Jadeitite, known as ‘hisui’ in Japan, has been esteemed as sacred stone in both ancient and modern Japanese cultures. Although it was thought that the source material of Japanese jadeitite was brought from China, the identification of jadeite in 1939 changed this interpretation. Japanese jadeitites and jadeite–rich metasomatic rocks are found in Paleozoic and also Mesozoic geotectonic units. All localities are situated in serpentinite mélange with high–pressure metamorphic rocks and/or serpentinite lenses within a high–pressure metamorphosed complex. Outcrop exposures of contact between jadeitite and host serpentinite are extremely rare. Normally the jadeitites show lithological heterogeneity in the same locality due to multiple deformation, recrystallization, and metasomatic fluid infiltration. Studies over the last two decades have interpreted jadeitite in worldwide either as the direct aqueous fluid precipitate (P–type) from subduction channel into the overlying mantle wedge, as the metasomatic replacement (R–type) by such fluids of oceanic plagiogranite, graywacke, or metabasite along the channel margin, or a combination of these two processes. Japanese jadeitites are classified into one or the other type. Multiple stable isotope characterization analyses for jadeitite and related metasomatic rocks and serpentinite become increasingly important to decode fluid behaviors in past subduction zone. However, available geochemical data on Japanese jadeitite are very limited in comparison with other studied localities. More systematic research will unlock new insights about fluid flow and its impacts at the bottom of forearc mantle where jadeitites form. Chemical differentiation and transportation of the fluids involved in jadeitite–formation are crucial topics requiring further research. Nevertheless, the designation of jadeite (and jadeitite) as the national stone of Japan by the Japan Association of Mineralogical Sciences in 2016 should bolster education of the public about this revered stone and its role in subduction zone processes.

The Nishisonogi jadeitite is a peculiar example among Japanese jadeitites in terms of the age of formation and its genesis as metasomatic replacement (R–type). The Nishisonogi jadeitite is characterized by jadeite with a quartz–inclusion–rich core and quartz–free rim. The pressure–temperature (P–T) conditions of the Nishisonogi jadeitite is constrained by the assemblage of jadeite + quartz and of clinozoisite + paragonite + quartz. The jadeitite occurs as tectonic blocks in a sepentinite mélange together with metasomatic rocks such as omphacitite, albitite and zoisite rock. The protolith of the jadeitite is likely plagiogranite or adakitic granite as suggested by the rare earth element (REE) pattern of zircon. The zircon has a euhedral core with a U–Pb age of 126 ± 6 Ma with exhibiting sharp and flat boundary with metamorphic rim, which has a U–Pb age of 84 ± 6 Ma. The rim age is almost consistent with the 95–90 Ma age of the peak metamorphism of the coherent schists, as a host of the serpentinite mélange, as determined by ⁴⁰Ar/³⁹Ar method applied to glaucophane and phengite. Some jadeitite blocks show lithological zonations with albitite and other rocks in scale of several tens of centimeters. These zonations likely formed in the stability field of albite during exhumation of the serpentinite mélange. The isocon analysis of whole rock compositions and the singular value decomposition analysis of mineral reactions show that SiO₂, Na₂O, and Fe₂O₃ evolved from the jadeitite towards serpentinite according to the retrograde reactions.

Paleozoic jadeitite–bearing serpentinite–matrix mélange represents the oldest mantle wedge record of a Pacific–type subduction zone of proto–Japan. Most jadeitites are fluid precipitates (P–type), but some jadeitites are metasomatic replacement (R–type) which preserve relict minerals and protolith textures. The beauty and preciousness of some gem–quality, semi–translucent varieties of jadeitites in the Itoigawa–Omi area led to the designation of jadeitite as the national stone of Japan by the Japan Association of Mineralogical Sciences. Zircon geochronology indicates jadeitite formed prior to Late Paleozoic Renge metamorphism that formed blueschist and rare eclogite. For example, in the Itoigawa–Omi and Osayama localities, older jadeitites and younger high–pressure/ low–temperature metamorphic rocks in a single mélange complex imply different histories for the subduction channel and jadeite–bearing serpentinite–matrix mélange. This suggests that the jadeitite–hosted mélange (or serpentinized peridotite) can stay within the mantle wedge for a considerable time; thus recrystallization, resorption, and re–precipitation of jadeitite can continue in the mantle wedge environment. Therefore, studies of Paleozoic jadeitites in Japan have great potential to elucidate the earliest stages of orogenic growth (oceanward–accretion and landward–erosion) associated with the subduction of the paleo–Pacific oceanic plates, and to test geophysical observations of modern analogues from a mixture of fossilized mantle wedges and subduction channels.

