著者

Mutsuko INUI Ayato TANIFUJI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.113, no.4, pp.181-189, 2018 (Released:2018-09-09)

参考文献数

24

被引用文献数

3

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Traditional metamorphic geology admitted that the appearance of specific index mineral, such as garnet, indicated the rocks experienced higher peak metamorphic condition. It is largely true, but it is still unclear what is going on in the rocks at the very start of the garnet formation. One of the key must lie in the area where apparent isograd is outcropped. Nagatoro area is located in the Kanto Mountains, and it is where the low grade metamorphic rocks of the Sanbagawa metamorphic belt are exposed. Appearance of garnet is the index of the higher metamorphic grade in this area. Several outcrops in Nagatoro area are known to contain garnet, thus being good samples of the outcropped isograd. In this study, spatial distribution of garnet within such an outcrop several tens of meters long was investigated. The samples are pelitic schists, and the mineral assemblage was basically quartz, plagioclase, muscovite, and chlorite. 36 of the 55 samples contained garnet. Garnet grains were small, most of them with diameters less than 100 µm. Most of the garnet grains were euhedral to subhedral and were found within micaceous lamellae which form the foliations of the pelitic metamorphic rocks. The micaceous lamellae were constituted mainly by muscovite with lesser amount of chlorite. Occurrence of garnet–bearing rocks within the outcrop seemed to be restricted in certain structural layers. The structural layers are known to be nearly parallel to the lithologic boundary in this area. Mapped chemical profiles of garnet revealed that the garnet grains exhibited euhedral growth of the crystal. The core part was relatively large and homogeneous, with quite a high Mn end–member (spessartine) content (XSps > 50%). Irregular shaped inner core was preserved. These features indicate that the texture preserves the beginning stage of garnet growth. The trend of chemical composition of garnet rim and adjacent chlorite is consistent with the bulk rock chemistry control. Spatial distribution of garnet, at the start of its growth, was probably controlled by the bulk rock chemistry.

著者

Tatsu KUWATANI Kenji NAGATA Kenta YOSHIDA Masato OKADA Mitsuhiro TORIUMI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.170923, (Released:2018-04-19)

被引用文献数

5

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Geothermometry and geobarometry are used to study the equilibration of mineral inclusions and their zoned host minerals, which provide information on the P–T conditions of inclusions at the time of their entrapment. However, reconstructing detailed P–T paths remains difficult, owing to the sparsity of inclusions suitable for geothermometry and geobarometry. We developed a stochastic inversion method for reconstructing precise P–T paths from chemically zoned structures and inclusions using the Markov random field (MRF) model, a type of Bayesian stochastic method often used in image restoration. As baseline information for P–T path inversion, we introduce the concepts of pressure and temperature continuity during mineral growth into the MRF model. To evaluate the proposed model, it was applied to a P–T inversion problem using the garnet–biotite geothermometer and the garnet–Al2SiO5–plagioclase–quartz geobarometer for mineral compositions from published datasets of host garnets and mineral inclusions in pelitic schist. Our method successfully reconstructed the P–T path, even after removing a large part of the inclusion dataset. In addition, we found that by using a probability distribution of the most probable P–T path, rather than a single solution, an objective discussion of the validity of the thermodynamic analysis is possible.

著者

MATSUBARA Satoshi MIYAWAKI Ritsuro YOKOYAMA Kazumi SHIMIZU Masaaki IMAI Hiroyuki

出版者

日本鉱物科学会

雑誌

Journal of mineralogical and petrological sciences (ISSN:13456296)

