Amaterasuite, Sr₄Ti₆Si₄O₂₃(OH)Cl, a new mineral from jadeitite, a representative stone of Japan

Abstract

Amaterasuite is a new mineral found in jadeitite, a representative stone of Japan, and was thus named after Amaterasu Omikami, one of the most important goddesses in Japanese mythology, as a tribute to Japanese stone culture. The new mineral was found in the Osayama mountain area, Osa-osakabe, Niimi City, Okayama Prefecture, Japan. Amaterasuite appears as bundles consisting of needle- to plate-shaped crystals as large as 150 µm around rutile. The Mohs hardness is 6. Its tenacity is brittle, and its calculated density is 4.0 g·cm⁻³. Under plane-polarized light, the mineral is pleochroic, changing from blue to brown. The empirical formula, calculated on the basis of 23 O + 2 (OH,Cl) atoms per formula unit, is (Sr_3.32Ba_0.64)_Σ3.96(Ti_5.73Fe_0.16Nb_0.02)_Σ5.91Si_4.15O₂₃(OH)_0.95Cl_1.05; thus, its ideal formula is Sr₄Ti₆Si₄O₂₃(OH)Cl. The unit-cell parameters refined by powder X-ray diffraction using 80 peaks with large d-values are a = 5.85558(2) Å, b = 20.43960(8) Å, c = 33.28240(12) Å, and V = 3983.43(3) ų (Z = 8) in the orthorhombic Fddd space group. The structure of amaterasuite from the metajadeitite area was fully identified as amaterasuite-4O, which is characterized by its dual nature, encapsulating two types (A and B) within a unit cell. The occupancy rates of the A and B types were estimated to be ∼ 85 and ∼ 15%, respectively. The refined site occupancies at the SrA and BaB sites indicate a strong site preference for Sr, similar to the preferential site occupancies in synthetic titanosilicate compounds.

INTRODUCTION

Jadeitite is a nearly monomineralic rock composed mainly of jadeite. Because of its strength and toughness, it was used as a hammer stone ∼ 7000 years ago during the Jomon period in Japan, and this use of jadeitite is one of the oldest jadeite cultures in the world (Niigata Prefecture Archeological Research Corporation, 2006). Recent evidence suggests that jadeitite is formed only at divergent plate boundaries with cold temperature gradients, such as the Japanese islands, where aqueous fluids rising from the subducting oceanic crust condense to form jadeitite (e.g., Harlow et al., 2015). In recognition of the scientific importance and the preciousness of jadeitite, the Japan Association of Mineralogical Sciences designated ‘jadeite (jadeitite)’ as the national stone of Japan in September 2016 (Tsuchiyama, 2017). A comprehensive petrological understanding of Japanese jadeitite is summarized in the works of Tsujimori (2017) and Tsujimori and Harlow (2017). Japanese jadeitite corresponds to the oldest known jadeitite, and the latest related study reported that the Osayama jadeitite formed 523.6 ± 3.5 Ma (Peverelli et al., 2025).

In Japan, jadeitite has been found in the Itoigawa, Wakasa, and Osayama areas and is characterized by the occurrence of Sr-rich accessory minerals. Itoigawaite [SrAl₂Si₂O₇(OH)₂·H₂O], rengeite [Sr₄Ti₄ZrO₈(Si₂O₇)₂], and matsubaraite [Sr₄Ti₅O₈(Si₂O₇)₂] were found as new minerals from the Itoigawa jadeitite (Miyajima et al., 1999, 2001, 2002). Sr-bearing titanosilicates ohmilite [Sr₃(Ti,Fe³⁺)(Si₂O₆)₂(O,OH)·2H₂O] and strontio-orthojoaquinite [NaSr₄Fe³⁺Ti₂Si₈O₂₄(OH)₄] have also been discovered as new minerals in albitite associated with the Itoigawa jadeitite (Komatsu et al., 1973; Chihara et al., 1974; Wise, 1982). In the prehnite rock in the Itoigawa area, niigataite [CaSrAl₃(Si₂O₇)(SiO₄)O(OH)] was found as a new member of the epidote group (Miyajima et al., 2003). Among them, itoigawaite was also found in the Wakasa jadeitite (Shimobayashi and Yamada, 2003). Recently, Nishio-Hamane and Tanabe (2021) reported the occurrence of matsubaraite and rengeite in the Osayama jadeitite. Their report also indicated the occurrence of an undetermined Sr-rich mineral, which was subsequently approved as a new mineral, amaterasuite, with composition Sr₄Ti₆Si₄O₂₃(OH)Cl.

The relationship between jadeitite and the Japanese people dates to ancient times. Today, jadeitite is recognized as a representative stone of Japan, and amaterasuite is a new mineral discovered among these symbolic stones. Therefore, as a tribute to Japanese stone culture, the new mineral, amaterasuite, was named after Amaterasu Omikami (also known as Amaterasu for short), the goddess of the sun in Japanese mythology. Her name appears in ‘Kojiki’ and ‘Nihon Shoki’, the oldest chronicles in Japanese history, compiled around 710-720 AD. The commonality of duality was also one of the reasons for the naming: Amaterasu has a duality of spirits, Ara-Mitama (wild spirit) and Nigi-Mitama (gentle spirit), and amaterasuite has a dual nature in its crystal structure (described below). The mineral and its name of amaterasuite (IMA No. 2024-056) 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 M-52596).

