Encyclopedia of Japanese Minerals (Go to Intro Page)
by Alfredo Petrov
Minerals Starting with "J"
JACOBSITE (yakobusu-koh)
Gumma: Black jacobsite is associated with tan microfibrous wiserite eyes, surrounded by a mixture of alleghanyite and rhodochrosite, in lenses of metamorphic manganese ore at the Kurokawa mine. With hausmannite, rhodochrosite and alleghanyite, forms the dark brown bands in ore at the Yamabishi mine. Also at the Mogurazawa mine.
Kyoto: In brown granular sonolite aggregates at the Sono mine. As brown-black bads to 2mm thick in finely banded metasedimentary mangaese ore at the Ashidani mine.
Nagano: With alleghanyite, manganosite, hausmannite and rhodochrosite in high-grade, banded folded ore in meta-chert at the Hamayokokawa mine.
Osaka: Granular banded, with galaxite, and minor rhodochrosite and tephroite, at the Hirono mine.
Shiga: A significant minor component of rhodochrosite-sonolite-manganosite ore, and alleghanyite-galaxite-hausmannite ore, at the Ioi mine. Some magnetic grains here are roughly equimolar jacobsite-galaxite, dark chocolate brown in reflected light, reddish brown in transmitted light.
Tochigi: Jacobsite is associated with jimboite in contact metasomatic banded rhodochrosite ore near a granite intrusion at the Kaso mine. The so-called "chocolate ore" here is rich in jacobsite and galaxite, sometimes also with wiserite.
Tokyo: Forms black to greenish black patches and veinlets in dark brown hausmannite ore hosted in metasedimentary chert at the Kiyokawa mine.
JADEITE (hisui-kiseki)
Fukuoka: Fukuoka? (west end of Sanbagawa belt)
Gumma: Jadeite and omphacite co-exist in a jadeite vein in low-grade metamorphic rocks in the Shibukawa area, with apparent miscibility gaps between these two pyroxenes.
Hokkaido: Light greenish grey jadeite, with pumpellyite, are the main components of metagabbro in the Kamuikotan metamorphic belt in the Kamuikotan gorge, Asahikawa, (and at Mitsuishi?). (north central Hokkaido).
Hyougo: White jadeite as short prismatic grains to 2mm is intergrown with paragonite, edenite and corundum as columnar aggregates to 5cm in albitite rock at Kabozaka. This is the 2nd largest jadeite deposit in Japan. No green jade is present here. Located in the same small metamorphic belt as the neighboring jadeite deposit in Tottori-ken.
Kouchi: Enkyohji (Engyoji).
Nagasaki: Dark grey-green jadeitite at Mie.
Niigata: Comma-shaped jadeite beads called "magatama" have been found in many prehistoric japanese tombs dating back perhaps 5,000 years (making Japan perhaps the world's oldest jadeite-using culture). But although these magatama are mentioned in ancient writings, the source of this jadeite was then forgotten for over 1,000 years (Wada even went so far as to say there was no jade in Japan) until Y. Kawano first reported the mineral jadeite from the Kotaki river and elsewhere in Itoigawa in 1939, after which a nearby locality, Hashidate, became the only commercially exploited gem jadeite locality in Japan, until the area became a national monument and further collecting was prohibited. (Commercial collecting still goes on outside the protected areas, mostly from alluvial river and beach deposits.) At Hashidate, associated with riebeckite-albite rock units in highly brecciated serpentinites of the Renge metamorphic belt. The true jadeite at this in situ locality and nearby alluvial localities (as albitite-jadeite river boulders up to 20 feet (!) across in the Kotaki river, and as cobbles on the ocean beach at Oyashirazu) varies from milky-colorless to white or green, rarely pale bluish green, blue or violet (titanian), usually translucent, but some of the most highly prized classic green "jadeite" here turns out to be largely green omphacite, with lesser jadeite component. (Jadeite and omphacite can co-exist, with an apparent miscibility gap (Jd 65<86) in Ohmi samples.) The jadeite crystals are granular to slightly elongated, anhedral, 0.5 to 3mm, forming massive aggregates, associated with albite, actinolite, magnesiohornblende, chlorite, prehnite, quartz and zoisite. Rarely, as short prismatic euhedral crystals in small vugs in massive jadeite, or embedded in analcite. Analysis of a green Kotaki river jadeite (RI 1.658-1.673) corresponds empirically to (Na 0.841, Ca 0.061, K 0.008) (Al 0.944, Mg 0.088, Fe''' 0.021, Fe'' 0.006, Ti 0.001, Mn 0.0003) (Si 2.029) (O [6], OH 0.20); a white one gave (Na 0.856, Ca 0.037, K 0.005) (Al 0.990, Mg 0.041, Fe''' 0.017, Fe'' 0.002, Ti 0.001, Mn nil) (Si 2.050) (O [6], OH 0.29) (both recalculated from old Y. Kawano analyses), indicating that green jadeite contains only slightly higher Ca-Mg-Fe'''-Fe'' (omphacite component) than white jadeite. Another analysis of Kotaki river jadeite, from a 20cm-wide jadeite-albitite zone around an albitite core, gave the formula (Na 0.828, Ca 0.058, K 0.006) (Al 0.932, Mg 0.087, Fe''' 0.020, Fe'' 0.005, Ti 0.001) Si 2 O 6; this jadeite-albitite zone is itself surrounded by edenite (qv) embedded in serpentine. Typical zoning pattern, listed outwards from the albitite core is albitite (5cm to 1m diameter), jadeite-albitite, white jadeite, green jadeite (up to 20cm), green jadeite+actinolite, serpentine. (Caveat emptor: much of the jadeite sold at the several local souvenir shops is really from Burma; local jadeite is scarce and much more expensive.)