巻号頁・発行日

vol.99, no.6, pp.363-367, 2004-12-01

被引用文献数

2 9

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Tokyoite, Ba₂Mn³⁺(VO₄)₂(OH), the Mn³⁺-analogue of gamagarite, is found from the Shiromaru mine, Okutama, Tokyo, Japan. It is monoclinic, <i>P</i>2₁/<i>m</i>, <i>a</i> = 9.10(4), <i>b</i> = 6.13(2), <i>c</i> = 7.89(5) Å, β = 112.2(5)°, Z = 2. The strongest lines in the powder X-ray diffraction pattern are 3.73 (15) (111), 3.31 (100) (112), 3.08 (20) (020), 3.00 (16) (301, 212, 102), 2.90 (19) (120), 2.80 (62) (121, 300), 2.16 (18) (321), 1.963 (15) (204). Electron microprobe analysis gave V₂O₅ 31.77, SiO₂ 0.15, Al₂O₃ 0.07, Fe₂O₃ 2.33, Mn₂O₃ 11.27, CaO 0.07, BaO 51.91, SrO 0.22, Na₂O 0.13, H₂O (calc.) 1.59, total 99.51 wt. %, and lead to the empirical formula, (Ba_1.92Na_0.02Sr_0.01Ca_0.01)_Σ1.96(Mn³⁺_0.81Fe³⁺_0.17Al_0.01)_Σ0.99[(V_1.99Si_0.01)O_7.92](OH)_1.00 on the basis of V + Si = 2 and (OH) = 1. It is translucent and black red in color with a vitreous luster. The streak is dark brownish red and cleavage is not observed. The Mohs' hardness is about 4 to 4.5. The calculated density is 4.62 g/cm³. It has distinct pleochroism, from reddish orange to dark brownish red in thin section and the calculated mean refractive index is 2.03. It occurs as irregular grains under 15 μm, and the aggregates are up to 250 μ</i>m wide in association with braunite, hyalophane and tamaite. The mineral is formed under the later stage activity of low grade metamorphism.

著者

Satoshi MATSUBARA Ritsuro MIYAWAKI Kazumi YOKOYAMA Masaaki SHIMIZU Hiroyuki IMAI

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.99, no.6, pp.363-367, 2004 (Released:2005-01-07)

参考文献数

19

被引用文献数

3 9

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Tokyoite, Ba2Mn3+(VO4)2(OH), the Mn3+-analogue of gamagarite, is found from the Shiromaru mine, Okutama, Tokyo, Japan. It is monoclinic, P21/m, a = 9.10(4), b = 6.13(2), c = 7.89(5) Å, β = 112.2(5)°, Z = 2. The strongest lines in the powder X-ray diffraction pattern are 3.73 (15) (111), 3.31 (100) (112), 3.08 (20) (020), 3.00 (16) (301, 212, 102), 2.90 (19) (120), 2.80 (62) (121, 300), 2.16 (18) (321), 1.963 (15) (204). Electron microprobe analysis gave V2O5 31.77, SiO2 0.15, Al2O3 0.07, Fe2O3 2.33, Mn2O3 11.27, CaO 0.07, BaO 51.91, SrO 0.22, Na2O 0.13, H2O (calc.) 1.59, total 99.51 wt. %, and lead to the empirical formula, (Ba1.92Na0.02Sr0.01Ca0.01)Σ1.96(Mn3+0.81Fe3+0.17Al0.01)Σ0.99[(V1.99Si0.01)O7.92](OH)1.00 on the basis of V + Si = 2 and (OH) = 1. It is translucent and black red in color with a vitreous luster. The streak is dark brownish red and cleavage is not observed. The Mohs' hardness is about 4 to 4.5. The calculated density is 4.62 g/cm3. It has distinct pleochroism, from reddish orange to dark brownish red in thin section and the calculated mean refractive index is 2.03. It occurs as irregular grains under 15 μm, and the aggregates are up to 250 μm wide in association with braunite, hyalophane and tamaite. The mineral is formed under the later stage activity of low grade metamorphism.

