2026 年 121 巻 1 号 論文ID: 260301
Horiite is a new member of the bafertisite group within the seidozerite supergroup, discovered at the Taguchi mine in Aichi Prefecture, Japan. The mineral was named in honor of Dr. Hidemichi Hori (1934-2019), a distinguished Japanese mineralogist and founder of Hori Mineralogy, Ltd. Horiite crystals are thin, elongated plates with long axes up to 300 µm in length and 20 µm in thickness. They are closely layered and tend to aggregate, sometimes forming aggregates with hejtmanite. The Mohs hardness of horiite is 4-5, its tenacity is brittle, and its calculated density is 4.08 g·cm−3. Under plane-polarized light, the mineral shows very weak pleochroism, changing from nearly colorless to pale brown. The empirical formula, calculated on the basis of 24 O and 2 (OH + F) atoms per formula unit, is (Ba1.98Sr0.01)Σ1.99(Mn1.97Ca0.04)Σ2.01(Mn3.34Fe0.36Mg0.31)Σ4.01(Ti1.98Sn0.03)Σ2.01Si4.00P1.99O24[(OH)1.92F0.08]Σ2, ideally Ba2Mn2Mn4Ti2(Si2O7)2(PO4)2O2(OH)2. The refined unit-cell parameters determined by single-crystal X-ray diffraction are a = 5.35090(10) Å, b = 13.89170(10) Å, c = 14.2777(2) Å, α = 98.7260(10)°, β = 93.8420(10)°, γ = 90.0570(10)°, and V = 1046.60(3) Å3, and Z = 2, in conjunction with space group P1 (#2), whereas the lattice parameters determined by synchrotron-radiation powder X-ray diffraction are a = 5.3349(9) Å, b = 13.884(2) Å, c = 14.270(3) Å, α = 98.785(15)°, β = 93.836(16)°, γ = 90.029(16)°, and V = 1043.7(3) Å3. Although the crystal structure of horiite is partially related to that of yoshimuraite, it represents a new structural type. Consequently, according to the nomenclature concept of the seidozerite supergroup, the crystal structure of horiite is identified as the fifth basic structure within the bafertisite group. Horiite is the only species among more than 50 in the seidozerite supergroup that contains species defining Mn-occupied sites in the I block.
Titanium-silicate (TS) block minerals, known for their complex chemical compositions and structures, have been systematized under the seidozerite supergroup by Sokolova and Cámara (2017). Within this supergroup, minerals are classified into four groups on the basis of their Ti content in atoms per formula unit (apfu) per (Si2O7)2 in the TS block: the rinkite group (Ti = 1 apfu), bafertisite group (Ti = 2 apfu), lamprophyllite group (Ti = 3 apfu), and the murmanite group (Ti = 4 apfu). Their structures are a combination of a TS block consisting of octahedral (O) and heteropolyhedral (H) sheets and an intermediate (I) block (Sokolova and Cámara, 2017).
To date, eight mineral species have been identified in the bafertisite group. In Japan, two members of the bafertisite group, yoshimuraite and hejtmanite, have been collected from several localities, and both species were confirmed to occur at the Taguchi mine in Aichi Prefecture (Hirowatari and Isono, 1963; Hori et al., 1985). Yoshimuraite was first structurally characterized using a specimen from the Taguchi mine (McDonald et al., 2000). However, hejtmanite from the Taguchi mine has thus far only been described as a Mn-analogue of bafertisite (Hori et al., 1985); no identification based on crystal structure analysis has been reported. In the course of our detailed investigation of the so-called ‘hejtmanite’ from the Taguchi mine, we discovered a new mineral species belonging to the bafertisite group, distinct from both yoshimuraite and hejtmanite.
The new mineral has been named horiite in honor of Dr. Hidemichi Hori (1934-2019), a distinguished Japanese mineralogist affiliated with Hori Mineralogy, Ltd. He made significant contributions to descriptive mineralogy, having been involved in the discovery of five new mineral species: kinichilite, stronalsite, ammonioleucite, iwashiroite-(Y), and tanohataite. Beyond his scientific work, Dr. Hori was passionate about sharing the beauty and value of minerals with the public. In 1986, he founded Friends of Mineral Tokyo, an amateur mineral club dedicated to promoting mineral education and awareness in Japan. Through his numerous publications aimed at general readers, he inspired and mentored a generation of mineralogists, both directly and indirectly. In recognition of his lifelong contributions to mineralogy and public outreach, the new mineral horiite is named in his honor.
The mineral and its name of horiite (IMA No. 2025-029) have been approved by the International Mineralogical Association, Commission on New Minerals, Nomenclature, and Classification. The holotype specimen has been deposited in the collection of the National Museum of Nature and Science, Japan (NSM-M53164).
Horiite was found at the Taguchi mine, located in Yatsuhashi, Shitara Town, Aichi Prefecture, Japan (35°08′31.2′′N, 137°35′24.1′′E). According to previous studies (e.g., Yamaguchi and Hirowatari, 1969; Yoshimura, 1969; Ishida et al., 2004), the Taguchi mine is a manganese deposit associated with pelitic gneiss within the Ryoke metamorphic belt. The deposit has undergone low P/T-type regional metamorphism of Cretaceous age and was thereafter thermally metamorphosed by an adjacent granodiorite. In the deposit, pegmatite and aplite dikes have also been noted in previous studies. The Rb-Sr ages of manganese ores containing yoshimuraite range from 71 to 80 Ma (Yamaguchi and Hirowatari, 1969).