OCCURRENCE

The type locality (35°05′38′′N 133°33′01′′E) is located at the northeastern part of the Osayama mountain area, Osa-osakabe, Niimi City, Okayama Prefecture, Japan, where jadeitite and its related rocks are distributed in association with serpentinite mélange (e.g., Tsujimori, 1998). There, one of the authors, M.T., found a ∼ 1 m jadeitite block buried at the boundary between serpentinite and rodingite (Supplementary Fig. S1; Figs. S1-S3 are available online from https://doi.org/10.2465/jmps.250420). Most of the block was composed of jadeite, while the area in contact with the rodingite contained a substantial amount of prehnite, which we refer to as the metajadeitite area. It is noted that ‘metajadeitite’ is not a common petrological term, but a classification term in this paper. Jadeitite also contained veins of edenite; however, in the metajadeitite area, edenite disappeared and was replaced by chlorite (Fig. S1). By contrast, rutile contained in jadeitite remained even in the metajadeitite. Amaterasuite occurs in both jadeitite and metajadeitite, although their occurrence and appearance differ.

In jadeitite, rutile is often surrounded by titanite, forming rutile (core) + titanite (rim) aggregates as large as ∼ 1 mm (Fig. 1a). Amaterasuite occurs by filling fine cracks a few micrometers wide in rutile, and the Sr-Ba minerals such as matsubaraite, tausonite, and henrymeyerite occur in common formations similar to amaterasuite (Fig. 1b). These minerals can only be observed by electron microprobe and distinguished by analysis because of their small size and lack of color. In rutile, amaterasuite is distributed discontinuously along the cracks; individual grains cannot be recognized. The same features are observed in other Sr-Ba minerals.

Figure 1. The representative occurrence of amaterasuite from jadeitite [(a) and (b)] and the metajadeitite area [(c) and (d)]. Amaterasuite often occurs by filling cracks in rutile in association with Sr-Ba minerals in jadeitite [(a) and (b)], whereas it occurs in titanite surrounding rutile in the metajadeitite area [(c) and (d)].

In the metajadeitite area, rutile (core) + titanite (rim) aggregate remains. However, most of the cracks in rutile are replaced by titanite; thus, the occurrence of Sr-Ba minerals becomes scarce. Amaterasuite is also rarely found in the cracks in rutile; it is instead found in the titanite rim (Figs. 1c and 1d). In this occurrence, amaterasuite is larger than that in jadeitite, reaching more than 100 µm, and can be observed with an optical microscope. For the other Sr-Ba minerals, the difference in the occurrence of tausonite is remarkable. It occurs mainly at the boundary between rutile and titanite and on the outer edge of titanite; in addition, the grains have grown significantly. As a result, in the metajadeitite area, aggregates of rutile, titanite + amaterasuite, and tausonite are occasionally found because their appearance differs from that of simple rutile (Fig. S2).

These occurrences suggest that there may be multiple reaction pathways to the formation and growth of amaterasuite, whereas all occurrences appear to start with rutile, a common mineral often associated with jadeitite. Because the occurrences are very small and few, amaterasuite may be a common but often overlooked mineral in rutile-bearing jadeitite.

PHYSICAL AND OPTICAL PROPERTIES

Amaterasuite, which can be observed with an optical microscope, is only found in the metajadeitite area, and its properties are described here. Amaterasuite often appears as bundles consisting of needle- to plate-shaped crystals as large as 150 µm. The mineral has a transparent deep-blue to green color with vitreous luster, whereas its streak is white. Amaterasuite is nonfluorescent, brittle, and uneven in fracture. Cleavage or parting could not be determined. Its Mohs hardness, as measured by rubbing a reference mineral powder against a sample fixed onto a glass slide, is 6. Its density is 4.0 g·cm⁻³, as calculated from the empirical formula and single-crystal X-ray diffraction (XRD) data.

The refractive indices (α, β, and γ) of amaterasuite are all in the range between 1.81 (methylene iodide + sulfur + tetraiodoethylene) and 2.30 (sulfur-selenium melt). Although a specific value could not be determined because we did not have a medium with an adjustable refractive index, the mean refractive index obtained from the Gladstone-Dale relationship (Mandarino, 1981) using the empirical formula is 2.03, consistent with the observation (1.81 < n < 2.30). Amaterasuite is pleochroic, changing from blue to brown under plane-polarized light (Fig. S3). The orientation of the crystals could not be determined from the observations.

RAMAN SPECTROSCOPY

Raman spectroscopic analysis of amaterasuite from the metajadeitite area was carried out using a Renishaw inVia Reflex spectrometer at the Institute for Solid State Physics, University of Tokyo (ISSP). The spectrum was obtained from 100 to 4000 cm⁻¹ using a 532 nm diode laser (Fig. 2). The O-H stretching vibration at 3503 cm⁻¹ is observed in the Raman spectra of amaterasuite, whereas the O-H bending mode (∼ 1640 cm⁻¹) is not observed. Therefore, only the OH group is considered to be present in amaterasuite structure; no water molecules are present. Although several Raman bands are observed in the lattice-vibration region, their specific assignments remain unavailable.

Figure 2. Raman spectrum of amaterasuite in the metajadeitite area.