著者

Kenji HORIE Tomokazu HOKADA Yoichi MOTOYOSHI Kazuyuki SHIRAISHI Yoshikuni HIROI Mami TAKEHARA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.111, no.2, pp.104-117, 2016 (Released:2016-05-05)

参考文献数

50

被引用文献数

2 10

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U–Pb zircon geochronology was applied to nine metasedimentary samples collected from Mt. Yuzhnaya, Condon Hills, and Mt. Lira in the inland region of the Rayner Complex of western Enderby Land, East Antarctica, in order to define the eastern limits of the western Rayner Complex that underwent the Pan–African metamorphism and to evaluate potential source areas of metasedimentary rocks. Condon Hills and Mt. Lira revealed metamorphic ages of ~ 894 and ~ 934 Ma, respectively, which are consistent with previously reported metamorphism in association with Rayner Structural Episode (RSE). Mt. Yuzhnaya samples affected by the RSE contain zircon grains rejuvenated during 590–570 Ma, which indicates that the Pan–African reworking can be extended up to Mt. Yuzhnaya. On the other hand, the Condon Hills samples include Archean detritus, and the age peaks from 3850 to 2491 Ma are the oldest components in the Rayner Complex of western Enderby Land. There is no evidence of reworked Napier Complex rocks in the studied Rayner samples.

著者

Hiroaki OHFUJI Masashi YAMAMOTO

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.110, no.4, pp.189-195, 2015 (Released:2015-08-29)

参考文献数

15

被引用文献数

1 15

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This study demonstrates the validity of a thin osmium coating for quantitative energy–dispersive spectroscopic (EDS) analysis, particularly for light elements such as O (and potentially C and N) in natural/synthetic minerals. An osmium coating prepared by chemical vapor deposition provides an extremely thin and uniform layer whose thickness can be controlled simply by coating time. Because of the high reproducibility and reliability of the osmium coating process, users have no difficulty in evaluating the actual coating thickness, which enables strict and precise absorption corrections (for the coating layer), even for low–energy characteristic X–rays, which are susceptible to attenuation by the coating layer itself. Our results show that oxygen concentrations in silicate and oxide minerals can be quantified correctly when using the osmium coating, whereas quantification using a carbon coating afforded values that were a few wt% lower than stoichiometry, probably due to the uncertainty of the actual coating thickness (i.e., the absorption correction was incorrect). The ability to accurately quantify oxygen may stimulate new analytical applications, such as the estimation of Fe2+/Fe3+ concentrations and water content in minerals. Furthermore, the Os–coated samples prepared for EDS analysis are also suitable for electron back–scattered diffraction (EBSD) analysis without re–polishing and re–coating, which are usually routine but time–consuming tasks in the case of carbon–coated samples.

著者

Tomoki NAKAMURA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.100, no.6, pp.260-272, 2005 (Released:2005-12-21)

参考文献数

61

被引用文献数

117 154

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The presence of abundant phyllosilicates in many carbonaceous chondrites indicates a prevailing activity of low-temperature aqueous alteration in primitive asteroids. However, among the hydrous carbonaceous chondrites known, more than 20 samples show evidence of having been heated at elevated temperatures with corresponding phyllosilicate dehydration. The mineralogical features of dehydration suggest that the heating occurred in situ in meteorites, which demonstrates that there are some hydrated asteroids that have been heated at a certain period after aqueous alteration. Recent studies have uncovered details of heating and dehydration processes in hydrous carbonaceous chondrites: step-by-step changes in mineralogy, trace element chemistry, carbonaceous materials, and reflectance spectra have been clarified. Based on data from synchrotron X-ray diffraction analysis of the matrix, heated hydrous carbonaceous chondrites have been classified as Stages I-IV, with the temperature of heating increasing from I to IV. In spite of recent progress, heat sources are poorly defined, mainly due to a lack of chronological information on the timing of the heating, and therefore more data are needed to fully clarify the thermal metamorphism of hydrous carbonaceous chondrites.

