Encyclopedia of Japanese Minerals (Go to Intro Page)
by Alfredo Petrov
Minerals Starting with "I"
IIMORIITE-(Y) (iimori-seki)
Fukushima: The type locality for this rare yttrium silicate-carbonate is Fusamata, where it forms light purplish grey or tan masses up to 3x3x2cm size, with vitreous to resinous luster and one distinct cleavage direction (011), associated with orthoclase, biotite, fergusonite, monazite and uraninite, in a quartz-microcline pegmatite. Originally described as Y-Mg-silicate-hydroxide, only later was it discovered that the volatile component was carbonate, not water. Analysis shows only minor substitutions in the range 0.7 to 1.4 wt% oxides: Zr, Fe''', Al, phosphate, U, Ca, Ce group REE, Mg, and very minor Th (0.11%). (H 5.5-6; D 4.21; streak white with purplish grey tint; colorless in thin section; RI 1.786 - 1.827.) Also found nearby at Suishouyama (formerly Iisaka) pegmatite, as an alteration of thalenite.
IKAITE (ika-seki)
Hokkaido: Ikaite forms in winter around the edges of saline springs at Shiowakka. Dehydrates irreversibly to calcite when the temperature rises. (Vaterite is also reported from here.)
(Specimens labelled "ikaite" (or "gennoh-ishi) from Fukushima, Nagano and Niigata prefectures are actually calcite (qv) pseudomorphs after ikaite.)
IKUNOLITE (ikuno-koh; hose-koh-A)
Hyougo: Lead-grey platy xls, ranging from microscopic to about 1mm diameter (although multi-cm plates are also alleged), very flexible, showing only (0001) faces and cleavages, usually coated with bismuthinite (or the reverse, ikunolite coating Bi minerals) and intimately associated with bismuth, ferberite, chalcopyrite, pyrite, secondary Bi minerals and sporadic cassiterite in a high-temperature vein of fine-grained massive grey quartz in the Kanagase orebody of the Ikuno mine, the type locality for this rare bismuth sulfide of the tetradymite group. The host rock for these polymetallic veins is Cretaceous pyroclastic rhyolite. Contains 1.98% Se, corrsponding to a formula Bi 3.90 (S 2.84, Se 0.26). (Streak dark grey; H 2; D 7.8; stains grey in conc. HNO3, bluish grey in 1:1 HNO3.) Cleavages to 2.5cm(!) across have come from the Akenobe mine.
ILLITE (iraito; kasui-shiro-unmo)
Aichi: Fine-grained "sericite" is mined for cosmetic purposes at the Iname (Furikusa) mine. (muscovite??????)
Ibaragi: A compact pale violet-pink illite from Myohkensan is used to cut cabochons for rare gem collectors.
Okinawa: Illite and halloysite (not kaolinite) are the dominant clay minerals in the "Oku red soils" of Okinawa Island.
Shimane: Greenish "sericite clay" mined at the Unnan mine contains both Mg-rich illite and Fe-rich illite. Analyses correspond to the empirical formulae: (K 1.55, Na 0.27) (Al 2.97, Mg 0.55, Fe'' 0.18, Fe''' 0.05, Ca 0.05, Ti 0.02, Mn'' 0.01) (Si 6.04, Al 1.96) (OH) 5.44 ("magnesium sericite"), and (K 1.63, H3O+ 0.44) (Al 3.02, Fe''' 0.59, Fe'' 0.17, Ca 0.16) (Si 6.36, Al 1.64) (OH) 4, including 0.89 wt% SO3, ("iron sericite"), (Minato & Takano, 1952; in DHZ). "Hydromuscovite" at the Matsushiro mine.
ILMENITE (chitan-tekkoh)
Ehime: Lamellar crystals to 5mm at Irazuyama. In Al-Ti-Fe-rich skarn in marble bed on Myoujin island, with vesuvianite and sadanagaite.
Ibaragi: At Hanazonoyama in pegmatite with andalusite.