CHEMICAL COMPOSITION

Chemical analyses for the type specimen were conducted using a JEOL JXA-8105 (WDS mode, 15 kV, 10 nA, 3 µm beam diameter) at the Department of Geology and Mineralogy, Kyoto University. For other specimen, a JEOL IT-100 (EDS mode, 15 kV, 0.8 nA, 1 µm beam diameter) at ISSP was used. The ZAF method was used for data correction in both the WDS and EDS analyses. The standards used in these analyses were silicon for Si, tausonite for Sr and Ti, hematite for Fe, LaNbO₄ for Nb, BaTiSi₃O₉ for Ba, and Ba₅(ReO₅)₃Cl for Cl. Although insufficient 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 by stoichiometry. The analytical data are shown in Table 1. The slightly low total wt% in WDS analysis is probably due to electron damage because the EDS measurements performed at low current did not result in a deficiency of wt%. However, the WDS values were adapted as new mineral data in the type specimen because it could avoid the Sr-Si and Ba-Ti peak overlaps. The empirical formula of type specimen amaterasuite from the metajadeitite area, as calculated on the basis of 23 O + 2 (OH,Cl), is (Sr_3.32Ba_0.64)_Σ3.96(Ti_5.73Fe_0.16Nb_0.02)_Σ5.91Si_4.15O₂₃(OH)_0.95Cl_1.05. The composition of amaterasuite in rutile in jadeitite is (Sr_3.39Ba_0.65)_Σ4.04(Ti_6.00Fe_0.11Nb_0.05)_Σ6.16Si_3.83O₂₃(OH)_1.04Cl_0.96. The ideal formula is Sr₄Ti₆Si₄O₂₃(OH)Cl, which requires SrO 35.41, TiO₂ 40.95, SiO₂ 20.53, H₂O 0.77, Cl 3.03, -O = Cl 0.68, and Total 100 wt%.

Table 1. Chemical compositions of amaterasuite

	In metajadeitite			In jadeitite
	(type specimen)
	WDS analysis			EDS analysis
	wt% (n = 22)			wt% (n = 5)
	Avg.	Range		Avg.	Range
SiO2	20.21	19.76-20.55	SiO2	19.18	18.54-19.42
TiO2	37.10	35.94-37.96	TiO2	39.94	38.82-40.99
Fe2O3	1.01	0.65-1.53	Fe2O3	0.75	0.59-0.75
Nb2O5	0.19	0.04-0.37	Nb2O5	0.54	0.07-0.97
SrO	27.92	24.96-29.38	SrO	29.27	28.64-29.90
BaO	8.01	6.63-9.99	BaO	8.32	7.37-9.05
Cl	3.01	2.78-3.29	Cl	2.83	2.60-2.93
H2O*	0.70		H2O*	0.78
-O = Cl	0.68		-O = Cl	0.64
Total	97.47		Total	100.97
	apfu			apfu
Sr	3.32		Sr	3.39
Ba	0.64		Ba	0.65
Σ	3.96		Σ	4.04
Ti	5.73		Ti	6.00
Fe	0.16		Fe	0.11
Nb	0.02		Nb	0.05
Σ	5.91		Σ	6.16
Si	4.15		Si	3.83
O =	23		O =	23
OH**	0.95		OH**	1.04
Cl	1.05		Cl	0.96
Σ =	2		Σ =	2

^* Calculated value from stoichiometry.

^** OH is estimated as 2 − Cl.

CRYSTAL STRUCTURE

Amaterasuite [Sr₄Ti₆Si₄O₂₃(OH)Cl] and a titanosilicate compound, (Ba,Sr)₄Ti₆Si₄O₂₄·H₂O, reported by Cadoni et al. (2008) have similar stoichiometry in terms of 4Sr(Ba) + 6Ti + 4Si and 25(O + Cl); they are therefore structurally related. The structure of the titanosilicate compound was solved as a disordered structure of the orthorhombic Cmmm space group (a = 5.906 Å, b = 20.618 Å, and c = 16.719 Å) and was then deciphered to an ordered structure of the monoclinic P2/c space group (a = 5.906 Å, b = 16.719 Å, c = 10.724 Å, and β = 105.99°) on the basis of the order-disorder theory developed by Dornberger-Schiff (1964) and Ferraris et al. (2004). However, another polytype with different stacking sequences has been proposed: the 4O polytype with a disordered structure of the orthorhombic Fddd space group with a c-axis length approximately twice that of the Cmmm space-group model (c ∼ 33.5 Å). Cadoni et al. (2008) mentioned this 4O polytype, although they did not refine the structure, because it was not present in their titanosilicate compounds.

Electron diffraction

Polytypes are occasionally intermixed. Thus, we investigated the crystal quality by electron diffraction using a transmission electron microscope (JEOL JEM-2100, operating at 200 kV) at ISSP. Samples were prepared using amaterasuite from the metajadeitite area by Ar⁺-ion milling using an ion-slicer (JEOL EM-09100IS).

All of the electron diffraction patterns for amaterasuite could be indexed to the orthorhombic symmetry. Figure 3 shows the observed and simulated electron diffraction patterns from [110] and [100], which are key to determining the polytype. The observed electron diffraction patterns of amaterasuite are clearly consistent with the Fddd space-group model. In addition, because no spots or streaks indicative of other polytypes were observed, amaterasuite from the metajadeitite area can be regarded as a single phase of the 4O polytype.