This paper presents a review of Itoigawa’s jadeitite in history, culture, process of rediscovery, and geological characteristics. The people of the Jomon age used jadeitite as tools as far as 7000 years ago, making it one of the oldest jadeitite cultures in the world. The jadeitites from Itoigawa were the source of ornaments such as pendants or comma–shaped beads that can be dated to the Jomon age through to the Nara period. These ornaments are widely found in Japanese Islands from Hokkaido to Okinawa Prefecture, and also in the southern part of the Korean Peninsula. The jadeitite, however, was not used after the Nara period. The disappearance of jadeitite culture is not well understood, but it may have been caused by the introduction of Buddhism into Japan. Therefore, the existence of jadeitite in Japan was forgotten for a period of 1200 years after the Nara period. Mr. Eizo Ito rediscovered jadeitite from Itoigawa when he identified the durable green rock in the Kotakigawa River in 1938. His success was inspired by the idea of Mr. Gyofu Soma. The rediscovered jadeitite was studied by Dr. Yoshinori Kawano of the Tohoku Imperial University in 1939. There are large jadeitite boulders weighing more than 100 tons found in several areas of the Kotakigawa and Ohmigawa Rivers. These areas are designated national natural monuments. The jadeitite from Itoigawa can be found in various colors such as white, gray, black, lavender, and blue. These color variations are caused by the presence of trace elements such as iron and titanium in jadeite and omphacite, and tiny graphite inclusions in jadeitite. The absence of quartz and euhederal jadeite crystals with natrolite and veinlets of jadeitite indicates that the Itoigawa jadeitite does not form through decomposition of albite, but by hydrothermal activity. Some strontium dominant minerals such as itoigawaite were first found in jadeitite from Itoigawa. These strontium dominant minerals form in the calcium depleted hydrothermal solution in the late stages of jadeitite formation. The Jomon is the oldest jadeitite culture worldwide, and the first documented use of precious stones in the history of mankind. In addition, the jadeitite found in Itoigawa is the oldest known unit of its kind.

The mode of occurrence of jadeitic pyroxenes and their origins were reviewed using literatures published in the Sanbagawa belt (sensu lato), SW Japan, and the Kamuikotan belt, Hokkaido. Jadeite + quartz assemblage is found from tectonic blocks both in the Yorii area of the Kanto Mountains in the Sanbagawa belt and the Kamuikotan Gorge area, and its formation timing is predated to the main metamorphism in each area, where albite is stable along with metamorphic pyroxenes with lower jadeite contents (namely Jd_<50). The jadeite + quartz assemblage is recently found as inclusions in garnet grains in some rocks with peculiarly lower CaO and/or MgO bulk compositions, which suffered the eclogite facies metamorphism in the Sanbagawa belt of Shikoku area, although it is not detected from the matrix of the eclogite facies rocks. Recent zirconology applied to the jadeite + quartz rock in the Yorii area causes a hot argument on its origin, i.e., the wholesale metasomatic replacement origin or the vein precipitation origin. In either case, this methodology gave new insight on fluid activity recorded in Jurassic or post–Jurassic subduction zone.

Jadeite occurs as the shocked product of albite feldspar in shocked meteorites, and is one of the most common high–pressure polymorphs in shock–melt veins of meteorites. The characteristic textures of jadeite in shocked ordinary chondrites show that some of jadeite crystals were formed from originally albite feldspar by a solid–state transformation and some were crystallized from a shock–induced albite melt. Based on these textures of jadeite together with the other high–pressure mineral assemblages and their crystallization kinetics, we can estimate the impact conditions such as impact velocity and parent–body size.

