; replacement of oligoclase by albite. Canadian Min- and （4） analytical data, possibly recording eralogist, 46, 1401­1415. metasomatism, frequently exhibit Na contents Dunn, P.J., Rouse, R.C., Cannon, B. and Nelen, J.A. below the detection level（ Jeffery et al., 2016）. （1977）: Zektzerite: a new lithium sodium zirconi- um silicate related to tuhualite and the osumilite Taking these results and our data into account, group. American Mineralogist, 62, 416­420. we conclude that the dalyite in the Iwagi albi- Furnes, H., Mitchell, J.G., Robins, B., Ryan, P. and tite is metasomatic in origin. Skjerlie, F.J.（ 1982）: Petrography and geochem- In summary, the Iwagi albitites record the istry of peralkaline, ultrapotassic syenite dykes of Zr-mineral replacement reactions that occurred Middle Permian age, Sunnnfjord, West Norway. Norsk Geologisk Tidsskrift, 62, 147­159. via dissolution­reprecipitation and changed the Geisler, T., Schaltegger, U. and Tomaschek, F.（ 2007）: original magmatic mineralogy of the host gran- Re-equilibration of zircon in aqueous fluids and melt. ite during hydrothermal activity. Element, 3, 43­50. Grew, E.D., Belakovskiy, D.I., Fleet, M.E., Yates, M.G., McGee, J.J. and Marquez, N.（ 1993）: Reed- Acknowledgments mergnerite and associated minerals from peralka- We are grateful to the Educational Board of Ehime line pegmatite, Dara-i-Pioz, southern Tien Shan, Prefecture and Kamishima-cho for permission to Tajikistan. European Journal of Mineralogy, 5, 971­ collect samples. The EMPA analyses were support- 984. ed by Yoji Morifuku of Yamaguchi University. The Grimes, C.B., John, B.E., Cheadle, M.J., Mazdab, manuscript was improved by constructive comments F.K., Wooden, J.L., Swapp, S. and Schwartz, J.J. from Takuya Echigo and an anonymous reviewer. We （2009）: On the occurrence, trace element geochem- also thank Kenichiro Tani for his editorial handling. istry, and crystallization history of zircon from in This work was supported by JSPS KAKENHI Grants situ ocean lithosphere. Contributions to Mineralogy and Petrology, 158, 757­783. （Numbers JP15K05314 and JP18K03806）. Harris, C. and Rickard, R.S.（ 1987）: Rare-earth rich Notes eudialyte and dalyite from a peralkaline granite dyke at Straumsvola, Dronning Maud Land, Ant- 1） http://www.mindat.org/min-4390.html［ Cited 2020/ arctica. Canadian Mineralogist, 25, 755­762. 10/16］. Imaoka, T., Nagashima, M., Kano, T., Kimura, J-I., References Chang, Q. and Fukuda, C.（ 2017）: Murakamiite, LiCa Si O（OH）, a Li-analogue of pectolite, from Andrade, M.B., Doell, D., Downs, R. and Yang, 2 3 8 the Iwagi Islet, southwest Japan. European Jour- H.（ 2013）: Redetermination of katayamalite, nal of Mineralogy, 29, 1045­1053. KLi Ca Ti（SiO ）（OH）. , 3 7 2 3 12 2 Acta Crystallographica Imaoka, T., Kimura, J.-I., Chang, Q., Ishikawa, T., , i41. E69 Nagashima, M. and Takeshita, N.（ 2021）: Chemical Armbruster, T. and Oberhänsli, R.（ 1988）: Crystal and lithium isotope characteristics of murakamiite chemistry of double-ring silicates: structures of and Li-rich pectolite from Iwagi Islet, southwest sugilite and brannockite. American Mineralogist, Japan. Journal of Mineralogical and Petrological 73, 595­600. Sciences, 116, 9­25. Boulvais, P., Ruffet, G., Cornichet, J. and Mermet, M. Jeffery, A.J., Gertisser, R., Jackson, R.A., O’Driscoll, （2007）: Cretaceous albitization and dequartzifi- B. and Kronz, A.（ 2016）: On the compositional cation of Hercynian peraluminous granites in the variability of dalyite, K2ZrSi6O15: A new occurrence Salvezines Massif（ French Pyrénées）. Lithos, 93, from Terceira, Azores. Mineralogical Magazine, 80, 89­106. 547­565. Caruba, R., Baumer, A. and Turco, G.（ 1970）: Kato, T., Miúra, Y. and Murakami, N.（ 1976）: The Première synthèse hydrothermale de la dalyite crystal structure of sugilite. Mineralogical Journal,