Figure 3. Observed and simulated selected-area electron diffraction patterns from [110] and [100] of amaterasuite from the metajadeitite area. The simulations were performed using the ReciPro program with dynamical theory (Seto and Ohtsuka, 2022). The observed electron diffraction patterns of amaterasuite are understood only under the Fddd model. In space group Fddd, the 002 reflection violates the extinction rules, but can occur due to multiple reflections (e.g., when the origin is moved to a reflection in the left or right column).

X-ray diffraction

The XRD data for a single crystal of amaterasuite 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 from the metajadeitite area 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 of the intensity data. The diffraction data and empirical absorption correction were processed using CrysAlis^Pro (Matsumoto et al., 2021). The SHELXL-2019/3 software (Sheldrick, 2015) was used for refinement of the crystal structure with neutral atom-scattering factors. The reflection statistics and systematic absences were set to the Fddd space group, as confirmed by the electron diffractions. The structure model was then solved using the direct method.

During the process of crystal structure refinement, the hydrogen position (H6A) of the hydroxyl groups around O6 was derived from difference-Fourier synthesis. However, the O6-H6A configuration means that both the donor and the acceptor are O6. Thus, the occupancy of hydrogen at H6A was fixed as 0.25 from a stoichiometric perspective. The displacement parameter of the H atom was fixed as the value of U_iso = 0.05 Ų, with a restraint of O-H = 0.980(1) Å applied (Franks, 1973). The displacement parameters of the other atoms were analyzed anisotropically, whereas that of the O2B site resulted in a large value, which was reported as alert level A by checkCIF. This issue can be avoided by analyzing U_iso or by fixing the value obtained at the O2A site. However, because the parameters converged to positive values, we used the results of anisotropic refinement. The refinement converged to R₁ = 5.03% for 2393 unique reflections with I > 2σ₁.

Details related to 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.250420). The final atom coordinates and equivalent isotropic atomic displacement parameters are summarized in Table 3. Selected interatomic distances are shown in Table 4, and bond valences are reported in Table 5. The refined unit-cell parameters were a = 5.8603(3), b = 20.4616(7), c = 33.2810(12) Å, and V = 3990.8(2) ų (Z = 8) in the orthorhombic Fddd (#70-2) space group.

Table 2. Experimental details of the single-crystal XRD analysis of amaterasuite

Crystal size (mm)		0.02 × 0.04 × 0.06
Space group		Fddd
Unit-cell dimensions	a (Å)	5.8603(2)
	b (Å)	20.4616(7)
	c (Å)	33.281(1)
	V (Å3)	3990.75(2)
Dcalc (g/cm3)		4.02
Radiation		MoKα (λ = 0.71073 Å)
Monochromator		VariMax optics
Diffractometer		Rigaku XtaLAB Synergy-R/DW with HyPix-6000HE
Scan type		ω scan
Absorption correction		CrysAlisPro (Matsumoto et al., 2021)
Absorption coefficient μ (mm−1)		12.83
θmin-θmax(°)		2.3-36.3
Collected reflections		12346
Unique reflctions		2393
Rint (%)		6.82
Index ranges	h	−9 → 9
	k	−33 → 34
	l	−55 → 55
Refinement on F2 using		SHELXL-2019/3 (Sheldrick, 2015)
R1 (%)		5.03
wR2 (%)		11.75
No. of parameters		136
Weighting scheme*		w = 1/[σ2(Fo2) + (0.0454P)2 + 54.10P]
Δρmax (e Å−3)		1.09 at 0.90 Å from O2A
Δρmin (e Å−3)		−1.32 at 0.89 Å from SrA

^* The function of the weighting scheme is w = 1/[σ²(F_o²) + (a·P)² + b·P], where P = [Max(F_o²) + 2F_c²]/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.

Table 3. Refined atomic positions with occupancy and anisotropic displacement parameters (Ų) of amaterasuite