The manganese ore is siliceous and primarily composed of rhodonite, pyroxmangite, and tephroite. Notably, yoshimuraite has been reported in coarse-grained ore dominated by rhodonite and amphibole (Hirowatari and Isono, 1963; Yamaguchi and Hirowatari, 1969). This amphibole was originally reported as richterite (Shoda and Bunno, 1973); however, its composition corresponds to hjalmarite, an amphibole species recently described by Holtstam et al. (2019). Yoshimuraite also occurs within rhodonite aggregates without any associated amphibole. A Mn-dominant bafertisite from the coarse-grained ore dominated by rhodonite was subsequently reported (Hori et al., 1985), and this mineral is now considered to correspond to hejtmanite. In the present study, however, we have identified horiite that resembles hejtmanite in appearance.
Figure 1 shows a representative occurrence of horiite and other species (hejtmanite and yoshimuraite) for comparison. Specimens of horiite occur as pale-ochre aggregates of tabular crystals arranged in parallel—an appearance that closely resembles that of hejtmanite (Figs. 1a and 1b). By contrast, yoshimuraite exhibits a darker-brown color and tends to form broader tabular crystals (Fig. 1c), giving it a distinctly different appearance from the other two (Figs. 1a and 1b). Horiite is invariably closely associated with quartz, in which its crystals are embedded. The individual crystals of horiite are thin and elongated, exhibiting a platy habit, and can reach more than 300 µm in length, approximately 100 µm in width, and approximately 20 µm in thickness (Fig. 2). Horiite is commonly associated with pyrophanite, fluorapatite, celsian, K-feldspar, and phlogopite. Except for pyrophanite and phlogopite, these associated minerals are colorless and transparent, making them difficult to recognize visually. Their presence is typically revealed through observations under an optical microscope or a scanning electron microscope. In some cases, horiite and hejtmanite form a micrometer-scale layered aggregate that incorporates these associated minerals (Fig. 3). Although the proportions of the two minerals in the layered aggregate can vary considerably, and irrespective of whether they occur as single phases or as intergrowths, they consistently exhibit a similar external appearance.
Horiite is pale ochre with a white streak and exhibits a vitreous luster. It is translucent and exhibits no fluorescence. Its Mohs hardness is estimated to be 4-5 on the basis of a test where reference powder was rubbed against a thin crystal mounted onto a glass slide. The mineral shows perfect cleavage on the {001} plane, with no observed parting. It is brittle in tenacity and displays an uneven fracture. The measured density could not be determined because it exceeds the density of the available heavy liquid; however, the density calculated on the basis of the empirical formula and single-crystal X-ray diffraction (XRD) data is 4.08 g·cm−3.
Horiite is optically biaxial (+) with refractive indexes of α = 1.772(2), β = 1.782(2), and γ > 1.81 (white light) using available media (methylene iodide + sulfur + tetraiodoethylene) and exhibits weak pleochroism. Because of the lack of suitable equipment, the 2V value and orientation could not be obtained directly. Birefringence could also not be measured. The mean refractive index obtained from the Gladstone-Dale relationship (Mandarino, 1981) using the empirical formula and calculated density is 1.837. The pleochroism is very weak, involving a change from nearly colorless to pale brown.
Raman spectroscopy for horiite was conducted with a Renishaw inVia Reflex spectrometer using a green diode laser with an excitation wavelength of λ = 532 nm at the Institute for Solid State Physics of the University of Tokyo (ISSP). The laser power at the sample surface was approximately 10 mW. Figure 4 shows the Raman spectrum. For comparison, the Raman spectra of yoshimuraite and hejtmanite obtained from the same locality are also shown. The raw data for each is deposited as Supplementary Documents (Supplementary Documents are available online from https://doi.org/10.2465/jmps.260301).
The peak at ∼ 3600 cm−1 is assigned to OH-stretching vibrations of the OH groups. In horiite, these vibrations appear as a single band, likely because the two OH groups occupy nearly equivalent positions, causing their corresponding peaks to overlap. In contrast, multiple bands are observed in yoshimuraite and hejtmanite. Commonly, even when only one type of OH group is present, cation substitutions (solid solution) affecting the donor and/or acceptor oxygen can modify local bond distances, often resulting in multiple bands derived from a single OH group. Yoshimuraite and hejtmanite likely exhibit solid solution with respect to cation composition or OH-F content (Supplementary Table S1; Tables S1-S4 are available online from https://doi.org/10.2465/jmps.260301). At present, however, it remains difficult to discuss in detail the differences in OH-stretching vibrations among yoshimuraite, hejtmanite, and horiite, and a more comprehensive analysis will be required in future studies.
On the basis of the literature data for related TS-block minerals (e.g., Sokolova et al., 2015a), bands at wavenumbers greater than 800 cm−1 can be assigned to Si-O stretching vibrations, whereas those at wavenumbers less than 800 cm−1 correspond to Si-O bending and M-O modes. In addition, the spectra are further complicated by the presence of PO4 tetrahedra in the I block; the vibrational modes of PO4 tetrahedra typically appear as intense signals at wavenumbers greater than 900 cm−1. On the other hand, it is difficult to make specific assignments for the peaks observed in horiite, yoshimuraite, and hejtmanite.