Iwate: Analysis of "manganese ilmenite" from Teragi gave (Fe'' 1.159, Mn'' 0.601, Mg 0.008) (Ti 1.787, Fe''' 0.439) O 6 (Omori & Hasegawa, 1955; in DHZ). Also at Hashino.
Kouchi: Niobian and zincian ilmenites in syenite at Ashizuri-misaki.
Kyoto: At Ohmiya. (Also reported from "Kawabe" -Raman database)
Mie: Several thousand tons of ilmenite were extracted from the Nabari mine in the late 1950s. The ore, containing 47 to 49% TiO2, is residual ilmenite derived from decomposition of ilmenite-bearing gabbro with 5 to 6% TiO2. Intergrown with ferrian chromite (qv) and chromian magnetite in the Asama-gatake layered intrusion, in altered peridotite.
ILMENORUTILE (irumenoruchiru)
(Perhaps ought to be considered just a niobium-iron-rich variety of rutile.)
Fukushima: Ilmenorutile, discovered in 1935 in a pegmatite vein in granite at Teshirogi, was described in 1936 as "TESHIROGILITE", a name still seen on some old labels. Drs. Kimura and Ikawa correctly identified it in 1937. Fairly sharp prismatic black crystals to 3.4cm (Sakurai collection), elongated on b, are dominated by a(100) and s(111) faces, with lesser m(110) and h(210), rarely showing low pyramidal or short prismatic forms, with contact twinning on (101). Powder XRD pattern resembles rutile. Analysis gave (as wt% oxides) Ti 44.82, (Nb,Ta) 34.61, Fe'' 13.20, Al 4.48, Sn 1.61, Ca 0.43, Mg 0.21, Si 0.06, Mn'' nil, water 0.71. Associated with garnet, monazite, zircon, xenotime, tourmaline, feldspar. (Pleochroic brown, dark bluish brown; streak brownish black; D 4.778.) Also in pegmatite at Uzumine.
Kouchi: Ashizuri-misaki.
ILSEMANNITE (ai-suien-ka) (the "ai" kanji ideogram here = "indigo")
Kagoshima: Quite abundantly as coatings of "molybdenum blue" on several square meters of volcanic rubble around high-temperature fumaroles in the crater of Iwo-dake on Satsuma-Iwojima. Deposited at temperatures around 180 - 340 C.
Shimane: Reported from the Iishi mine (needs confirmation).
ILVAITE (keikai-tekkoh)
Fukuoka: At Yanagigaura, cavities in a green contact metamorphic rock hold columnar crystals with very small c-faces.
Fukushima: Reported as a possible constituent of a babingtonite-bearing hedenbergite-garnet-chalcopyrite-magnetite skarn by a granodiorite contact at the Yaguki mine.
Gifu: Beautiful shiny black, terminated prismatic ilvaite crystals to 25mm long and 1cm thick, vertically striated, occur at the Kamioka mine in a quartz-calcite-apophyllite vein crossing a hedenbergite skarn (Mokuji-type ore) which is partially altered to actinolite. These xls display the typical (110), (120), (101) and (111) as major faces, sometimes with tiny (021). Also as isolated pseudo-octahedral microcrystals. Also at the Horado mine.
Mie: Prismatic ilvaite grains to 0.2mm are disseminated in mats of chrysotile and fibrous diopside which replace olivine in serpentinized peridotite in the Asama-gadake layered intrusion, Mikabu greenstone belt. Associated with magnetite-chromite, ilmenite, anhedral andradite and prismatic diopside (qv). (An unusual environment for ilvaite, which is more usually found in skarns.) The ilvaite composition is close to the ideal, but contains 1.7 to 2.2 wt% MgO and 1.9 to 2.5 wt% MnO.
Niigata: At the Kusakura mine, black prismatic xls, sometimes coated with calcite, occur in cavities in massive ilvaite, associated with green quartz in actinolitized hedenbergite skarn. Also at the Hideya mine as short prisms to 1cm in a contact iron deposit, showing the same faces as at the Kamioka mine.