Omphacite replacing after relic edenitic pargasite has been found in an omphacite–bearing jadeitite block of the Itoigawa–Omi area in the Hida–Gaien belt. Omphacite occurs sporadically as fine–grained aggregate reaching a few cm in length in a jadeite–albite matrix, and sometimes contains edenitic pargasite as a core. The edenitic pargasite is chemically and optically homogeneous and does not show direct contact with jadeite and albite. An irregular shaped omphacite–diopside mixed area occurs near edenitic pargasite in a coarse omphacite aggregate. The texture suggests that the breakdown of edenitic pargasite was triggered by the addition of a hydrothermal fluid, from which jadeite and albite were precipitated later, passing through diopside and omphacite by the reaction:

At the periphery of pseudomorphic omphacite, a hydrothermal fluid removed the breakdown components of the reaction other than omphacite.

 New in–situ LA–ICP–MS U–Pb dating revealed that zircons in edenitic pargasite yield apparent age up to ~ 590 Ma, with mean ages of 560 ± 16 Ma, interpreted as the minimum age of a precursor rock. A zircon age of 519 ± 21 Ma from jadeitite without omphacite corresponds to a timing of crystallization of omphacite, jadeite, and albite. The studied jadeitite is a typical R–type jadeitite, and the nearly total replacement from a precursor rock to the omphacite–bearing jadeitite has been attributed to hydrothermal activity at Middle Cambrian times.

Jadeitite from the Itoigawa–Omi area in the Hida–Gaien belt is hydrothermal in origin, occurring as tectonic blocks in a serpentinite mélange. Most jadeitite shows bimineralic mineralogy essentially composed of jadeite and albite without quartz. It sometimes has veins and cavities filled with zeolite–bearing assemblages of natrolite–jadeite and analcime–jadeite. In veins and cavities, jadeite often shows euhedral shapes in natrolite and analcime matrices and accompanies Sr–Ti–Zr–bearing new minerals such as itoigawaite, rengeite, and matsubaraite. Phase relation in the NaAlSiO₄–SiO₂–H₂O system has been analyzed based on the Schreinemakers’ rule to explain the hydrothermal origin of these jadeitites and the euhedral form of jadeite. The albite– and natrolite–jadeitites were precipitated from a hydrothermal fluid in the pressure–temperature field surrounded by the following four reactions: 1) albite = jadeite + quartz, 2) natrolite = nepheline + jadeite + 2 water, 3) natrolite + albite = 3 jadeite + 2 water, and 4) analcime = jadeite + water. Jadeite and analcite seem to be in equilibrium because of their euhedral shapes, but never crystallize from a fluid phase in the NaAlSiO₄–SiO₂–H₂O system. To explain the presence of euhedral jadeite in an analcime matrix, we propose two possible interpretations: 1) that the introduction of evolved, multicomponent, hydrothermal fluid becomes the fluid–analcime–jadeite triangle and appears in a pseudo–ternary system and 2) that hydrothermal fluid was present in an amount insufficient to form a water–saturated, analcime–bearing assemblage.