Chemical analyses of the type specimen of horiite were carried out using a JEOL JXA-8230 electron microprobe (WDS mode, 15 kV, 20 nA, and 1 µm beam diameter) at Yamaguchi University. The ZAF method was used for data correction. Although insufficient pure material was available for direct determination, single-crystal X-ray refinement indicated the presence of OH in the structure (also confirmed by Raman spectroscopy). Thus, the H2O wt% was estimated from stoichiometry.
Horiite in the type specimen is compositionally homogeneous, and the analytical data are given in Table 1. The empirical formula of horiite, calculated on the basis of 24 O and 2 (OH + F) apfu, is (Ba1.98Sr0.01)Σ1.99(Mn1.97Ca0.04)Σ2.01(Mn3.34Fe0.36Mg0.31)Σ4.01(Ti1.98Sn0.03)Σ2.01Si4.00P1.99O24[(OH)1.92F0.08]Σ2. The ideal formula is Ba2Mn2Mn4Ti2(Si2O7)2(PO4)2O2(OH)2, which requires BaO 23.73, MnO 32.93, TiO2 12.36, SiO2 18.60, P2O5 10.98, H2O 1.39, total 100 wt%.
| wt% (n = 42) | apfu | |||||
| Avg. | Range | Stand. Dev. | Standard | Ba | 1.98 | |
| BaO | 23.50 | 23.11-23.98 | 0.23 | BaSO4 | Sr | 0.01 |
| SrO | 0.05 | 0-0.10 | 0.03 | SrBaNb4O12 | Σ | 1.99 |
| MnO | 29.13 | 28.47-29.49 | 0.23 | MnO | ||
| CaO | 0.15 | 0.08-0.35 | 0.06 | CaSiO3 | Mn | 1.97 |
| FeO | 2.01 | 1.74-2.38 | 0.18 | Fe2O3 | Ca | 0.04 |
| MgO | 0.96 | 0.66-1.15 | 0.12 | MgO | Σ | 2.01 |
| TiO2 | 12.23 | 11.95-12.48 | 0.13 | TiO2 | ||
| SnO2 | 0.32 | 0.14-0.60 | 0.11 | SnO2 | Mn | 3.34 |
| SiO2 | 18.54 | 18.15-18.84 | 0.13 | CaSiO3 | Fe | 0.36 |
| P2O5 | 10.89 | 10.52-11.05 | 0.11 | KTiPO5 | Mg | 0.31 |
| SO3 | 0.00 | 0-0.02 | 0.01 | BaSO4 | Σ | 4.01 |
| F | 0.12 | 0-0.44 | 0.12 | |||
| H2O* | 1.33 | Ti | 1.98 | |||
| -O=F | 0.05 | Sn | 0.03 | |||
| Total | 99.18 | Σ | 2.01 | |||
| Si | 4.00 | |||||
| P | 1.99 | |||||
| O = | 24 | |||||
| OH | 1.92 | |||||
| F | 0.08 | |||||
| Σ = | 2 | |||||
* Calculated value as OH + F = 2.
The chemical compositions of yoshimuraite and hejtmanite are given in Table S1. The Mn:Fe:Mg ratios at the octahedral sites and the content in Ti site are nearly identical for horiite and hejtmanite, whereas yoshimuraite is enriched in Fe compared to the other two.
Minerals of the seidozerite supergroup often exhibit some structural defects that can hinder crystal-structure analysis (e.g., Sokolova and Cámara, 2017). In the present study, we used transmission electron microscopy (TEM) to examine the quality of the crystals used for X-ray XRD work. Samples were prepared from crystals of the type specimen using Ar+-ion milling with an ion-slicer (JEOL EM-09100IS). TEM observations were conducted at 200 kV using a JEOL JEM-2100 at ISSP.
Selected-area electron diffraction patterns are shown in Figures 5a and 5b. Weak streaks are occasionally observed along the c*-axis, corresponding to the stacking direction of the TS blocks (Fig. 5b). In fact, defects can be observed in the high-resolution image. For example, although the (001) spacing for horiite is approximately 14 Å, a spacing of approximately 28 Å is occasionally observed (Fig. 5c). However, such areas are sparse throughout the crystal (Fig. 5d). Therefore, we determined that the single crystal of horiite obtained from the type specimen was suitable for crystal structure analysis.
The factors (i.e., intergrowth of other phases, polytypes, or twins) that account for the irregular periods in the horiite crystal are unclear, although a likely possibility is a derivative structure consisting of two basic structures. For example, the structure of cámaraite is a derivative structure combining the basic structures of bafertisite and jinshajiangite; as a result, the c-axis length for cámaraite is approximately twice as long as those for the basic structures. In addition, a known example of the intergrowth of cámaraite and bafertisite has already been reported (e.g., Cámara et al., 2009). Sokolova and Cámara (2013) subsequently discussed several possible derivative structures in the bafertisite group; however, the horiite-based structure was not included among those predicted derivative structures because it is a new basic structure (discussed later).