Okayama: White to pale greyish and pale pink, compact fibrous masses of jadeite rock in greenish serpentine with rodingite at Ohsakabe. The jadeite rock is composed principally of jadeite, with subordinate grossular and analcime, and accessory prehnite, vesuvianite, natrolite, thomsonite, "deweylite", chlorite and diopside. Free-standing jadeite crystals are very rare, but occasionally found in vugs in hard parts. The jadeite crystals here are remarkably pure, from 96 to 100% jadeite molecule, up to 3% diopside. Pink zircon xls sporadically included. Cut by tiny white veinlets of analcime, grossular or stronalsite. One pumpkin-size white jadeite boulder is protected by a roof and fence as a natural monument, but shattered fragments to decimeter size are abundant in the area. Kosmochlore and uvarovite occur, but rarely, in the serpentine nearby.
Saitama: Jadeite and pumpellyite are the main components of metagabbro from the Sanbagawa metamorphic belt in Chichibu.
Tottori: In the Sangun metamorphic belt, at Tsunodani in Wakasa-cho, jadeitite boulders are mined for decorating shrine gardens and for lapidary work. The jadeite is white to pale bluish grey to light violet ("lavender jade"), and is associated with grossular, rutile and white rectangular zircons to 2mm.
JAHNSITE-(CaFeFe) (jahnsu-seki)
Hyougo: The type locality for this extremely rare phosphate, known from only a single specimen, is a Seishin-Chuhou roadcut at Oshibedani in Kobe city, where it occured as multiple euhedral microcrystals in a cockscomb-shaped aggregate together with ushkovite in a small vug in the center of a single 3cm diameter vivianite nodule from a Pliocene-Pleistocene clay bed. Other associated species are earthy mitridatite, furry beraunite and sprays of rockbridgeite. Like most roadcuts in Japan, this has now been covered with a concrete erosion-control barrier and so is inaccessible. (No relation to any phosphate pegmatite.) Minor Mn,Mg,Al are also present, with the empirical formula Ca 0.6 Mn'' 0.6 Fe'' 1.9 Mg 0.8 Fe''' 1.9 Al 0.1 (PO4)4 .10H2O - dark brown color, vitreous-adamantine luster.
"JAPANITE"
Ouita: A beautiful pale green vitreous mineral, associated with chromite in serpentine from the Washidani chromite deposit was named "japanite" in 1882. The original analysis, apparently unreliable, suggested that japanite was a hydrous Mg-Al-K-Cr-oxide, but it was also reported as "uvarovite" and "chromium ocher". Later more reliable analysis gave an empirical formula of (Mg 2.48, Fe'' 0.13, Ca 0.04)2.65 (Al 0.68, Fe''' 0.10)0.78 Si 1.57 O [5] (OH)4.17, which could correspond to clinochlore or a serpentine-group species. (The density would be closer to clinochlore, and J. Shinoda has suggested the material is the clinochlore variety "penninite".) These apparently isometric green cloudy spots in the matrix are seen under the microscope to consist of minute fibrous crystals, and they may represent a pseudomorph of serpentine or clinochlore after an isometric mineral (magnesiochromite?). (H 3.5; D 3.08; conchoidal fracture.)
JAROSITE (tetsu-myohban-seki)
Gumma: Layers of jarosite constitute 20% of the Pleistocene limonite ore at the Gumma iron mine. These limonite-jarosite layers fill an old stream bed 2 km long, 10m deep and 30m wide. Abiotic deposition by springs related to volcanism. Some of the jarosite forms sharp blocky or equant crystals.
Hokkaido: A component of the sedimentary "limonite" or "bog iron" ores at several iron mines, where it was deposited by Pleistocene springs related to volcanic activity. At the Nippou mine and the Utro mine.
Kumamoto: In Pleistocene limonite ore of the Aso iron mine.
Kyoto: Lustrous dark brown triangular crystals at Gyohjayama.
Nagano: Phosphatian jarosite (4.54 wt% P2O5) is a major ore mineral in a Pleistocene limonitic ore bed at the Suwa iron mine, sometimes in vugs associated with tinticite, konickite or other phosphates. Precipitated on Yatsugatake andesitic lava and pyroclastics by a volcanogenic acid hot spring. (Sakurai et al. (1987) Bull. Nat. Sci. Mus., ser. C, 13, 149-156)
JENNITE (jenni-seki)
Hiroshima: Kushiro.
