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Sadanagaite and Magnesio.Sadanagaite, New Silica-Poor Members of Calcic Amphibole from Japan

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Sadanagaite and Magnesio.Sadanagaite, New Silica-Poor Members of Calcic Amphibole from Japan American Mineralogist, Volume 69, pages 465471, 19E4 Sadanagaiteand magnesio.sadanagaite,new silica-poor membersof calcic amphibole from Japan Hrppnxo Sntrraezerr Geological Institute, Faculty of Science University of Tolcyo, Hongo, Tolcyo l13, Japan Mrcnrerr Buuxor Department of Mineralogy, The University Museum University of Tolcyo, Hongo, Tolcyo 113, Japan nxo Tonnu Ozewe Mineralogical Institute, Faculty of Science University of Tolcyo, Hongo, Tolcyo ll3, Japan Abstract Sadanagaite,(K,Na)CazGe2*,Mg,Al,Fe3*,Ti)r[(Si,AlhO22(OH)2] where Fe2* = Mg, Al = Fe3* and Si < 5.5, and its Mg-rich analogue,magnesio-sadanagaite Fe2+ < Mg, are extremely SiO2-poor new amphiboles, which require the compositional extension of the edenite-pargasiteseries, and amending of the classification and nomenclature of amphi- boles (Leake, 1978). Theseare monoclinic,C2, Cm or Cllm; a = 9.922(10),b : 1E.03(2),c : 5.352(9)4,B: 105.30(10f,Z = 2 for sadanagaitewith Si - 5.0, and a : 9.964(2),D : 18.008(3),c : 5.354(2)4,B = 105.55(2)",2= 2 for magnesio-sadanagaitewith Si:5.0. The strongest lines in the X-ray powder pattern for magnesio-sadanagaiteare: 8.48(80)(ll0), 3.39(40Xl3l), 3.28(100X240),3.15(70)(3r0), 2.951(50X22r),2.823(30)(330), 2.766(45)(33r), 2.707(60Xl5l),2.594(35X061),2.162(55)(261),1.654(30X461), thesebeing similar to thoseof X-ray powder patterns of SiO2-poorcalcic amphiboles, especially kaersutite. Both specieshave very similar physical properties, and are dark brown to black with a vitreousluster. Streak very light brown. Cleavage{110}, perfect. H (Mohs) : 6. Density (calc.) 3.30 g/cm3 for sadanagaite and 3.27 g/cm3 for magnesio-sadanagaite.Optically biaxial positive with2V = 80-X)" (meas.), 86" (calc.) for sadanagaite,and with2V close to 90o(meas,), 88'(calc.) for magnesio-sadanagaite.Refractive indices: a = 1.673(2),F = 1.684(2),y-1.697(2);c:Z=28'(sadanagaite),anda=1.674(2),8--1.686(2),y= 1.699(2);c:Z : 26" (magnesio-sadanagaite).Pleochroism strong with X' = pale brown to Z' - greenish brown (sadanagaite)and with X' = colorless to Z' = brownish yellow (magnesio-sadanagaite). The minerals are found in two separate localities, Yuge and Myojin Islands, Japan, where they occur in Al-, Ti- and Fe-rich skarns in recrystallized limestone beds, forming bands with vesuvianite, spinel-hercynite, sphene, ilmenite and apatite in the former locality, and forming small lenses with titaniferous fassaite, vesuvianite, spinel-hercynite, sphene,ilmenite, magnetite,apatite and perovskite in the latter. Among them the peculiar composition of titaniferous fassaite is discussed with special reference to its extremely SiO2-poor, Al2O3- and TiO2-rich composition. The names are for Professor Ryoichi Sadanaga,Mineralogical Institute, University of Tokyo, in recognition of his outstanding contributions to the fields of mineralogy and crystallography. I Presentaddress: Geological Department, Geological Survey ofJapan, Higashi l-l-3, Yatabe, Ibaraki 305, Japan. 0003-004)uE4l0506-965$02. 