Single-crystal X-ray diffractionXRD data for a single crystal of horiite were collected with MoKα radiation using an XtaLAB Synergy-R/DW equipped with VariMax DW optics and a HyPix6000HE detector (Rigaku), located at the Center for Instrumental Analysis, Yamaguchi University. The crystal sample was mounted onto a glass fiber, and intensity data were collected at room temperature. Preliminary unit-cell parameters and an orientation matrix were obtained from six sets of frames and were refined during the integration process for the intensity data. Diffraction data and empirical absorption correction were performed using CrysAlisPro (Agilent, 2014). The initial structure model was obtained using the charge-flipping method with the olex2.solve (Dolomanov et al., 2009) structure solution program incorporating the algorithm by Oszlányi and Sütő (2008). Subsequent structure completion and refinement were performed by full-matrix least-squares methods on F2 using SHELXL-2019/2 (Sheldrick, 2015). All non-hydrogen atoms were located through successive difference Fourier syntheses and refined with anisotropic displacement parameters. During the refinement process, Mn and Mg were considered to occupy the Mn1-Mn5 sites. In this operation, the trace amounts of Fe are treated as Mn because they share almost the same X-ray scattering parameters. As a result, the Mn/Mg ratio was consistent with the WDS analysis. The hydrogen positions of the hydroxyl groups were derived from difference-Fourier synthesis, and the displacement parameter for the H atom was fixed at Uiso = 0.05 Å2, with a restraint of O-H = 0.980(1) Å applied (Franks, 1973). In the refined structural formula, the O atoms at the O23 and O26 sites form the hydroxyl groups as O23-H23 and O26-H26.
CheckCIF reported level B and level C alerts around the Ba and O sites, which were likely due to small defects such as those observed by TEM (Fig. 5). However, alerts of these magnitudes do not compromise the reliability of the crystal structure analysis. Indeed, the structural analysis converged with sufficient accuracy to construct a crystal structure model (Rint = 2.47%, R1 = 3.03%).
Details of the sample, data collection, and structure refinement are provided in Table 2 and Supplementary CIF file (Supplementary CIF file is available online from https://doi.org/10.2465/jmps.260301). The final atom positions and selected interatomic distances are shown in Table 3 and Table 4, respectively. The detailed displacement parameters and the calculated bond valences based on Gagné and Hawthorne (2015) are summarized in Table S2 and Table S3, respectively. The refined unit-cell parameters were a = 5.35090(10) Å, b = 13.89170(10) Å, c = 14.2777(2) Å, α = 98.7260(10)°, β = 93.8420(10)°, γ = 90.0570(10)°, and V = 1046.60(3) Å3, and Z = 2, in conjunction with space group P$\bar{1}$ (#2).
| Crystal size (mm) | 0.10 × 0.08 × 0.02 | |
| Space group | P$\bar{1}$ | |
| Unit-cell dimensions |
a, b, c (Å) | 5.35090(10), 13.89170(10), 14.2777(2) |
| α, β, γ (°) | 98.7260(10), 93.8420(10), 90.0570(10) | |
| V (Å3) | 1046.60(3) | |
| Dcalc (g·cm−3) | 4.07 | |
| Radiation | MoKα (λ = 0.71073 Å) | |
| Monochromator | VariMax DW optics | |
| Diffractometer | Rigaku XtaLAB Synergy-R/DW with HyPix6000HE |
|
| Scan type | ω scan | |
| Absorption correction | CrysAlisPro (Agilent, 2014) | |
| Absorption coefficient μ (mm−1) |
8.26 | |
| θmin-θmax (°) | 2.9-40.8 | |
| Collected reflections | 66196 | |
| Unique reflections with I > 2σ (I) |
11077 | |
| Rint (%) | 2.47 | |
| Index ranges | h | −9 → 9 |
| k | −25 → 25 | |
| l | −25 → 26 | |
| Refinement on F2 using | SHELXL-2019/2 (Sheldrick, 2015) | |
| R1 (%) | 3.03 | |
| wR2 (%) | 8.08 | |
| No. of parameters | 393 | |
| Goodness of fit (S) | 1.13 | |
| Weighting scheme* | w = 1/[σ2(Fo2) + (0.0254P)2 + 4.7739P] | |
| Δρmax (e Å−3) | 3.089 | |
| Δρmin (e Å−3) | −1.887 | |
* The function of the weighting scheme is w = 1/[σ2(Fo2) + (a·P)2 + b·P], where P = [Max(Fo2) + 2Fc2]/3, and the parameters a and b are chosen to minimize the differences in the variances for reflections in different ranges of intensity and diffraction angle.