Okayama: Parallel or radial aggregates of white, vitreous, acicular crystals to 0.2mm long forming fissure-filling veinlets to 3mm wide in fractured spurrite rock at Fuka, the first japanese locality for this species. Apparently an alteration product of afwillite and spurrite. For a width of 2 or 3cm around these veinlets, the spurrite is altered to foshagite, scawtite, xonotlite and calcite. Jennite is also found filling thin fissures in afwillite, and along the contact between oyelite and afwillite, and in mixtures of foshagite and calcite with minor scawtite in an alteration zone around a fluorite-prehnite vein in spurrite rock. Difficult to distinguish visually from tobermorite, oyelite and bultfonteinite.
JIMBOITE (jinbo-seki)
Fukui: Fujii mine.
Gunma: Brown jimboite occurs at the Ritoh mine, as bands in massive banded metasedimentary manganese ore.
Tochigi: The type locality for this manganese borate is the 18th level of the Kaso mine, where it was found as light purplish brown, vitreous, anhedral crystals to 5mm, exhibiting one perfect cleavage direction (110) and a parting on (101), in contact metasomatic banded rhodochrosite ore near a granite intrusion. Jimboite is of relatively large grain size compared to its associated species: rhodochrosite, galaxite, jacobsite, tephroite, sonolite, wiserite, alabandite, galena, pyrrhotite, chalcopyrite. Minor magnesium and iron replace divalent manganese - (Mn 2.67, Mg 0.23, Fe 0.06). (RI 1.792 - 1.821; colorless in thin section; H 5.5.) A second locality in Tochigi-ken has been discovered recently by field collectors.
JOHANNSENITE (yohansen-kiseki)
(The best japanese blue johannsenite might be the world's most beautiful, and enjoys minor use as a lapidary material for small cabochons.)
Fukui: Ferroan johannsenite as pale greenish grains around 0.2mm diameter, with pale pink bustamite, forms skarn with Zn-Pb-sulfides in the Nakayama orebody of the Nakatatsu mine. Two analyses gave (with % hedenbergite and diopside molecules) Jo 53, He 40, Di 7; Jo 51 He 40, Di 9. In central skarn zones, grades into Mn-rich hedenbergite.
Niigata: Compact aggregates of bluish green divergent columnar crystals to 8cm from the Akadani iron mine.
Okayama: Brown to grey-green or pale bluish, compact fibrous radiating masses at the Ohnagusa mine.
Shizuoka: Bluish, with inesite and other pink manganese ores at the Kawazu gold-silver mine. Sky-blue johannsenite masses to 12cm at the Yugashima mine.
Yamanashi: Associated with braunite, caryopilite and pumpellyite-(Mn) at the Ochiai mine, in Mn ore.
JOHNBAUMITE (jonbaumu-seki)
Okayama: With okayamalite and pentahydroborite in pyrometasomatosed marble at Fuka. Also here with calcite, andradite, arsenopyrite and loellingite in a vein cutting marble near a skarn zone. Hydrothermally altered to cahnite (qv).
JOKOKUITE (johkoku-seki)
Hokkaido: The type locality for this hydrous manganese sulfate is the Johkoku mine, where it forms beautiful pale pink stalactites to 10 cm long on gallery walls, deposited from room-temperature acid mine waters which had dissolved rhodochrosite vein gangue. Associated species include gypsum, szmikite, ilesite, rozenite, siderotile, ferrohexahydrite, mallardite, melanterite and goslarite. Also at the Inakuraishi mine.
JONASSONITE (IMA 2004-031)
Kagoshima: Jonassonite, AuBi5S4, occurs as grains in Au-Bi-W-bearing quartz-tourmaline veins in Mesozoic slate near the Miocene Takakumayama granitic intrusion at the Tsugahira (Togahira) mine. Light greyish white in polished section. Hardness similar to that of "joseite" (harder than bismuth). Closely associated with native bismuth, joseite-A and joseite-B, all of which formed later than the original wolframite, arsenopyrite, pyrite, quartz and tourmaline.
JORDANITE (yorudan-koh)
Aomori: At the Yunosawa mine, as metallic black multi-cm botryoidal aggregates composed of 1 to 3mm spheroids, in kuroko-type barite-bearing quartz veins in Miocene breccia tuff. In 1925, some jordanite from here was erroneously described as the new species "RENIFORITE", named for its reniform habit (greyish-white metallic; black streak; D 6.451; with 0.45 wt% Fe). Also as thin mm-wide bands of massive jordanite along the edge of a vuggy galena-barite vein, rarely in vugs as aggregates of minute crystals. Also as pseudomorphs after microscopic tsugaruite aggregates. Also at the Okoppe mine.
JULGOLDITE-(Mg) (kudo-jurugorudo-seki)
Mie: The type locality of this pumpellyite-group species is Toba, Shinsen-mura. Green, with "submetallic" luster. (Note that the closely related species pumpellyite-(Mg) (qv) also occurs here.)
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