著者

Toshiro NAGASE Koichi MOMMA Takahiro KURIBAYASHI Masahiko TANAKA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.108, no.2, pp.87-93, 2013 (Released:2013-05-03)

参考文献数

21

被引用文献数

2

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Lutecite is an aggregate of microcrystalline silica; its variety with a hexagon form is known as hexalite. Textures of lutecite and hexalite from the Arz-Bord Range, in northwestern Gobi, Mongolia, and from Banyan-obo, China, were observed by optical microscopy, synchrotron X-ray diffraction, and transmission electron microscopy (TEM). Cross sections of lutecite and hexalite observed through optical microscopy show fibrous textures. TEM observations revealed that the quartz crystals constituting each fiber exhibit irregular shapes elongated parallel to [212], which is nearly perpendicular to (101); a width of 0.5 μm; and length of a few micrometers. The results of selected area electron diffraction analyses show that the fiber bundles have V-shaped cross textures, and the crystals are twinned according to the Reichenstein-Grieserntal law. X-ray diffraction analysis indicates a total moganite content of approximately 10 wt% in this lutecite aggregate, and moganite appears as irregular-shaped domains within quartz under high-resolution TEM.

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.107, no.3, pp.155-155, 2012 (Released:2012-07-12)

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The following are errata for the original article entitled “Epidote-Sr, CaSrAl2Fe3+(Si2O7)(SiO4)(OH), a new mineral from the Ananai mine, Kochi Prefecture, Japan” by Tetsuo MINAKAWA, Hiroyuki FUKUSHIMA, Daisuke NISHIO-HAMANE and Hiroyuki MIURA (Vol. 103, no. 6, 400-406, 2008). O is missing before (OH) by the authors' mistake.Title: CaSrAl2Fe3+(Si2O7)(SiO4)(OH) should be changed to CaSrAl2Fe3+(Si2O7)(SiO4)O(OH).Abstract, line 1: CaSrAl2Fe3+(Si2O7)(SiO4)(OH) should be changed to CaSrAl2Fe3+(Si2O7)(SiO4)O(OH).INTRODUCTION, line 2: A2M3 (T2O7)(TO4)(OH) should be changed to A2M3(T2O7)(TO4)O(OH).INTRODUCTION, line 9: Ca2Al2Fe3+(Si2O7)(SiO4)(OH) should be changed to Ca2Al2Fe3+(Si2O7)(SiO4)O(OH).INTRODUCTION, line 29: CaSrAl2Fe3+(Si2O7)(SiO4)(OH) should be changed to CaSrAl2Fe3+(Si2O7)(SiO4)O(OH).CHEMICAL PROPERTIES, line 26-27: CaSrAl2Fe3+(Si2O7)(SiO4)(OH) should be changed to CaSrAl2Fe3+(Si2O7)(SiO4)O(OH).The pattern of Serpentinite of Figure 1 on page 100 entitled “Finding of prehnite-pumpellyite facies metabasites from the Kurosegawa belt in Yatsushiro area, Kyushu, Japan” by Kenichiro KAMIMURA, Takao HIRAJIMA and Yoshiyuki FUJIMOTO (vol. 107, no. 2, 99-104, 2012) is missing. Below is the corrected Figure 1. The Printer apologizes for the misprint.

著者

Kenichiro KAMIMURA Takao HIRAJIMA Yoshiyuki FUJIMOTO

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.1204050196-1204050196, (Released:2012-04-07)

被引用文献数

1 5

著者

Ushio HONMA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.107, no.1, pp.8-32, 2012 (Released:2012-02-29)