00 466 SHIMAZAKI ET AL,: SADANAGAITE AND MAGNESIO-SADANAGAITE Introduction brown seams intercalated with limestone in the quarry. The classification and nomenclature of amphiboles by Myojin Island, one of islands known as the Shisaka Leake (1978)defines no lower limit of Si content in calcic Islands, consists largely of somewhat gneissosegranitic amphiboles,although a prefix "subsilicic" is recom- rocks and gneisswith some limestonebeds. Sato (1926) mendedwhen the number of Si is less than 5.75 on the first reported the occurrenceofclinopyroxene from skarn basis of 23 oxygens. The occurrence of amphibole with lenses in one limestone bed, and subsequently Kuno Si : 5.27has beenreported by Appleyard (1975)and the (1960) described this as titaniferous pyroxene, and necessity of new end member NaCa2Mg3Al2Si5Al3 Miyahisa et al. (1980)as fassaite.The dark colored lenses O22(OH)2("Al-pargasite") has been suggested(Bunch in the limestone bed include locally amphibolesof parga- and Okrusch, 1973;Doolan, Zen and Bence, 1978). site to magnesio-sadanagaitecomposition in addition to This contribution provides natural examplesof amphi- the above clinopyroxene. boles with lower Si than the above composition from two separate localities, Yuge and Myojin Islands, Ehime Occurrence and associated minerals Prefecture, Japan. The composition of these amphiboles According to the geological map compiled for Ehime is so different from that of pargasite with regard to the Prefecture (1962),Yuge and Myojin Islands are situated number of Si that they are proposed as new Si-poor near the boundary between the Paleozoic-MesozoicChi- members(Si < 5.5) of the pargasite series. The minerals chibu Belt and the Ryoke Metamorphic Bett (Fig. l). and mineral names, sadanagaiteand magnesio-sadana- Yuge Island belongs to the former belt with the intrusion gaite, have been approvedby the Commissionon New of the Mesozoic Hiroshima-type granitic rocks. Myojin Minerals and Mineral Names, IMA (CommissionNos. Island belongsto the latter belt, and weakly gneissose 80-27and 82-102).The names are for Emeritus Professor granitic rocks are associatedwith high temperature-low Ryoichi Sadanaga,Mineralogical Institute, University of pressure-type metamorphic rocks. Both localities are Tokyo, in recognition of his outstanding contributions to only about 15 km from each other, and are thought to the field of mineralogy and crystallography. Type speci- have similar geologic environments, although they are mens have been deposited in the Department of Mineral- located in diferent geologic belts. No tectonic zone ogy, the University Museum, University of Tokyo, Ja- separatesthem, and the boundary between the belts is pan. basedonly on the metamorphic grade. Both Yuge and Myojin are small islands located in the In the Yuge limestone quarry, sadanagaite-bearing Seto Inland Sea, southwesternJapan (Fig. l). In Yuge skarn occurs as seamsin limestone with variable widths Island, where a limestonequarry has been operated,a up to a maximum of 50 cm. The skarn seamsusually have sadanagaite-bearingvesuvianite skarn occurs as dark a symmetrical structure, that is, they consist of a wollas- rrd t3s. o'+ + HONSHU ..i.,,,$ -------sS "t4 ll$'r'-- -t,' 5 '--.