Ouita: Black crystals up to 3.5cm long, 0.5cm thick, form divergent groups embedded in skarn at the Obira mine. (Associated with tourmaline and quartz??) Excellent crystals also come from Kiura.
Yamaguchi: Crystals in contact metamorphic ore at the Nagawa deposit. In cobaltite(qv)-bearing skarn at the Naganobori mine. Massive ilvaite at Zohmeki, with cavities lined by tiny drusy crystals showing very small c- and e-faces. Also at the Kitabira mine.
IMOGOLITE (imogo-seki)
Iwate: As macroscopic gel films in the interstices of weathered pumice grains in glassy volcanic ash in Kitakami-shi.
Kumamoto: The type locality for this phyllosilicate is Ue-mura, although it has also been recognized elsewhere in the Hitoyoshi basin and is widespread at many other localities in Japan as a major constituent of soils derived from decomposed pumice. Imogolite forms white to light brown, friable earthy mixtures with feldspar, allophane, quartz, cristobalite, gibbsite, vermiculite, "limonite" and residual glass. Rounded fragments of relict pumice to several mm are often still clearly visible. The name derives from "imogo", a japanese soil type composed of brownish yellow decomposed volcanic ash. Microscopically, shows brittle masses with conchoidal fracture, vitreous, resinous or waxy luster, composed of minute bundles of colorless threadlike particles which, by electron microscopy are seen to be tubular(!), with diameter about 20 to 300 angstroms, oriented parallel to the grain boundaries of the volcanic glass. Isotropic, RI 1.47-1.51, H 2-3, D 2.63-2.70. Since there are no good analyses, and the crystal structure has not been determined, some mineralogists consider imogolite to be merely a variety of allophane, but imogolite is crystalline whereas allophane is amorphous. XRD: d-lines 1.40 (100), 2.32 (80b), 3.75 (80b), 4.12 (100), 7.8 (80b), 11.7 (80b), 21.0 (100b).
Tochigi: As macroscopic gel films in the interstices of pale brown to cream-colored decomposed pumice lapilli to 13mm in pumice soils in the Kanumatsuchi bed at Fukaiwa, and similarly at Yahadatai, both in Kanuma city. Likewise in nearby Imaichi city.
INCAITE (inka-koh)
Ouita: As heterogenous, polycrystalline aggregates rimming galena at the Houei mine. Also as "hair-like masses" in a kutnohorite matrix.
INDIALITE (indo-seki)
Toyama: "Indialite" is reported from a cordierite vein cutting polymetamorphosed pelites in the Unazuki schists near Unazuki-machi, with andalusite, sillimanite, biotite and quartz. Microprobe analysis, however, gives the empirical formula (Fe'' 1.07 Mg 0.88 Na 0.07 Mn 0.03)2.05 (Al 2.06, Si 0.95) (Al 2, Si 4) O 18, which would seem to be the as-yet-undescribed Fe-analogue of indialite, i.e. the high temperature dimorph of sekaninaite.
INESITE (inesu-seki)
(Japanese inesite occurs most often in epithermal Au-Ag-quartz veins in Tertiary volcanics, but is also known from metasedimentary Paleozoic Mn ore. Although it starts out pink, it alters to brown, blackish or white(!) on exposure.)
Hokkaido: Tiny inesite needles form botryoidal aggregates, associated with rhodochrosite, opal or acanthite in epithermal Au-Ag-bearing quartz veins at the Todoroki mine, type locality for todorokite, to which the inesite decomposes.