参考文献数

50

被引用文献数

3 3

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It has been well established that the exchange partition coefficient for the exchange of Ca and Na between plagioclase and silicate melts [Kd = (Ca/Na)pl/(Ca/Na)melt] increases with increasing water content in the melt, but its atomistic interpretation is not well developed. This work presents new experimental data on the partition coefficient in an alkali basalt and a transitional tholeiite from the Oginosen volcano, southwest Japan and discusses the possible role of melt polymerization in the variations of the partition coefficient. The experiments were conducted at 0.1 MPa, and hydrous 100 MPa and 200 MPa conditions. The partition coefficient at 0.1 MPa increases from 0.8-1.4 to 1.5-1.8 over a temperature increase from 1090 °C to 1190 °C in the transitional tholeiite, and from 1.2 to 1.7 for 1090 °C to 1150 °C in the alkali basalt. The partition coefficient increases up to 4.1-4.2 in the presence of 3.4-3.5 wt% water in the melt in both basalts. The variations of the Ca-Na partition coefficient between the plagioclase and the melt is interpreted in terms of the degree of polymerization of the melt. The degree of polymerization of the melt decreases with the increase of temperature and water content, both of which increase the Ca-Na partition coefficient.   The anorthite content of the core of natural plagioclase phenocrysts in the alkali basalt is 63-66 mol%, suggesting crystallization under water-undersaturated conditions. In the transitional tholeiite, some of the cores of the plagioclase phenocrysts have An81-85, which is formed in a water-supersaturated run at 100 MPa and 1085 °C; however, the significance of the presence of An81-85 is unknown and must be investigated further.

著者

Kenta YOSHIDA Takao HIRAJIMA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.1202160190, (Released:2012-02-18)

被引用文献数

5 5

著者

Kenta YOSHIDA Yoshiteru SENGEN Shigeki TSUCHIYA Kouta MINAGAWA Tomoyuki KOBAYASHI Taketoshi MISHIMA Shinji OHSAWA Takao HIRAJIMA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.106, no.3, pp.164-168, 2011 (Released:2011-07-05)

参考文献数

26

被引用文献数

5 5

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A remarkably high Li/B ratio has been recognized from a crush-leached fluid extracted from a foliation-parallel quartz vein, IR27, intercalated with a pelitic schist in the northern proximal to the Western Iratsu body of the Sambagawa metamorphic belt, SW Japan. Thin section observation shows that most quartz grains in the vein are polygonal and rarely show the undulatory extinction. These facts suggest that the quartz grains in the vein could be recrystallized under relatively high-T condition with the stress free environment, and that these fluid inclusions could be trapped during the peak metamorphic stage. Most fluid inclusions in the investigated sample are composed of liquid and vapor. Raman spectroscopy revealed that the liquid phase is aqueous fluid and the vapor is mainly a mixture of CH4 and N2. Their ice melting temperatures determined by microthermometry, ranging from -3.5 to -7.1 °C, show a striking contrast against the data of the fluid inclusions in later stage veins, ranging from -0.6 to -1.7 °C. However, the homogenization temperatures of IR27 are much lower than the peak metamorphic temperature of the host pelitic schist. The partition coefficients between the host rock and released fluid (Drock/fluid) calculated from P-T pseudosection show that DBrock/fluid tends to be higher than DLirock/fluid in a pelitic system, because of generally high modes of white mica in pelitic schists. The calculation suggests that the crush-leached fluid obtained from the quartz vein intercalated with the pelitic schist has higher Li/B ratio than fluids of those intercalated with the metabasite.

著者

HORI Hidemichi KOBAYASHI Toshinori MIYAWAKI Ritsuro MATSUBARA Satoshi YOKOYAMA Kazumi SHIMIZU Masaaki

出版者

日本鉱物科学会

雑誌

Journal of mineralogical and petrological sciences (ISSN:13456296)

