著者

丸山 茂徳 植田 良夫

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.70, no.2, pp.47-52, 1975-02-05 (Released:2008-08-07)

参考文献数

26

被引用文献数

8 14

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Xenoliths in the Kitomyo ultrabasic body (NS-2.5km, EW-4.5km in width) in Kizawa village, Tokushima Prefecture, are composed of mainly amphibolites, psammitic and basic schists with albite spot, quartzose schists, greenstones and sedimentary rocks, the latter two being derived from country rocks. The mode of occurrence, petrographic features and chemical analyses of garnet, chlorite and amphiboles of the metamorphic rocks are described. Petrographically, the low grade schist xenoliths are quite similar to basic and psammitic schist of the Sanbagawa metamorphic belt, and they are distinct from the Terano metamorphic rocks. But the K-Ar ages of muscovites in psammitic and quartzose schist with albite spot are 402 m. y. and 405 m. y. respectively. The significance of the presence of Sanbagawa-type schists in the ultrabasic body of the Kurosegawa tectonic zone is briefly discussed.

著者

大町 北一郎 鈴木 淑夫 早川 彰

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.39, no.4, pp.154-166, 1955-08-01 (Released:2008-03-18)

参考文献数

5

被引用文献数

2 1

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The field investigations of the iron beach sand deposits along the coast of the Pacific ocean from Mukawa to Horobetsu were carried out in the autumn of 1954. The iron placers occur along many shores and often produce by concentration from an elavated beach. More or less of the iron sands are seen all along many shores of the coast in the district, but the comparatively rich layers have only limited development being restricted mainly to the vicinities of Mukawa, Tomakomai, Shiraoi, Ponayoro, Noboribetsu and Horobetsu in where the last one is noteworthy and is now mined. In general the thickness of iron sand rich layers varies from 5 to 30cm, though that of the layer at Horobetsu reaches 50cm. The size of the magnetite grains is about 0.03mm in average, and the general contents of Fe and TiO2 in the iron sands are 25-45% and 2-5% respectively. The mineral and rock grains associated with the magnetite sand are hypersthene, augite, olivine, hornblende, plagioclase, biotite, quartz, garnet, ilmenite, chromite, andesite, hornfels, radioralian chert, etc. The parent source of these sand garins is probably in the adjacent volcanic rocks though some of them may be ordinarily derived from the older rock series in the Hidaka district.

著者

Yu KODAMA Naotaka TOMIOKA Motoo ITO Naoya IMAE

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.115, no.5, pp.407-415, 2020 (Released:2020-11-03)

参考文献数

28

被引用文献数

4

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A focused ion beam (FIB) scanning electron microscope (SEM) equipped with a low–energy Ar–ion gun, an electron back–scattered diffraction (EBSD) detector, and an energy dispersive spectrometer (EDS) was newly developed for microfabrication, followed by submicroscopic chemical and crystallographic analyses in an identical sample chamber. The surface condition of mineral samples requires extreme care during FIB milling process, especially for EBSD measurement, as the EBSD pattern is greatly affected by a damaged amorphous surface caused by a high–energy Ga–ion beam (30 keV), even when this damaged layer is only tens of nanometers in thickness. Low–energy broad Ar–ion beam milling (1 keV) overcomes this problem and allows us to obtain sharp EBSD patterns. We applied the microfabrication–analysis protocol to a cosmic spherule. Comprehensive mineralogical datasets from SEM images, X–ray elemental maps, and EBSD patterns were successfully obtained from a minute mineral sample, where conventional cutting and polishing processes are not possible.

著者

Mitsumasa ETO Shunsuke ENDO

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.200127, (Released:2020-10-03)

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The Suo metamorphic complex in the Chugoku Mountains of southwest (SW) Japan represents Jurassic high pressure (P )/temperature (T ) type metamorphic rocks. Its high–grade part is exposed in the Nichinan area, where barroisite–bearing mafic schist occurs as ~ 50–m thick layers in pelitic schist. These mafic layers contain the common matrix assemblage barroisite + epidote + albite + quartz + titanite + phengite. Relic minerals (garnet, glaucophane, aegirine–augite, Si–rich phengite and rutile) of early–stage parageneses are preserved within albite porphyroblasts. The textural relations combined with pseudosection modeling suggest a clockwise P –T trajectory from epidote–blueschist facies through the garnet + clinopyroxene stable conditions to epidote–amphibolite facies. Two distinct phases of high–strain ductile deformation (D1 and D2) can be recognized in the area, and they are related to early and late stages of exhumation. Albite porphyroblasts initially grew statically between D1 and D2 at ~ 520–530 °C and ~ 0.8 GPa, and further retrogressive growth of albite rims and chlorite at the expense of barroisite is synchronous with D2. The lithological association, deformation structures and metamorphic conditions of the Jurassic Suo metamorphic complex are very similar to those of the Cretaceous Sanbagawa metamorphic complex, suggesting they have comparable exhumation processes as coherent–type high–P/T metamorphic complexes.