| Formula notation* | Site | x | y | z | Uiso*/Ueq | s.o. |
| Ap | Ba1 | 0.79859(3) | 0.84660(2) | 0.62008(2) | 0.01304(3) | Ba1.0 |
| Ap | Ba2 | 0.74392(3) | 0.34679(2) | 0.62013(2) | 0.01305(3) | Ba1.0 |
| Bp | Mn6 | 0.75721(7) | 0.90853(3) | 0.36635(3) | 0.01145(6) | Mn1.0 |
| Bp | Mn7 | 0.69393(7) | 0.40817(3) | 0.36618(3) | 0.01128(6) | Mn1.0 |
| Mo | Mn1 | 0 | 0 | 0 | 0.01151(15) | Mn0.949Mg0.051(7) |
| Mo | Mn2 | 0.50215(6) | 0.87663(3) | 0.00917(3) | 0.00835(10) | Mn0.939Mg0.061(5) |
| Mo | Mn3 | 0.00200(7) | 0.75030(3) | 0.99837(3) | 0.01084(11) | Mn0.898Mg0.102(5) |
| Mo | Mn4 | 0.50115(6) | 0.62369(3) | 0.99264(3) | 0.00844(10) | Mn0.928Mg0.072(5) |
| Mo | Mn5 | 0 | 0.5 | 0 | 0.01272(15) | Mn0.947Mg0.053(7) |
| MH | Ti1 | 0.79911(6) | 0.08941(3) | 0.78054(3) | 0.00551(5) | Ti1.0 |
| MH | Ti2 | 0.79954(6) | 0.58938(3) | 0.78030(3) | 0.00564(5) | Ti1.0 |
| Si | Si1 | 0.67902(11) | 0.04592(4) | 0.19339(4) | 0.00608(9) | Si1.0 |
| Si | Si2 | 0.68130(11) | 0.26487(4) | 0.19375(4) | 0.00631(9) | Si1.0 |
| Si | Si3 | 0.71272(11) | 0.54569(4) | 0.19303(4) | 0.00590(9) | Si1.0 |
| Si | Si4 | 0.71027(11) | 0.76508(4) | 0.19329(4) | 0.00616(9) | Si1.0 |
| T | P1 | 0.74230(11) | 0.10496(4) | 0.54043(4) | 0.00776(8) | P1.0 |
| T | P2 | 0.77287(11) | 0.60468(4) | 0.54027(4) | 0.00783(8) | P1.0 |
| O | O1 | 0.8954(3) | 0.98681(12) | 0.24406(13) | 0.0096(2) | O1.0 |
| O | O2 | 0.5973(3) | 0.96839(12) | 0.77019(13) | 0.0099(2) | O1.0 |
| O | O3 | 0.6742(3) | 0.01785(12) | 0.07814(12) | 0.0086(2) | O1.0 |
| O | O4 | 0.7618(3) | 0.16073(12) | 0.22653(13) | 0.0102(3) | O1.0 |
| O | O5 | 0.4178(3) | 0.29759(13) | 0.23924(13) | 0.0107(3) | O1.0 |
| O | O6 | 0.6684(3) | 0.25691(12) | 0.07897(12) | 0.0086(2) | O1.0 |
| O | O7 | 0.8999(3) | 0.34091(12) | 0.24353(13) | 0.0098(2) | O1.0 |
| O | O8 | 0.4846(3) | 0.51319(12) | 0.75562(13) | 0.0097(2) | O1.0 |
| O | O9 | 0.0017(3) | 0.53176(12) | 0.22883(12) | 0.0090(2) | O1.0 |
| O | O10 | 0.6751(3) | 0.51750(12) | 0.07785(12) | 0.0088(2) | O1.0 |
| O | O11 | 0.6394(3) | 0.66031(12) | 0.22535(13) | 0.0102(3) | O1.0 |
| O | O12 | 0.6798(3) | 0.75758(12) | 0.07862(12) | 0.0088(2) | O1.0 |
| O | O13 | 0.9904(3) | 0.79678(12) | 0.23800(13) | 0.0104(3) | O1.0 |
| O | O14 | 0.5112(3) | 0.84124(12) | 0.24394(12) | 0.0092(2) | O1.0 |
| O | O15 | 0.7325(4) | 0.04650(15) | 0.44096(14) | 0.0179(3) | O1.0 |
| O | O16 | 0.4991(3) | 0.83568(13) | 0.44692(14) | 0.0122(3) | O1.0 |
| O | O17 | 0.9761(3) | 0.17200(13) | 0.55222(14) | 0.0125(3) | O1.0 |
| O | O18 | 0.7483(4) | 0.54615(15) | 0.44090(14) | 0.0175(3) | O1.0 |
| O | O19 | 0.5430(3) | 0.67202(14) | 0.55149(14) | 0.0127(3) | O1.0 |
| O | O20 | 0.0184(3) | 0.66406(13) | 0.55317(14) | 0.0122(3) | O1.0 |
| XOM | XOM1 | 0.8191(3) | 0.11193(12) | 0.90770(12) | 0.0097(2) | O1.0 |
| XOM | XOM2 | 0.8168(3) | 0.61211(13) | 0.90715(12) | 0.0100(2) | O1.0 |
| XOA | XOA1 | 0.8313(3) | 0.86498(13) | 0.93359(13) | 0.0108(3) | O1.0 |
| H1 | 0.823(12) | 0.861(5) | 0.8644(5) | 0.050* | H1.0 | |
| XOA | XOA2 | 0.8306(3) | 0.36385(13) | 0.93483(12) | 0.0105(3) | O1.0 |
| H2 | 0.824(12) | 0.357(5) | 0.8654(3) | 0.050* | H1.0 | |
| XPM | XPM1 | 0.7740(3) | 0.04217(13) | 0.62102(13) | 0.0117(3) | O1.0 |
| XPM | XPM2 | 0.7685(4) | 0.54205(13) | 0.62099(13) | 0.0118(3) | O1.0 |
* The general formula of horiite structure can be written as AP2BP2MO4MH2(Si2O7)2(TO3XPM)2(XOM)2(XOA)2.