巻号頁・発行日

vol.101, no.4, pp.170-177, 2006-08-01

被引用文献数

1 8

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Iwashiroite-(Y), YTaO₄, was found from Suishoyama, Kawamata Town, Fukushima Prefecture, Japan. It is monoclinic</i>, <i>P</i>2/<i>a</i>, <i>a</i> = 5.262(5) Å, <i>b</i> = 5.451(5) Å, <i>c</i> = 5.110(5) Å, β = 95.12(10)°, <i>V</i> = 146.0(2) ų, Z = 2. The five strongest lines in the powder XRD pattern [<i>d</i>(Å), <i>I</i>/<i>I</i>₀, <i>hkl</i>] are (3.13, 100, 111), (2.95, 94, 111), (2.73, 26, 020), (1.890, 29, 220) and (1.862, 29, 022). Electron microprobe analysis gave; Y₂O₃ 29.10, Ce₂O₃ 0.10, Nd₂O₃ 0.10, Sm₂O₃ 0.36, Gd₂O₃ 1.06, Tb₂O₃ 0.25, Dy₂O₃ 2.38, Ho₂O₃ 0.56, Er₂O₃ 2.09, Tm₂O₃ 0.37, Yb₂O₃ 3.33, Lu₂O₃ 0.85, ThO₂ 0.02, UO₂ 0.15, CaO 0.17, Ta₂O₅ 40.64, Nb₂O₅ 16.66, TiO₂ 0.41, total 98.60 wt%, and leads to the empirical formula, (Y_0.81Yb_0.05Dy_0.04Er_0.03</sub>Gd_0.02Lu_0.01Ho_0.01Sm_0.01Ca_0.01Tm_0.01)_Σ1.00(Ta_0.58Nb_0.39T_i0.02)_Σ0.99O₄ on the basis of the 4 oxygen atoms per formula unit. Iwashiroite-(Y) is translucent and amber brown to brown in color with a glassy to subadamantine luster. The streak is pale brown and cleavage is {010} good, {001} poor. The Mohs' hardness is 6. The calculated density is 7.1 g/cm³. Iwashiroite-(Y) occurs as an aggregate of small euhedral platy crystals with a metamict substance in the main ore body of the granite pegmatite mine at the locality. Associated minerals are quartz, microcline and annite. The crystal structure was refined to <i>R</i> = 0.034 with single crystal XRD data. Although the structure consists of TaO₆ octahedra and YO₈ polyhedra, iwashiroite-(Y) is not isostructural with fergusonite-beta-(Y).

著者

Hidemichi HORI Toshinori Kobayashi Ritsuro MIYAWAKI Satoshi MATSUBARA Kazumi YOKOYAMA Masaaki SHIMIZU

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.101, no.4, pp.170-177, 2006 (Released:2006-08-08)

参考文献数

23

被引用文献数

4 8

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Iwashiroite-(Y), YTaO4, was found from Suishoyama, Kawamata Town, Fukushima Prefecture, Japan. It is monoclinic, P2/a, a = 5.262(5) Å, b = 5.451(5) Å, c = 5.110(5) Å, β = 95.12(10)°, V = 146.0(2) Å3, Z = 2. The five strongest lines in the powder XRD pattern [d(Å), I/I0, hkl] are (3.13, 100, 111), (2.95, 94, 111), (2.73, 26, 020), (1.890, 29, 220) and (1.862, 29, 022). Electron microprobe analysis gave; Y2O3 29.10, Ce2O3 0.10, Nd2O3 0.10, Sm2O3 0.36, Gd2O3 1.06, Tb2O3 0.25, Dy2O3 2.38, Ho2O3 0.56, Er2O3 2.09, Tm2O3 0.37, Yb2O3 3.33, Lu2O3 0.85, ThO2 0.02, UO2 0.15, CaO 0.17, Ta2O5 40.64, Nb2O5 16.66, TiO2 0.41, total 98.60 wt%, and leads to the empirical formula, (Y0.81Yb0.05Dy0.04Er0.03Gd0.02Lu0.01Ho0.01Sm0.01Ca0.01Tm0.01)Σ1.00(Ta0.58Nb0.39Ti0.02)Σ0.99O4 on the basis of the 4 oxygen atoms per formula unit. Iwashiroite-(Y) is translucent and amber brown to brown in color with a glassy to subadamantine luster. The streak is pale brown and cleavage is {010} good, {001} poor. The Mohs' hardness is 6. The calculated density is 7.1 g/cm3. Iwashiroite-(Y) occurs as an aggregate of small euhedral platy crystals with a metamict substance in the main ore body of the granite pegmatite mine at the locality. Associated minerals are quartz, microcline and annite. The crystal structure was refined to R = 0.034 with single crystal XRD data. Although the structure consists of TaO6 octahedra and YO8 polyhedra, iwashiroite-(Y) is not isostructural with fergusonite-beta-(Y).