^*g gES O SOKM 0t€rss0€E OR ilIIE Fig. l. Location and simplified geology of the Yuge and Myojin Islands, Ehime Prefecture, Japan. SHIMAZAKI ET AL.: SADANAGAITE AND MAGNESIO-SADANAGAITE 467 tonite zone, a garnet-vesuvianite zone, and a vesuvian- ent of the skarn, in contrast with the Yuge occurrence. ite-sadanagaite zone, traversing from limestone to the The skarn includes, besides clinopyroxene, various center of the seam. Sadanagaitemay be lacking in the amounts of spinel, vesuvianite, magnesio-sadanagaiteto central vesuvianitezone of some seams.The sadanagaite- pargasite, phlogopite and minor amounts of sphene, il- bearing zone occurs as a compact, dark brown band, menite, magnetite, pyrrhotite, apatite and perovskite. consisting of vesuvianite and sadanagaitewith minor Both clinopyroxene and magnesio-sadanagaitefrom this amounts of spinel, sphene, ilmenite and apatite. Sadana- locality are short-prismatic to granular in shape with a gaite appears as isolated prismatic crystals with a maxi- maximum diameter of a few hundred microns. mum length of I mm or as polycrystalline aggregatesin The composition of the clinopyroxene has been debat- matrix vesuvianite. The composition of sadanagaitesis ed since the first description by Sato (1926).Kuno (1960) quite variable with respect to SiO2as will be describedin showed that the clinopyroxene is rich in AlzOr (6.89 the following section and shown in Table l. wt.Vo) and TiOz Q.47%) by wet chemical analysis. Preliminary electron microprobe analyses show that Miyahisa et al. (1980)concluded that it is fassaitewith up the vesuvianite is rich in titanium with TiO2 contents of 5 to 5 wt.%oAl2O3 using the electron probe microanalyzer. wt.Vo or more. The spinel is hercynite with variable Most of the skarn lenses contain clinopyroxenes with amountsof the spinel molecule. Amounts of up to 5 wt.Vo compositions similar to those given by Kuno (1960)and Al2O3 are present in the sphene. Ilmenite has a small Miyahisa et al. (1980). The associated amphiboles are amount of the geikielite molecule. (ferroan) pargasite to less commonly magnesio-hasting- In Myojin Island, the magnesio-sadanagaite-bearing site. skarn occurs as a lens or as an irregularly shapednodule The bulk chemical compositions of the lensesare quite in crystalline limestone. Some lenses show a structure variable, and in some rare lensesthe compositionsof the similar to that of boudinage.The size of the lens or nodule clinopyroxene and amphibole become very Si-poor, and although variable rangesup to several tens of centimeters Al- and Ti-rich. Magnesio-sadanagaitegiven in Table l, in width. The occurrenceofthe skarn is reported in detail No. 4, is an example from an extremely Si-poor lens. The as a fassaite-spinelrock by Miyahisa et al. (19E0). As associatedclinopyroxene is also unusually Si-poor, with noted in their paper, clinopyroxene is the main constitu- the number of Si : 1.3 on the basis of 6 oxvsens. An Table l. Electron microprobe analysesof sadanagaitesfrom the Yuge (Y) and Myojin (M) skarns No. r (Y) 4 0,r) s (Y) sio2 30.2 29.9 3I. I 32.L 33.5 29.5 Tio2 4.0 4.3 4.5 3.2 2.L 4.0 A1203 24.8 22.6 22.5 22.0 L9.7 23.2 FeOr L5.2 L7.4 L6.2 L3.7 17.8 15.4 MnO 0.1 0.3 0.4 0.1 0.5 0.3 Mgo 6.6 6.1 6-6 8.0 6.4 CaO L2.3 1r.9 L2,0 L2.5 11.9 1r. 9 Na2O r. u 0,6 0.6 o.7 L.2 K2o 3.7 3.7 3.6 3.8 3.r 3.5 Total 97.9 95.8 t I .5 96.1 96.2 97.2 Nrmbers of cations on the basis of 23 oxygens si 4.6il n.eo) q.ttl 4.e5) s.zl'l l.szl lrrV ,.rrj8'00 ..rnJt'oo ,.rrJt.oo ,.orjt.oo z.tale-oo 3.4sJ8-oo -, vr Ti -J+ !e Fe2+ Mn M9 Ca 2.01 2.0r 1.99 r.99 I.97 L-97 2.07 2.07 2.00 2.00 1.96 1.96 Na 0.2e1_ -_ o.r7l o.tel o.zzl o.gzl o.2o'l K o.t.Jt'oo o.toJo'tt o.rrJo'tt o.rulo't' o.rrJo''e o..rlo'tt *Total iron.
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