	W	x	y	z	Ueq	Occupancy
SrA	32h	0.61652(7)	0.52278(2)	0.56069(2)	0.01249(12)	Sr0.746(6)Ba0.104
BaB	32h	0.1311(5)	0.52238(13)	0.56073(9)	0.0277(8)	Ba0.078(5)Sr0.072
Ti1A	32h	0.1309(4)	0.38506(6)	0.52604(5)	0.0140(3)	Ti0.85
Ti1B	32h	0.115(3)	0.3648(4)	0.5255(4)	0.0220(19)	Ti0.15
Ti2	16g	7/8	3/8	0.62409(3)	0.00906(19)	Ti1.0
Si1A	16f	1/8	0.51347(8)	5/8	0.0076(3)	Si0.85
Si2A	16g	1/8	5/8	0.55867(5)	0.0075(3)	Si0.85
Si1B	16f	5/8	0.5137(6)	5/8	0.018(2)	Si0.15
Si2B	16g	5/8	5/8	0.5582(4)	0.020(2)	Si0.15
O1	32h	0.1284(5)	0.37254(14)	0.58594(9)	0.0125(5)	O1.0
O2A	32h	0.1373(8)	0.55874(18)	0.58503(13)	0.0191(8)	O0.85
O2B	32h	0.611(5)	0.5611(13)	0.5862(8)	0.031(6)	O0.15
O3	32h	0.3644(5)	0.62733(16)	0.53397(9)	0.0148(5)	O1.0
O4	32h	0.6216(6)	0.56155(15)	0.47632(9)	0.0128(5)	O1.0
O5	32h	0.8860(5)	0.47248(13)	0.62393(10)	0.0127(5)	O1.0
O6	32h	0.8726(6)	0.43962(16)	0.52656(10)	0.0149(6)	O1.0
ClA	8b	5/8	5/8	5/8	0.0163(4)	Cl0.85
ClB	8a	1/8	5/8	5/8	0.018(2)	Cl0.15
H6A	32h	0.961(10)	0.469(2)	0.5095(16)	0.05 Uiso	H0.25
	U11	U22	U33	U12	U13	U23
SrA	0.01148(19)	0.01007(18)	0.0159(2)	−0.00379(13)	−0.0005(2)	−0.00033(18)
BaB	0.0295(14)	0.0240(13)	0.0294(14)	−0.0037(9)	0.0032(15)	−0.0010(13)
Ti1A	0.0205(6)	0.0136(6)	0.0078(4)	−0.0006(5)	0.0000(5)	−0.0074(6)
Ti1B	0.033(4)	0.021(4)	0.012(3)	−0.005(4)	−0.004(3)	−0.014(5)
Ti2	0.0097(4)	0.0075(3)	0.0100(4)	0	0	−0.0008(3)
Si1A	0.0062(7)	0.0075(7)	0.0092(7)	0	0.0009(8)	0
Si2A	0.0054(7)	0.0096(7)	0.0074(7)	0	0	0.0001(7)
Si1B	0.014(5)	0.024(6)	0.017(5)	0	0.007(6)	0
Si2B	0.030(6)	0.007(4)	0.023(6)	0	0	0.004(5)
O1	0.0101(12)	0.0171(12)	0.0103(11)	0.0006(10)	−0.0002(11)	0.0002(17)
O2A	0.0217(19)	0.0126(15)	0.0231(19)	0.0081(14)	0.000(2)	−0.0018(17)
O2B	0.035(15)	0.029(13)	0.029(13)	0.002(10)	0.010(14)	−0.029(13)
O3	0.0107(13)	0.0243(15)	0.0094(11)	0.0003(11)	−0.0004(11)	0.0019(17)
O4	0.0086(12)	0.0138(12)	0.0159(13)	0.0008(10)	−0.0013(15)	−0.0008(13)
O5	0.0115(12)	0.0108(11)	0.0158(12)	−0.0011(10)	0.0007(15)	0.0002(9)
O6	0.0096(12)	0.0171(13)	0.0180(15)	0.0005(11)	−0.0002(15)	0.0023(13)
ClA	0.0201(11)	0.0135(9)	0.0151(10)	0	0	0
ClB	0.015(6)	0.018(6)	0.020(6)	0	0	0

Table 4. Selected bond distances in amaterasuite

Type A			Type B
SrA-	O1	3.090(3)	BaB-	O1	3.179(4)
	O2A	3.014(5)		O2B	3.04(3)
	O3	2.748(3)		O3	2.660(4)
	O3	2.731(3)		O3	2.697(4)
	O4	2.538(3)		O4	2.564(4)
	O4	2.918(3)		O5	2.763(4)
	O5	2.826(3)		O5	2.744(4)
	O5	2.826(3)		O6	2.540(4)
	O6	2.537(3)		O6	3.007(5)
	ClA	2.9930(6)		ClB	2.998(3)
	X<SrA-O>	2.822		X<BaB-O>	2.819
Ti1A-	O1	2.010(3)	T1B-	O1	2.019(12)
	O4	1.818(4)		O4	1.857(15)
	O3	2.006(3)		O3	1.996(12)
	O4	2.064(4)		O4	2.158(11)
	O6	1.881(4)		O6	1.783(12)
	O6	2.131(4)		O6	2.090(14)
	VI<Ti1A-O>	1.985		VI<Ti1B-O>	1.984
T2-	O1 (×2)	1.954(3)	T2-	O1 (×2)	1.954(3)
	O1 (×2)	1.965(3)		O1 (×2)	1.965(3)
	O5 (×2)	1.996(3)		O5 (×2)	1.996(3)
	VI<Ti2-O>	1.972		VI<Ti2-O>	1.972
Si1A-	O2A (×2)	1.623(4)	Si1B-	O2B (×2)	1.62(3)
	O5 (×2)	1.633(3)		O5 (×2)	1.748(7)
	IV<Si1A-O>	1.628		IV<Si1B-O>	1.68
Si2A-	O2A (×2)	1.617(4)	Si2B-	O2B (×2)	1.61(3)
	O3 (×2)	1.627(3)		O3 (×2)	1.728(7)
	IV<Si2A-O>	1.622		IV<Si2B-O>	1.67

Table 5. Bond-valence analysis of amaterasuite weighted on the refined site occupancies^*

	SrA	BaB	Ti1A	Ti1B	Ti2	Si1A	Si1B	Si2A	Si2B	Sum
O1	0.08	0.01	0.49	0.08	0.67×2↓					1.98
					0.65×2↓
O2A	0.10	0.02				0.85×2↓		0.87×2↓		2.14
O2B							0.15×2↓		0.16×2↓
O3	0.17	0.04	0.49	0.09				0.84×2↓	0.11×2↓	1.96
	0.18	0.04
O4	0.27	0.05	0.85	0.13						1.90
	0.12		0.42	0.06
O5	0.14	0.03			0.60×2↓	0.83×2↓	0.11×2↓			1.88
	0.14	0.03
O6	0.27	0.05	0.71	0.17						1.63
		0.02	0.34	0.07
ClA	0.25×4→									1.20
ClB		0.05×4→
Sum	2.07		3.90		3.84	3.88		3.96

^* The bond valence sums were calculated using the parameters of Brown and Altermatt (1985) and Gagné and Hawthorne (2015) for cation-Cl bonds and cation-O bonds, respectively.