| TSblock | Iblock | ||||||
| Ti1-O1 | 1.9708(17) | Mn1-O3 | 2.1267(17)×2 | P1-O15 | 1.523(2) | Ba1-O1 | 3.1629(16) |
| Ti1-O2 | 1.9784(17) | Mn1-XOM1 | 2.3548(18)×2 | P1-O16 | 1.5393(18) | Ba1-O2 | 2.7980(18) |
| Ti1-O13 | 2.0004(18) | Mn1-XOA1 | 2.1388(17)×2 | P1-O17 | 1.5436(18) | Ba1-O4 | 3.1173(17) |
| Ti1-O14 | 1.9583(17) | Average | 2.207 | P1-XPM1 | 1.547(3) | Ba1-O5 | 3.304(2) |
| Ti1-XOM1 | 1.7908(18) | BVS | 1.99 | Average | 1.538 | Ba1-O15 | 3.153(3) |
| Ti1-XPM1 | 2.2675(19) | BVS | 4.96 | Ba1-O15′ | 3.333(3) | ||
| Average | 1.994 | Mn2-O3 | 2.2259(17) | Ba1-O16 | 2.8387(19) | ||
| BVS | 3.88 | Mn2-O3′ | 2.2344(19) | P2-O18 | 1.522(2) | Ba1-O17 | 2.789(2) |
| Mn2-O6 | 2.2343(16) | P2-O19 | 1.5482(19) | Ba1-O19 | 2.7936(19) | ||
| Ti2-O5 | 1.9972(19) | Mn2-O12 | 2.2352(18) | P2-O20 | 1.5362(18) | Ba1-O20 | 2.8544(18) |
| Ti2-O7 | 1.9520(18) | Mn2-XOM1 | 2.1461(18) | P2-XPM2 | 1.547(3) | Ba1-XPM1 | 2.7182(19) |
| Ti2-O8 | 1.9718(17) | Mn2-XOA1 | 2.1201(18) | Average | 1.538 | Average | 2.914 |
| Ti2-O9 | 1.9838(17) | Average | 2.199 | BVS | 4.96 | BVS | 1.91 |
| Ti2-XOM2 | 1.7867(18) | BVS | 1.98 | ||||
| Ti2-XPM2 | 2.2647(19) | Ba2-O8 | 3.1655(17) | ||||
| Average | 1.993 | Mn3-O6 | 2.1372(18) | Ba2-O9 | 2.8014(16) | ||
| BVS | 3.90 | Mn3-O12 | 2.1273(18) | Ba2-O11 | 3.1235(19) | ||
| Mn3-XOM1 | 2.3288(16) | Ba2-O13 | 3.3087(19) | ||||
| Si1-O1 | 1.6150(19) | Mn3-XOM2 | 2.3298(17) | Ba2-O16 | 2.8501(18) | ||
| Si1-O2 | 1.6217(19) | Mn3-XOA1 | 2.136(2) | Ba2-O17 | 2.7987(18) | ||
| Si1-O3 | 1.6310(18) | Mn3-XOA2 | 2.1386(19) | Ba2-O18 | 3.163(3) | ||
| Si1-O4 | 1.6448(17) | Average | 2.200 | Ba2-O18′ | 3.325(3) | ||
| Average | 1.628 | BVS | 1.99 | Ba2-O19 | 2.7803(19) | ||
| BVS | 3.96 | Ba2-O20 | 2.841(2) | ||||
| Mn4-O6 | 2.2389(18) | Ba2-XPM2 | 2.7137(19) | ||||
| Si2-O4 | 1.6362(19) | Mn4-O10 | 2.2177(19) | Average | 2.915 | ||
| Si2-O5 | 1.6281(18) | Mn4-O10′ | 2.2404(17) | BVS | 1.91 | ||
| Si2-O6 | 1.6225(19) | Mn4-O12 | 2.2420(16) | ||||
| Si2-O7 | 1.6271(17) | Mn4-XOM2 | 2.1414(18) | Mn6-O1 | 2.351(2) | ||
| Average | 1.629 | Mn4-XOA2 | 2.1086(18) | Mn6-O13 | 2.6023(18) | ||
| BVS | 3.95 | Average | 2.198 | Mn6-O14 | 2.2033(16) | ||
| BVS | 1.98 | Mn6-O15 | 2.056(2) | ||||
| Si3-O8 | 1.614(2) | Mn6-O16 | 2.195(2) | ||||
| Si3-O9 | 1.6169(17) | Mn5-O10 | 2.1201(17)×2 | Mn6-O17 | 2.1943(19) | ||
| Si3-O10 | 1.6304(18) | Mn5-XOM2 | 2.3663(19)×2 | Mn6-XPM1 | 2.5870(17) | ||
| Si3-O11 | 1.6446(18) | Mn5-XOA2 | 2.1481(17)×2 | Average | 2.313 | ||
| Average | 1.627 | Average | 2.212 | BVS | 1.96 | ||
| BVS | 3.98 | BVS | 1.97 | ||||
| Mn7-O5 | 2.5729(17) | ||||||
| Si4-O11 | 1.6419(19) | Mn7-O7 | 2.2178(18) | ||||
| Si4-O12 | 1.6218(19) | Mn7-O8 | 2.3422(19) | ||||
| Si4-O13 | 1.6228(17) | Mn7-O18 | 2.058(2) | ||||
| Si4-O14 | 1.6280(18) | Mn7-O19 | 2.196(3) | ||||
| Average | 1.629 | Mn7-O20 | 2.1951(19) | ||||
| BVS | 3.95 | Mn7-XPM2 | 2.581(3) | ||||
| Average | 2.309 | ||||||
| BVS | 1.96 | ||||||
Synchrotron powder XRD patterns were collected using a large Debye-Scherrer camera equipped with MYTHEN2 detectors installed at the powder diffraction BL02B2 beamline of SPring-8, Hyogo, Japan (Kawaguchi et al., 2017). The wavelength of the incident X-ray was determined to be λ = 0.7751177 Å using CeO2 as a standard. Measurements were performed at room temperature with an exposure time of 300 s. The lattice parameters refined by least-squares fitting using 39 peaks with a large d-value were a = 5.3349(9) Å, b = 13.884(2) Å, c = 14.270(3) Å, α = 98.785(15)°, β = 93.836(16)°, γ = 90.029(16)°, and V = 1043.7(3) Å3 (Table S4). The parameters [d in Å (Iobs.) hkl] for the eight observed strongest lines for horiite in the 3° ≤ 2θ ≤ 17° range (15 ≥ d ≥ 2.6 Å) in the powder XRD pattern were 4.6911 (35) 003, 3.2217 (31) 041, 3.2074 (33) 1$\bar{2}$3, 2.9118 (51) 042 and 12$\bar{4}$, 2.8710 (24) 140, 2.8146 (100) 005, 2.7717 (31) 1$\bar{4}$2, and 2.6524 (36) 1$\bar{2}\bar{4}$ and 20$\bar{1}$.