Shizuoka: Light rose-pink inesite is abundant as fibrous sheaves, sprays and radial spherulitic aggregates of acicular to filiform crystals to 1cm long, associated with rhodochrosite and neotocite in cavities in epithermal gold-silver-bearing quartz veins, and as pale pinkish massive-acicular inesite veins to 1cm wide, associated with johannsenite in the country rock of the Rendaiji (Kawazu) mine, the first japanese locality for inesite. Composition (as oxide wt%): Si 44.89, Mn'' 36.80, Ca 8.49, Al 0.29, Mg 0.23, Fe''' 0.18, water+ 6.89, water- 2.18 (H. Momoi analysis). Good specimens are also found in the gangue of Au-Ag veins at the Seikoshi mine and the Yagashima (Yugashima?) mine.
INYOITE (inyoh-ishi)
Okayama: A recent (2003) discovery at Fuka, as a secondary mineral in fissures of primary Ca borates (nifontovite, pentahydroborite, sibirskite, parasibirskite), formed by the action of groundwater at ambient temperatures (around 20 C). Rare sharp tabular euhedral crystals to 0.5mm, colorless to white, vitreous; more commonly as semi-compact aggregates of poorly-formed tabular crystals ranging from micro to 1mm, exceptionally 2mm. Analysis is close to the theoretical composition, with no substitutions. (D 1.875; H 2.5 - a bit harder than original description; Note: the related species colemanite and meyerhofferite are NOT present here.) (Kusachi, et al (2004) J. Min. Petr. Sci. 99, 67-71)
IRIDIUM (shizen-irijiumu)
Hokkaido: An osmium-ruthenium-bearing variety of cubic native iridium, previously known as "ruthenosmiridium" (although some of the material bearing that name is more properly ruthenium or rutheniridosmine), occurs as whitish grains in gold-platinum placers at Horokanai-cho. Also at Teshio. (See also under "osmium".)
IRON (shizen-tetsu)
Gumma: River cobbles of wehrlite (peridotite) at Mayama are traversed by veinlets of serpentine containing grains of native iron to 3mm surrounded by magnetite rims.
Hokkaido: Native iron has been reported from several Hokkaido localities. (Where??? = awaruite???)
Nagano: The so-called "native iron" grains from peridotite in Oshika-mura are actually native nickel or awaruite (qv).
Yamanashi: A magnetite-rich lava flow from Mt. Fuji contains native iron at Kawaguchiko on the far northern lower slopes, formed by reduction in contact with charcoal from burnt trees incorporated into the lava.
"ISHIGANEITE"
= mixture of cryptomelane (qv) and birnessite.
ISHIKAWAITE (ishikawa-seki)
Fukushima: The type locality for this rare, essentially uranium-iron-niobate, is the Ishikawa district, where it occurs as black, tabular metamict crystals to 1cm, with brilliant resinous to waxy luster, in pegmatite with samarskite-(Y), fergusonite, zircon, monazite-(Ce) and xenotime, and also in river sand and gravels derived from the pegmatite. Highly radioactive. The original 1922 analysis was (as wt% of oxides): Mg 1.07, Ca 0.86, Mn'' 0.40, Fe'' 11.78, Al 0.87, REE 8.40, U 21.88, Sn 1.20, Si 0.30, Ti 0.21, Nb 36.80, Ta 15.00, water 0.89. For many years there was much confusion as to whether this represented a new species or was just a uranium-rich variety of samarskite or "samarskite-Fe", but it is now confirmed as a species, the uranium-dominant member of the samarskite group, all of which contain essential Fe. The REE are mostly Y, part of the Fe'' has to really be Fe''' to balance the charges in the coupled substitution (UFe'',YFe'''), and the minor Mg, Al, Si is probably attributable to a small amount of vermiculite or chloritized biotite, which leaves us with the following empirical formula for ishikawaite: (U 0.466 Fe'' 0.516 Ca 0.044 Mn'' 0.016, Y 0.214 Fe''' 0.214)1.96 (Nb 1.59, Ta 0.390, Sn 0.046, Ti 0.016)2.04 O 8. The crystal shape is orthorhombic, with axial ratios a:b:c = 0.9451:1:1.1470, exhibiting faces c(001), a(100), g(210), h(320), m(110), n(140), b(010), r(144) and a(101). Since annealing this metamict material "restores" a monoclinic structure, ishikawaite has been interpreted as "monoclinic, pseudo-orthorhombic", but more likely the annealed structure is a synthetic distortion of the original truly orthorhombic crystal. (Streak blackish brown; conchoidal fracture; density 6.2 to 6.4; H 5-6.) The type specimen was allegedly destroyed in WWII. Also, not uncommon as pitch brown-black, rounded to roughly prismatic forms to 1cm at Shiozawa and Wagu in this district. (Much of the ishikawaite from the Shiozawa and Wagu areas has been previously mislabelled "samarskite".)