Synchrotron powder XRD patterns were collected using a large Debye-Scherrer camera equipped with MYTHEN2 detectors and installed at the powder diffraction BL02B2 beamline of SPring-8, Hyogo, Japan (Kawaguchi et al., 2017). Rock samples of the metajadeitite area were roughly crushed, and the target minerals were then selected. Powder samples were packed into a borosilicate glass capillary with an outer diameter of 0.3 mm and a glass wall thickness of 0.01 mm. The wavelength of the incident X-rays was determined to be λ = 0.93186 Å using a CeO₂ standard. Measurements were performed at room temperature (296 K) with an exposure time of 600 s.

The XRD pattern showed the presence of titanite and tausonite in addition to amaterasuite because of its occurrence; thus, we applied the Le Bail analysis for peak identification using the JANA2006 software (Petříček et al., 2014). The pattern fitting under the three-phase model converged to R_wp = 2.44% (Fig. 4), and 370 peaks of amaterasuite were identified in the 5° ≤ 2θ ≤ 50° range. The lattice parameters refined by least-squares fitting using 80 peaks with a large d-value were a = 5.85558(2) Å, b = 20.43960(8) Å, c = 33.28240(12) Å, and V = 3983.43(3) ų (Supplementary Table S1; Table S1 is available online from https://doi.org/10.2465/jmps.250420). The parameters [d in Å (I_obs.) hkl] for the seven observed strongest lines of amaterasuite in the 5° ≤ 2θ ≤ 50° range (11 ≥ d ≥ 1.1 Å) of the powder XRD pattern were 3.3374 (83) 062, 3.2454 (78) 137, 3.2262 (87) 048, 3.1647 (100) 0 2 10, 2.8835 (74) 202, 2.2204 (87) 260, and 1.3051 (76) 2 10 16.

Figure 4. Result of full pattern fitting of the XRD pattern (λ = 0.93186 Å) of amaterasuite-bearing aggregate in the metajadeitite area using the Le Bail method.

Discussion

Figure 5 shows the whole crystal structure of amaterasuite. The framework of the structure is formed by octahedral ribbons and tetrahedral rings, and Sr(Ba) and Cl sites are located at cavities in the framework. The TiO₆ octahedra share a corner in the c-axis direction, three of them make up one unit, and a continuous ribbon is formed in the a-axis direction by sharing edges. One ring composed of four SiO₄ tetrahedra is located at the center of the four ribbons, and the ribbons and the ring share a corner. The Sr(Ba)-centered polyhedron is located between octahedral ribbons and tetrahedral rings. This polyhedron consists of nine oxygen atoms and one chlorine, connected by shared faces in the b- and c-axis directions and shared corners in the a-axis direction, with four in one unit (Fig. 6).

Figure 5. Whole crystal structure model of amaterasuite. The framework of the structure is formed by octahedral ribbons and tetrahedral rings, and Sr(Ba) and Cl sites are located at cavities in the framework. However, the crystal structure exhibits a dual nature, encapsulating two types within a unit cell. Hence, tetrahedral ring and Sr(Ba) and Cl sites are characterized by the absence of one when the other is present.

Figure 6. Pickup diagram of the crystal structure. The crystal structure of amaterasuite is constructed by synthesizing A- and B-type structures.

However, the crystal structure exhibits a dual nature, encapsulating two types within a unit cell. Hence, the tetrahedral ring, Sr(Ba) sites, and Cl sites are characterized by the absence of one when the other is present. Figure 6 shows the details of the dual nature of the structure, where they are labeled as types A and B. The positional relationship between the types is a disorder at the Ti1 site and a 1/2 shift in the a-axis direction for the other specific sites, marked as A or B. Because the sites for Ti and Si have less substitution relationship with other atoms, the occupancy rates of the A and B types were estimated using these sites. Conclusively, A and B were refined to be 85.1 ± 2.9 and 14.9 ± 2.9%; we fixed the occupancy of the A and B types at 85 and 15%, respectively. Then, the refined site occupancies at the SrA and BaB sites were found to be Sr_0.746(6)Ba_0.104 and Ba_0.078(5)Sr_0.072, respectively, indicating a strong Sr preference for the SrA site. Although the cause of this phenomenon is still unclear, a strong site preference for Sr has also been observed in the synthetic titanosilicate compound by Cadoni et al. (2008).

In this way, amaterasuite from the metajadeitite area was fully identified as the 4O polytype structure. Thus, the full notation of amaterasuite from metajadeitite is ‘amaterasuite-4O’ according to the polytype notation of Nickel (1993). The titanosilicate compounds in which other polytypes have been observed have compositions that slightly differ from that of amaterasuite, and the relationship between the former and the latter is Ba + O + H₂O and Sr + OH + Cl, respectively. The difference in the cation size and the charge balance at each site may have stabilized the 4O structure in amaterasuite from the metajadeitite area. Differences in origin may also affect the stability of the structure. To further verify these possibilities, it is important to systematically understand solid solutions, occurrence, and structure; however, the crystal structure of amaterasuite in rutile in jadeitite could not be determined because of its small size. This issue will be the subject of future study.