Horiite is a member of the bafertisite group of the seidozerite supergroup as Ti = 2 apfu per (Si2O7)2 in the TS block (Sokolova and Cámara, 2017). Its structure is a combination of an I block and a TS block consisting of O and H sheets (Fig. 6). The general formula of this structure can be written as AP2BP2MO4MH2(Si2O7)2(TO3XPM)2(XOM)2(XOA)2 according to the formula notation of the seidozerite supergroup, where AP and BP are cations in the peripheral sites in the I block, MO and MH are cations consisting of the O and H sheets, T is cation with tetrahedral coordination in the I block, and XOM and XOA are apical anions for the MH and AP cations at the periphery of the TS block, respectively. XPM is also apical anions for the MH cation. Such labels are based on the structure topology, whereas using atomic symbols is clearer when describing the structures of individual minerals. Therefore, in the present study, cation sites are denoted by atomic names, whereas only the key anion sites are described using topology-based site name (Fig. 6).
As a result, this structure includes two Ba, seven Mn, two Ti, four Si, two P, and twenty-six O sites as crystallographically independent sites (Table 3). The TS block consists of a central O sheet of Mn(O,OH)6 octahedra, flanked by the H sheets consisting of two SiO4 tetrahedra that link to Si2O7 groups, together with TiO6 octahedra. The I block between TS blocks includes the polyhedra for Ba and Mn as the peripheral sites and the PO4 tetrahedra. The structure of horiite is not previously known within the bafertisite group but can be understood through appropriate comparisons.
Horiite and hejtmanite often coexist as layered aggregates (Fig. 3); however, their composition and structure are not closely related. By contrast, horiite and yoshimuraite rarely occur together, but their compositions and structures are closely related. Figure 7 shows a structural and compositional comparison among horiite, yoshimuraite, and hejtmanite. Notably, the structure of yoshimuraite used for comparison is a revised version of the structure reported by McDonald et al. (2000), in which typographical errors were corrected, and the crystallographic orientation was updated following the work of Sokolova and Cámara (2013). Within the I block, horiite includes the Ba and Mn sites, which are approximately consistent with the Ba positions in yoshimuraite, except that the Ba2 site in yoshimuraite is replaced by Mn in horiite. Along with the difference in the Ba/Mn ratio in the I block, the major differences between horiite and yoshimuraite are the coordination number of the Ti-centered polyhedron in the TS block, the position of the PO4 tetrahedron in the I block, and the b-axis length. The Ti-centered polyhedron is TiO6 in horiite and TiO5 in yoshimuraite. The PO4 tetrahedron is in a position to connect with the Ti-centered polyhedron in horiite but is separated from it in yoshimuraite. The b-axis length in horiite (∼ 14 Å), in which the SiO4 tetrahedra and TiO6 octahedra are slightly rotated along the c-axis, is approximately twice that of yoshimuraite (∼ 7 Å), which has no such rotation.
As a result, horiite, Ba2Mn2Mn4Ti2(Si2O7)2(PO4)2O2(OH)2, is a Mn-substituted form of yoshimuraite, Ba4Mn4Ti2(Si2O7)2(PO4)2O2(OH)2, in terms of composition but has a different structure—a new basic structural type in the bafertisite group. According to the nomenclature of the seidozerite supergroup, the structure of horiite should be classified as B5(BG), meaning the fifth basic structure in the bafertisite group (Table 5).