― 376 ― 8, 184­192. Nishimoto, S., Yoshida, H., Asahara, Y., Tsuruta, T., Labotka, T.C., Cole, D.R., Fayek, M., Riciputi, L.R. Ishibashi, M. and Katsuta, N.（ 2014）: Episyenite and Stadermann, F.J.（ 2004）: Coupled cation and formation in the Toki granite, central Japan. Con- oxygen-isotope exchange between alkali feldspar tributions to Mineralogy and Petrology, 167, 960. and aqueous chloride solution. American Mineralo- Putnis, A.（ 2002）: Mineral replacement reactions: gist, 89, 1822­1825. From macroscopic observations to microscopic Minakawa, T., Momoi, H. and Noto, S.（ 1978）: Rare mechanisms. Mineralogical Magazine, 66, 689­708. element minerals from pegmatites in the Ryoke Putnis, A., Hinrichs, R., Putnis, C.V., Golla­Schindler, Belt, western Shikoku, Japan. Memoirs of Ehime U. and Collins, L.G.（ 2007）: Hematite in porous red- University, Science, Series D, 8, 1­25.（ in Japanese clouded feldspars: Evidence of large-scale crustal with English abstract） fluid­rock interaction. Lithos, 95, 10­18. Murakami, N.（ 1976）: Paragenetic relations of main Ridolfi, F., Renzulli, A., Santi, P. and Upton, B.G.J. constituent minerals in metasomatic syenitic rocks （2003）: Evolutionary stages of crystallization of in Japan. in Progress in Research on Rock Forming weakly peralkaline syenites: Evidence from ejecta Minerals edited by Tomisaka, T., Journal of Japa- in the plinian deposits of Agua de Pau volcano（ Sao nese Association of Mineralogists, Petrologists and Miguel, Azores Islands）. Mineralogical Magazine, Economic Geologists, Special Paper, 1, 261­281.（ in 67, 749­767. Japanese） Sugi, K. and Kutuna, M.（ 1944）: Aegirine syenite from Murakami, N. and Matsunaga, S.（ 1966）: Petrologi- Iwaki Islet, Ehime Pref. Journal of Japanese Asso- cal studies on the metasomatic syenites in Japan. ciation of Mineralogists, Petrologists and Economic Part 2. Petrology of the aegirine syenite from Iwagi Geologists, 31, 209­224.（ in Japanese） Islet, Ehime Prefecture, Japan. Science Report of Taneda, S.（ 1950）: Aegirine syenite from Iwaki I., Yamaguchi University, 16, 17­33. Ehime Pref. Japan. Dedicated to the memory of the Murakami, N., Kato, T., Miura, Y. and Hirowatari, F. late Professor K. Sugi. Journal of Japanese Asso- （1976）: Sugilite, a new silicate mineral from Iwagi ciation of Mineralogists, Petrologists and Economic Islet, Southwest Japan. Mineralogical Journal, 8, Geologists, 34, 6­12.（ in Japanese） 110­121. Taneda, S.（ 1952）: Pectolite- and eudialite-like Murakami, N., Kato, T. and Hirowatari, F.（ 1983）: mineral-bearing aegirine syenite from Iwaki islet, Katayamalite, a new Ca­Li­Ti silicate mineral Setouchi（ Inland Sea）, Japan. Japanese Journal of from Iwagi Islet, Southwest Japan. Mineralogical Geology and Geography, 22, 235­240. Journal, 11, 261­268. Van Tassel, R.（ 1952）: Dalyite, a new potassium zir- Nagashima, M., Nishio­Hamane, D., Tomita, N., Mina- conium silicate, from Ascension Island, Atlantic. kawa, T. and Inaba, S.（ 2013）: Vanadoallanite- Mineralogical Magazine, 29, 850­857. （La）: A new epidote-supergroup mineral from Ise, Watson, E.B.（ 1979）: Zircon saturation in felsic liq- Mie Prefecture, Japan. Mineralogical Magazine, uids: Experimental results and applications to trace 77, 2739­2752. element geochemistry. Contributions to Mineralogy Niedermeier, D.R.D., Putnis, A., Geisler, T., Golla­ and Petrology, 29, 850­857. Schindler, U. and Putnis, C.V.（ 2009）: The mech- Welkner, D., Godoy, E. and Bernhardt, H.（ 2002）: anism of cation and oxygen isotope exchange in Peralkaline rocks in the Late Cretaceous Del Salto alkali feldspars under hydrothermal conditions. pluton, eastern Patagonian Andes, Aisén, Chile Contributions to Mineralogy and Petrology, 157, 65­ （47°35¢S）. Revista geológica de Chile, 29, 3­15. 76.

― 377 ― 岩城島産エジリンアルビタイト中のデーリー石とゼッツェル石

今 岡 照 喜＊ 秋 田 幸 穂＊＊ 永 嶌 真 理 子＊

愛媛県岩城島の白亜紀エジリンアルビタイトよ 孔質ジルコン，デーリー石，および不安定なジル り稀な K­Zr 珪酸塩鉱物であるデーリー石と Li­ コンを被覆するゼッツェル石の産状から，このア Na­Zr 珪酸塩鉱物であるゼッツェル石が見いださ ルビタイトは熱水活動時期における Na，K，Li れた。デーリー石とゼッツェル石の EPMA 分析 に富んだ流体によるジルコニウム鉱物の分解と沈

結果からそれぞれ（K1.93Ba0.01）S1.94（Zr0.99Hf0.02）S1.01 殿による交代反応の記録をよく保存している。こ

Si5.98O15 および Na1.03（Zr0.96Hf0.02Y0.01Sc0.01）S1.00 れは日本列島におけるデーリー石とゼッツェル石

Li1.02（Si5.95Al0.04）S5.99O15 の実験式が得られる。多 産出の最初の報告である。

キーワード：デーリー石，ゼッツェル石，アルビタイト，リチウム交代作用，岩城島

＊ 山口大学大学院創成科学研究科 ＊＊ アサヒコンサルタント株式会社

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