RELATIONSHIP TO OTHER MINERALS

Table 6 shows the Sr-bearing titanosilicate minerals found in jadeitite and its related rocks from Japan. Amaterasuite, matsubaraite, rengeite, ohmilite, and strontio-orthojoaquinite are listed. Among them, matsubaraite is most closely related to amaterasuite in terms of occurrence, composition, and structure. Compositionally, they share the same type of cation. They are also partially structurally related, particularly in the titanates, where both have triplet TiO₆ octahedra. In amaterasuite, the TiO₆ octahedra form unidirectionally bonded ribbons, whereas they form planarly bonded sheets in matsubaraite. Indeed, amaterasuite and matsubaraite have been observed to coexist in jadeitite. This sheet is also common to rengeite, with only isolated TiO₆ octahedra in matsubaraite being replaced by ZrO₆ octahedra in rengeite.

Table 6. Sr-bearing titanosilicate minerals found in jadeitite and its related rocks from Japan

Mineral name	Composition	Titanate feature			Ref.
		Unit	Connection	Host rock
Amaterasuite	Sr4Ti6Si4O23(OH)Cl	Triplet	Ribbon	Jadeitite*	1
Matsubaraite	Sr4Ti5O8(Si2O7)2	Triplet, single	Sheet, Isolation	Jadeitite	2
Rengeite	Sr4Ti4ZrO8(Si2O7)2	Triplet	Sheet	Jadeitite	3
Ohmilite	Sr3(Ti,Fe3+)(Si2O6)2(O,OH)·2H2O	Single	Chain	Albitite	4
Strontio-orthojoaquinite	NaSr4Fe3+Ti2Si8O24(OH)4	Pair	Dimer	Albitite	5

^* including the metajadeitite area

1, This study; 2, Miyajima et al. (2002); 3, Miyajima et al. (2001); 4, Mizota et al. (1983); 5, Kato and Mizota (1990).

CONCLUSION

Amaterasuite is a new mineral with an ideal formula of Sr₄Ti₆Si₄O₂₃(OH)Cl. It is associated with jadeitite from Osayama. It was named after Amaterasu Omikami, the most important goddess in Japanese mythology, because it occurred from jadeitite, the symbol of Japanese stone culture. Rutile is closely involved in the formation of amaterasuite. Amaterasuite from the metajadeitite area was fully identified as amaterasuite-4O, which is characterized by a dual nature within a single unit cell. The correspondence of their structure to amaterasuite in other occurrences remains a subject for future study. Among the Sr-bearing titanosilicate minerals occurring in jadeitite and related rocks, amaterasuite is closely related to matsubaraite in terms of occurrence, composition, and partial structure.

ACKNOWLEDGMENTS

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). This study used research equipment shared in the MEXT Project for Promoting Public Utilization of Advanced Research Infrastructure (Program for supporting construction of core facilities) Grant No. JPMXS0440400024 and was also supported by Core Clusters for Research Initiative of Yamaguchi University. One of the authors (M.N.) gratefully acknowledges the financial support of a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science, No. 23K03551.

SUPPLEMENTARY MATERIALS

Supplementary Figures S1-S3, Table S1, and CIF file are available online from https://doi.org/10.2465/jmps.250420.