Jadeite–quartz rocks from the Yorii area, the Kanto Mountains, central Japan occur as tectonic blocks within serpentinite mélange. Primary two–phase (liquid + vapor) aqueous fluid inclusions are observed in jadeite, quartz, albite and zircon. The fluids trapped in jadeite and quartz are H₂O with and without CH₄ and show a wide range of salinity (4.7 ± 1.1 wt% NaCl_eqv in jadeite; 3.4 ± 0.7 and 13.6 ± 2.0 wt% NaCl_eqv in quartz). In this study, we examined the chemical composition of fluid inclusions in quartz from jadeite–quartz rock to understand the characteristics of fluid, which related to the formation of the rocks in the subduction zone. The trace element concentrations of fluid inclusions determined with LA–ICP–MS are enriched in LILE, Li, B, HFSE and transition metals with LILE enriched and relatively HFSE depleted characteristics. These have elemental patterns similar to the HFSE–depleted fluid released from antigorite during subduction, though the orders of magnitude are different. It can be common chemical characteristics of fluid in a subduction zone. There are two possibilities of the chemical composition of the evolved fluid after the formation of jadeite–quartz rocks. HFSE from the fluid can be sequestered into jadeite–quartz rock prior to fluids moving up into a mantle wedge. This process lead the evolved fluids relatively depleted in HFSE and enriched in LILE. Other possibility is that the fluid has same chemical composition of fluid inclusion as the fluid is equilibrated with jadeite–quartz rocks during the jadeite–quartz formation. In both cases, fluid after the metasomatic formation of jadeite–quartz rocks can be relatively enriched in LILE and depleted in HFSE. Magmas generated in subduction zones exhibit distinctive geochemical features of LILE enrichment and HFSE depletion and this characteristic of arc magma can be explained by the behavior of HFSE during the formation of jadeite–quartz rocks.

Jadeitite from the New Idria serpentinite body of California is a fluid precipitation–to–metasomatic product. Optical cathodoluminescence (CL) microscopy of the jadeitite revealed that vein–filling ‘pure’ jadeites (mostly 97–99.9 mol% jadeite) exhibit bright luminescence, whereas ‘impure’ jadeites (mostly 75–95 mol% jadeite) in pale–greenish matrix show dark luminescence. The ‘pure’ jadeites in the veins are composed of mixtures of red, blue and dull blue CL–colored domains, showing growth textures (oscillatory bands). The ‘impure’ jadeites in the pale–greenish matrix with dark luminescence have a higher augite component (up to 5.37 wt% FeO), implying that the CL property is due to significant amount of Fe²⁺ to act as a quencher. CL spectra of the blue CL–colored domains of the vein–filling ‘pure’ jadeite have a doublet broad emission peak centered at ∼ 320 and ∼ 360 nm in the ultraviolet (UV) to blue region. In the red CL–colored domains, a broad asymmetric emission peak at ∼ 700 nm is also recognized together with the doublet UV–blue emission peak. Comparing monochromatic CL images in the UV–blue (300–400 nm) and red (650–750 nm) emission regions with X–ray elemental maps, luminescence centers contributing the UV–blue and red CL emission peaks were assigned. The red emission peak of the ‘pure’ jadeite with subtle augite component would be attributed to lattice defects related to Ca²⁺, Fe²⁺ (or Fe³⁺) and Mg²⁺ deficiency and/or excess centers in M1 or M2 sites. Alternatively, transition metal ions (Mn²⁺ and Fe³⁺) or rare earth elements in the M1 and M2 sites as impurity centers, might contribute to the red emission peak. As the UV–blue emissions correlate with Al³⁺ content, i.e. purity of jadeite component, they might be related to Na⁺ and/or Al³⁺ defect centers.

The density of the jadeite (NaAlSi₂O₆) melt has been measured up to 6.5 GPa and 2273 K using the X–ray absorption technique at beamline 13–BM–D of the Advanced Photon Source. A fit of the pressure–density–temperature data to the high temperature Birch–Murnaghan equation of state yielded the following thermoelastic parameters: density, ρ₀ = 2.36 g/cm³, isothermal bulk modulus, K_T0 = 21.5 ± 0.8 GPa, its pressure derivative, K₀′ = 8.9 ± 1.2, and the temperature derivative (∂K_T/∂T)_P = −0.0021 ± 0.0011 GPa/K at a reference temperature T₀ = 1473 K. The densification of jadeite melt at low pressures is primarily dominated by topological changes in the structure, including a decrease in T–O–T angle and breaking and reforming of the T–O bond (T = Si⁴⁺, Al³⁺). Compressibilities of jadeite, albite, diopside, phonolite and peridotite melts display a systematic trend: the K₀–K₀′ plot of these silicate melts exhibits an inverse linear relation.