| Mineral Structure type* |
Ideal formula |
| Structure formula | |
| Unit-cell parameters (space group) | |
| Horiite B5(BG) |
Ba2Mn2Mn4|6|Ti2(Si2O7)2(PO4)2O2(OH)2 |
| AP2BP2MO4MH2(Si2O7)2(TO3XPM)2(XOM)2(XOA)2 | |
| a = 5.35090, b = 13.89170, c = 14.2777 Å, α = 98.726, β = 93.8420, γ = 90.0570° (P$\bar{1}$) [1] | |
| Bussenite B4(BG) |
Ba2Ba2(Na□)2(FeNa)2|6|Ti2(Si2O7)2[(CO3)2F2]O2(OH)2(H2O)2 |
| AP2BP2AI2MO4MH2(Si2O7)2[(CO3)2F2](XOM)2(XOA)2(XPM)2 | |
| a = 5.399, b = 7.016, c = 16.254 Å, α = 102.44, β = 93.18, γ = 90.10° (P$\bar{1}$) [2] | |
| Yoshimuraite B3(BG) |
Ba2Ba2Mn4|5|Ti2(Si2O7)2(PO4)2O2(OH)2 |
| AP2BP2MO4MH2(Si2O7)2(TO4)2(XOM)2(XOA)2 | |
| a = 5.386, b = 6.999, c = 14.748 Å, α = 95.50, β = 93.620, γ = 89.980° (P$\bar{1}$) [3]** | |
| Bafertisite B2(BG) |
Ba2Fe4|6|Ti2(Si2O7)2O2(OH)2F2 |
| AP2MO4MH2(Si2O7)2(XOM)2(XOA)2(XPM)2 | |
| a = 10.665, b = 13.743, c = 11.721 Å, α = 90.30, β = 112.27, γ = 90.00° (C$\bar{1}$) [4] | |
| Hejtmanite B2(BG) |
Ba2Mn4|6|Ti2(Si2O7)2O2(OH)2F2 |
| AP2MO4MH2(Si2O7)2(XOM)2(XOA)2(XPM)2 | |
| a = 10.716, b = 13.795, c = 11.778 Å, α = 90.07, β = 112.24, γ = 90.03° (C$\bar{1}$) [5] | |
| Jinshajiangite B1(BG) |
BaNaFe4|6|Ti2(Si2O7)2O2(OH)2F |
| APBPMO4MH2(Si2O7)2(XOM)2(XOA)2(XPM) | |
| a = 10.7059, b = 13.7992, c = 20.760 Å, α = 90.008, β = 94.972, γ = 89.984° (C$\bar{1}$) [6] | |
| Perraultite B1(BG) |
BaNaMn4|6|Ti2(Si2O7)2O2(OH)2F |
| APBPMO4MH2(Si2O7)2(XOM)2(XOA)2(XPM) | |
| a = 10.741, b = 13.841, c = 11.079 Å, α = 108.174, β = 99.186, γ = 89.99° (C$\bar{1}$) [7] | |
| Bobshannonite B1(BG) |
BaKNa2(Mn,Na)8|6|(Nb,Ti)4(Si2O7)4O4(OH)4(O,F)2 |
| AP2BP2MO8MH4(Si2O7)4(XOM)4(XOA)4(XPM)2 | |
| a = 10.839, b = 13.912, c = 20.98 Å, α = 89.99, β = 95.05, γ = 89.998° (C$\bar{1}$) [8] | |
| Cámaraite D1(BG) |
Ba3NaFe8|6|Ti4(Si2O7)4O4(OH)4F3 |
| AP3BPMO8MH4(Si2O7)4(XOM)4(XOA)4(XPM)3 | |
| a = 10.678, b = 13.744, c = 21.40 Å, α = 99.28, β = 92.38, γ = 90.00° (C$\bar{1}$) [9] |
* Notation based on the concept according to the nomenclature of the seidozerite supergroup.
** Corrected value by Sokolova and Cámara (2013).
[1] This study, [2] Zhou et al. (2002), [3] McDonald et al. (2000), [4] Cámara et al. (2016a), [5] Sokolova et al. (2016), [6] Cámara et al. (2016b), [7] Sokolova et al. (2021), [8] Sokolova et al. (2015b), [9] Cámara et al. (2009).
The bafertisite group is defined by Ti = 2 apfu per (Si2O7)2 in the TS block of the seidozerite supergroup and, with the addition of the newly discovered horiite, now consists of nine species (Table 5). Notably, surkhobite has already been discredited as being identical to perraultite (Sokolova et al., 2020). Horiite is the only species among the more than 50 in the seidozerite supergroup that contains species defining Mn-occupied sites in the I block.
In the bafertisite group, the species containing PO4 are horiite and yoshimuraite. Notably, yoshimuraite from the Noda-Tamagawa mine was originally described as having a composition with S > P (Watanabe et al., 1961). Nonetheless, McDonald et al. (2000) conducted their structural analysis using a P-rich specimen from the Taguchi mine. As a result, the ideal composition of yoshimuraite was re-written as a P-dominant formula, which differed from the original composition. Considering these circumstances, it is necessary to re-examine whether the type specimen of yoshimuraite from the Noda-Tamagawa mine is consistent with the currently defined yoshimuraite.
One of the authors (S.I.) expresses sincere gratitude to the late Dr. Hori for having suggested the possible presence of an unknown mineral associated with hejtmanite. This study uses research equipment shared in the MEXT Project for Promoting Public Utilization of Advanced Research Infrastructure (Program for supporting construction of core facilities) Grant Nos. JPMXS0440400024 and JPMXS0440400025. Synchrotron radiation X-ray powder diffraction experiments were performed at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2024A1895).
Supplementary Documents, Tables S1-S4, and CIF file are available online from https://doi.org/10.2465/jmps.260301.