ISOCUBANITE (iso-kyuuba-koh)
Okinawa: In "black smokers" of the "Jade" seafloor hydrothermal field, Izena Cauldron, triangular to lozenge-shaped crystals from 0.03 to 0.1mm as abundant but unevenly distributed inclusions in sphalerite and sphalerite pseudomorphs after barite. Seen as sharp equilateral triangles in polished section. Alters to a mixture of chalcopyrite and pyrrhotite.
ISOFERROPLATINUM (iso-tetsu-hakkin)
Hokkaido: Teshio, and in the Uryu river, and in the Peichan river, and at Horokanai. Includes most of the material in japanese collections normally labelled just "PLATINUM" (qv).
ITOIGAWAITE (itoigawa-seki) (IMA # 98-034)
Niigata: The type locality for this rare strontium analogue of lawsonite is Oyashirazu in Itoigawa (whence the name), where it occurs as vitreous, transparent azure blue, short tabular crystals to 0.1mm, associated with interstitial natrolite and 1mm thick natrolite veinlets, embedded in lavender-colored titanian jadeite, as veinlets in jadeitite boulders and pebbles on the seashore. Rare larger masses, irregular aggregates to 1.5cm across appear dark blue. The color is due to Ti-Fe (as in sapphire). Colorless itoigawaite has also been found, and such material is very difficult to recognize. Occasional associates are zircon and rengeite. Of hydrothermal origin in late stage of jadeitite formation in the contact zone of a serpentinite breccia at the mouth of Himekawa river. Japanese collectors had long held itoigawaite in collections, labeled as "blue jade", without being aware that some of the blue jade contained a new mineral species. The mineral shows one good cleavage; no fluorescence under SW UV; hardness 5-5.5; brittle; white streak; density 3.37. Type material is quite pure, with little substitution of Ca for Sr.
IWAKIITE (iwaki-koh)
Fukushima: The type locality for this manganese-iron oxide (previously also known as "alpha-vredenbergite") is the Gozaisho manganese mine. The name derives from Iwaki Province, the feudal-era name of Fukushima Prefecture. It forms small, greenish black, bright metallic granular aggregates, strongly magnetic, in a braunite ore band in regionally metamorphosed bedded manganese ore body in chert. Associated with rhodonite, quartz, braunite, hematite, spessartine and minor rhodochrosite. May tarnish dark blue.
IWASHIROITE-(Y) (IMA# 2003-053) (iwashiro-seki)
Fukushima: This new monoclinic YTaO4 from Suishohyama is a dimorph of formanite, and the Ta-analogue of beta-fergusonite-(Y). Found in the autumn of 1999 as only one single crystal, almost 2cm across, with square cross-section, embedded in red feldspar in pegmatite. Dark reddish brown, amber brown to brown, somewhat translucent, vitreous to adamantine. Crystal is zoned, with metamict uranium-rich and crystalline U-poor zones, which enabled determination of the structure. Intense search has so far produced no further specimens, and so-called "iwashiroite" on the rare species market is generally metamict zircon or fergusonite; Caveat emptor! (The original specimen is at the National Science Museum.)
IZOKLAKEITE (izokurehku-koh)
Yamanashi: Acicular xls of bismuthian izoklakeite at the Otome mine. Cannot be visually distinguished from the giessenite and kobelite here. (Some or all of the "giessenite" from here is actually Bi-rich izoklakeite too.)
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