Discovery of New Mineral "Amaterasu Stone" ─ A Titanosilicate Named After Japan's "Sun Goddess" Found in Jade from Niimi, Okayama Prefecture

Introduction: Context for Foreign Readers

In Japan, jade culture has flourished in various regions, including Itoigawa, and in 2016, it was designated as **"Japan's National Stone". The newly discovered mineral is an academic achievement "originating from Japan", found in the symbolic jade. The discovery site is **Osa Mountain area, Niimi City, Okayama Prefecture. The paper was published on August 7, 2025, and the research team includes members from the University of Tokyo, Kyoto University, Yamaguchi University, JASRI (SPring-8), and Rigaku. The news was reported by major domestic media on August 7-8. For foreigners exploring Japanese culture and geology, this discovery offers a unique intersection of **mythology (Amaterasu) × crystallography (structural duality)**. Japan Association of Mineralogical SciencesJ-STAGEMynavi NewsITmedia

1. What Was Discovered: The Identity of Amaterasuite

• Mineral Name: Amaterasuite

• Ideal Chemical Formula: Sr₄Ti₆Si₄O₂₃(OH)Cl

• Crystal System: Orthorhombic (Space Group Fddd)

• Mohs Hardness: 6

• Calculated Density: Approximately 4.0 g/cm³

• Pleochroism: Blue to brown under parallel Nicol (single polarization)

• Occurrence: Needle-like to plate-like crystals aggregated in bundles around rutile (up to 150 µm)

• Color: Reported as deep green (based on samples and literature)

• Type Specimen: Deposited at the National Museum of Nature and Science (NSM M-52596)

• IMA Approval Number: 2024-056

• Type Locality: Osa Kosakabe, Osa Mountain, Niimi City, Okayama Prefecture (Coordinates: 35°05'38"N 133°33'01"E)
  These properties are based on the abstract of the peer-reviewed paper and mineral databases. J-STAGEResearchGatemindat.org
  
  

2. Why "Amaterasu"? Naming and Japanese Culture

The naming reflects respect for Japan's stone culture and the symbolism of the duality in crystal structure. Amaterasu, the sun goddess, is said to have a dual nature of "Aramitama" and "Nigimitama", and Amaterasuite also features two structural elements, Type A/B, coexisting within its unit cell. This naming, which overlaps the "duality" of mythology and crystallography, can be considered a distinctly Japanese naming. Japan Association of Mineralogical SciencesJ-STAGE

3. Where and Who Discovered It: Jade in Niimi, Okayama, and the Research Setup

The discovery site is a jadeite rock body in the Osa Mountain area. According to the occurrence description, it was found near the boundary with serpentinite, within a jade block of about 1 meter, associated with prehnite-rich parts. The authors are affiliated with the University of Tokyo (Institute for Solid State Physics), Kyoto University, Yamaguchi University, JASRI, and Rigaku, with analysis using SPring-8's synchrotron powder X-ray diffraction. ResearchGate

4. Highlights of the Crystal Structure: First Demonstration of "A/B Duality"

The structure of Amaterasuite is identified as amaterasuite-4O, with Type A and Type B coexisting within the unit cell. The occupancy is estimated at A: about 85% / B: about 15%. This is the first confirmation of a theoretically predicted structural motif in a real specimen, adding a new example to the diversity of existing crystal structures, which is its greatest academic significance. The space group is Fddd, with lattice constants
a = 5.85558(2) Å, b = 20.43960(8) Å, c = 33.28240(12) Å, V = 3983.43(3) ų (Z = 8). J-STAGE

5. Key Points of Chemical Composition and Physical Properties: Strontium-Rich Titanosilicate

The empirical formula (23 O + 2(OH,Cl) basis) is
(Sr₃.₃₂Ba₀.₆₄)Σ₃.₉₆ (Ti₅.₇₃Fe₀.₁₆Nb₀.₀₂)Σ₅.₉₁ Si₄.₁₅ O₂₃ (OH)₀.₉₅ Cl₁.₀₅,
and the ideal formula is Sr₄Ti₆Si₄O₂₃(OH)Cl. Physical properties reported include pleochroism (blue→brown), hardness of 6, brittleness, and calculated density of 4.0 g/cm³. The color is described as deep green in literature and specimens, consistent with the orthorhombic Fddd. J-STAGEmindat.org

6. The Science of "National Stone Jade": Why New Minerals Emerge in Japan

Jadeitite forms in the low-temperature, high-pressure environment of subduction zones, often accompanied by Sr-rich accessory minerals. The Japanese archipelago is located in a cold temperature gradient subduction zone, fostering not only jade culture but also mineralogically unique host rocks. In jade bodies such as those in Itoigawa (Niigata), Wakasa (Fukui), and Osa Mountain (Okayama), new Sr-based titanosilicate minerals like rengeite, matsubaraite, and itoigawaite have been reported, and the discovery of Amaterasuite follows this lineage. ResearchGate

7. Research Methods and Verification: The Power of SPring-8 × Powder XRD

In this study, synchrotron powder X-ray diffraction (SPring-8) played a key role in precise structural analysis. Rietveld refinement using numerous large d-value peaks (80 peaks) confirmed lattice constants and space group. The occupancy of A/B duality (about 85/15%) was also estimated. For elemental distribution in a wide field and identification of microphases, a comprehensive approach including powder XRD, electron microprobe analysis (EPMA), and optical observation was effective. The paper reports a micro occurrence of **bundled crystals around rutile (150 µm class)**. J-STAGE

8. The Intersection of Culture and Science: The Narrative of "Amaterasu"

The name of Amaterasu, the sun goddess, reflects a respect for the mythological world connected to Japan's oldest historical texts, **'Kojiki' and 'Nihon Shoki', and the cultural asset of national stone jade. The narrative of naming, where the duality of crystal structure and the duality of Aramitama/Nigimitama of Amaterasu resonate, is an excellent example of science communication, likely to be memorable to international readers. Japan Association of Mineralogical Sciences

9. Significance for Earth Sciences: "Strontium-Titanium Chemistry" in Subduction