REFERENCES

•  Brown,  I.D. and  Altermatt,  D. (1985) Bond-valence parameters obtained from a systematic analysis of the inorganic crystal structure database. Acta Crystallographica, B41, 244-247.
•  Cadoni,  M.,  Bloise,  A.,  Ferraris,  G. and  Merlino,  S. (2008) Order-disorder character and twinning in the structure of a new synthetic titanosilicate: (Ba,Sr)₄Ti₆Si₄O₂₄·H₂O. Acta Crystallographica, B64, 669-675.
•  Chihara,  K.,  Komatsu,  M. and  Mizota,  M. (1974) A joaquinite-like mineral from Ohmi, Niigata Prefecture, Central Japan. Mineralogical Journal, 7, 395-399.
•  Dornberger-Schiff,  K. (1964) Grundzüge einer Theorie von OD-Strukturen aus Schichten. Abhandlungen der Deutschen Akademie der Wissenschaften, Klasse für Chemie, Geologie und Biologie, 3, 107 (in German).
• Ferraris, G., Makovicky, E. and Merlino, S. (2004) Crystallography of modular materials. Vol. 15, pp. 372, Oxford University Press, USA.
• Franks, F. (1973) Water: A comprehensive treatise. Vol. 2, pp. 684, Plenum, New York.
•  Gagné,  O.C. and  Hawthorne,  F.C. (2015) Comprehensive derivation of bond-valence parameters for ion pairs involving oxygen. Acta Crystallographica, B71, 562-578.
•  Harlow,  G.E.,  Tsujimori,  T. and  Sorensen,  S.S. (2015) Jadeitites and plate tectonics. Annual Reviews of Earth and Planetary Sciences, 43, 105-138.
•  Kato,  T. and  Mizota,  T. (1990) The crystal structure of strontio-orthojoaquinite. Journal of the Faculty of Liberal Arts. Yamaguchi University, 24, 23-32.
•  Kawaguchi,  S.,  Takemoto,  M.,  Osaka,  K.,  Nishibori,  E., et al (2017) High-throughput powder diffraction measurement system consisting of multiple MYTHEN detectors at beamline BL02B2 of SPring-8. Review of Scientific Instruments, 88, 085111.
•  Komatsu,  M.,  Chihara,  K. and  Mizota,  T. (1973) A new strontium-titanium hydrous silicate mineral from Ohmi, Niigata Prefecture, Central Japan. Mineralogical Journal, 7, 298-301.
•  Mandarino,  J.A. (1981) The Gladstone-Dale relationship: Part IV. The compatibility concept and its application. The Canadian Mineralogist, 19, 441-450.
•  Matsumoto,  T.,  Yamano,  A.,  Sato,  T.,  Ferrara,  J.D., et al (2021) “What is this?” a structure analysis tool for rapid and automated solution of small molecule structures. Journal of Chemical Crystallography, 51, 438-450.
•  Miyajima,  H.,  Matsubara,  S.,  Miyawaki,  R. and  Ito,  K. (1999) Itoigawaite, a new mineral, the Sr analogue of lawsonite, in jadeitite from the Itoigawa-Ohmi district, central Japan. Mineralogical Magazine, 63, 909-916.
•  Miyajima,  H.,  Matsubara,  S.,  Miyawaki,  R.,  Yokoyama,  K. and  Hirokawa,  K. (2001) Rengeite, Sr₄ZrTi₄Si₄O₂₂, a new mineral, the Sr-Zr analogue of perrierite from the Itoigawa-Ohmi district, Niigata Prefecture, central Japan. Mineralogical Magazine, 65, 111-120.
•  Miyajima,  H.,  Miyawaki,  R. and  Ito,  K. (2002) Matsubaraite, Sr₄Ti₅(Si₂O₇)₂O₈, a new mineral, the Sr-Ti analogue of perrierite in jadeitite from the Itoigawa-Ohmi district, Niigata Prefecture, Japan. European Journal of Mineralogy, 14, 1119-1128.
•  Miyajima,  H.,  Matsubara,  S.,  Miyawaki,  R. and  Hirokawa,  K. (2003) Niigataite, CaSrAl₃(Si₂O₇)(SiO₄)O(OH): Sr-analogue of clinozoisite, a new member of the epidote group from the Itoigawa-Ohmi district, Niigata Prefecture, central Japan. Journal of Mineralogical and Petrological Sciences, 98, 118-129.
•  Mizota,  T.,  Komatsu,  M. and  Chihara,  K. (1983) A refinement of the crystal structure of ohmilite, Sr₃(Ti,Fe³⁺)(O,OH)(Si₂O₆)₂·2-3H₂O. American Mineralogist, 68, 811-817.
•  Nickel,  E.H. (1993) Standardization of polytype suffixes. The Canadian Mineralogist, 31, 767-768.
• Niigata Prefecture Archeological Research Corporation (2006) The Ogakuchi site. pp. 85, Niigata Prefecture Archeological Research Report, 173 (in Japanese).
• Nishio-Hamane, D. and Tanabe, T. (2021) Matsubaraite, rengeite, törnebohmite-(Ce) and rare minerals in Osayama jadeitite. 2021 Annual Meeting of Japan Association of Mineralogical Sciences, R1P-09 (in Japanese).
•  Petříček,  V.,  Dušek,  M. and  Palatinus,  L. (2014) Crystallographic Computing System JANA2006: General features. Zeitschrift für Kristallographie - Crystalline Materials, 229, 345-352.
•  Peverelli,  V.,  Olivieri,  O.S.,  Tsujimori,  T.,  Giovannelli,  D., et al (2025) Cold-subduction biogeodynamics boosts deep energy delivery to the forearc. Geochimica et Cosmochimica Acta, 388, 195-207.
•  Seto,  Y. and  Ohtsuka,  M. (2022) ReciPro: free and open-source multipurpose crystallographic software integrating a crystal model database and viewer, diffraction and microscopy simulators, and diffraction data analysis tools. Journal of Applied Crystallography, 55, 397-410.
•  Sheldrick,  G.M. (2015) Crystal structure refinement with SHELX. Acta Crystallographica, C71, 3-8.
• Shimobayashi, N. and Yamada, S. (2003) Coexistence of itoigawaite and pumpellyite in jadeitite from Wakasa district, Tottori Prefecture, Japan. Abstracts for Annual Meeting of the Mineralogical Society of Japan, k08-09 (in Japanese).
•  Tsuchiyama,  A. (2017) Jadeite: The national stone of japan. Elements, 13, 51.
•  Tsujimori,  T. (1998) Geology of the Osayama serpentinite melange in the central Chugoku Mountains, southwestern Japan:320 Ma blueschist-bearing serpentinite melange beneath the Oeyama ophiolite. The Journal of the Geological Society of Japan, 104, 213-231 (in Japanese with English abstract).
•  Tsujimori,  T. (2017) Early Paleozoic jadeitites in Japan: An overview. Journal of Mineralogical and Petrological Sciences, 112, 217-226.
•  Tsujimori,  T. and  Harlow,  G.E. (2017) Jadeitite (jadeite jade) from Japan: History, characteristics, and perspectives. Journal of Mineralogical and Petrological Sciences, 112, 184-196.
•  Wise,  W.S. (1982) Strontiojoaquinite and bario-orthojoaquinite: two new members of the joaquinite group. American Mineralogist, 67, 809-816.