著者

Daisuke NISHIO–HAMANE Masayuki OHNISHI Norimasa SHIMOBAYASHI Koichi MOMMA Ritsuro MIYAWAKI Sachio INABA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.115, no.3, pp.286-295, 2020 (Released:2020-06-24)

参考文献数

30

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Petersite–(La) is a new mineral of the petersite series in the mixite group with an ideal formula of Cu6La(PO4)3(OH)6·3H2O from Ohgurusu, Kiwa–cho, Kumano City, Mie Prefecture, Japan. The mixite–group minerals occur in small cavities coated by chrysocolla developed along quartz veins. Four members from different cavities have been identified: petersite–(La), petersite–(Ce), petersite–(Y), and agardite–(La). Petersite–(La) occurs as a radial aggregate formed by acicular to hexagonal columnar crystals of yellowish green color. Crystals are elongated along [001] and the prismatic face is probably formed by {001} and {100} or {110}. It is non–fluorescent in UV light. Crystals are brittle, cleavage and parting are non–observed, and fracture is uneven. These characteristics are common in other mixite–group minerals. The calculated density of petersite–(La) is 3.33 g/cm3, based on the empirical formula and powder XRD data. It is optically uniaxial positive with ω = 1.680(3) and ε = 1.767(3) (white light), and pleochroism varies from light green to yellowish green. Based on the WDS analysis, the empirical formula of petersite–(La) calculated on the basis of P + As + Si = 3 is (Cu5.692Fe0.010)Σ5.702[(La0.148Ce0.122Nd0.117Y0.086Sm0.022)Σ0.495Ca0.372]Σ0.866(P1.890As0.799Si0.311)Σ3O10.320(OH)7.680·3H2O. Petersite–(La) is hexagonal (P63/m) with a = 13.367(2) Å, c = 5.872(2) Å, and V = 908.7(4) Å3 (Z = 2). The eight strongest lines of petersite–(La) in the powder XRD pattern [d in Å(I/I0)(hkl )] are 11.578(100)(100), 4.377(28)(210 + 120), 3.509(18)(211 + 121), 3.211(10)(310 + 130), 2.898(14)(221, 400), 2.656(10)(320 + 230), 2.526(11)(410 + 140), and 2.438(25)(212 + 122). Petersite–(La) is the third defined member in the petersite series and corresponds to the La–dominant analogue of petersite–(Y) and petersite–(Ce).

著者

井ノ上 幸造

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.83, no.1, pp.26-41, 1988-01-05 (Released:2008-03-18)

参考文献数

29

被引用文献数

11 10

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Takachiho composite volcano, located in south Ky ?? sh ??, Japan, is one of major members of the Kirishima volcano group. The composite volcano consists of four volcanic edifices which are partly overlapping and aligned in E-W direction. On the basis of field geology and tephrochronology, its growth-history can be divided into four stages. During the first stage, a conical stratovolcano, Futagoishi, was formed in the eastern end of the composite volcano. It is com-posed of an alternation of pyroclastic beds and lava flows. The activity of Futagoishi ended before the eruption of Ito pyroclastic flow deposit (22, 000 yBP) from the Aira caldera. The second stage activity started about 10, 000 years ago, after a repose of more than 12, 000 years. It was characterized by vulcanian eruption which continued semi-persistently through a long period of time, probably more than a thousand years. During this period a stratovolcano, Old-Takachiho, was built up on the western flank of Futagoishi, and a large amount of volcanic ash accumulated concentrically around the volcano. The third stage activity was characterized by the eruption of several thin lava flows and scoria from the vent close to Old-Takachiho Volcano. This activity resulted in formation of a small conical stratovolcano, Takachiho-no-mine, on the western slope of Old-Takachiho. At the end of this stage, enormous lava flows were successively effused from the top crater and flowed downward widely. Later lava flows, however, did not reached the foot of the slope due to decrease in effusion rate and piled up around the crater, resulting in the construction of an exogeneous lava dome on the summit. After several hundred years of quiescence, the present stage activity began about 2, 500 years ago. This activity was characterized by sub-plinian eruptions which occurred intermittently and produced thick scoria and ash beds on the eastern foot of the composite vlocano. By repeated eruptions of a great volume of scoria and lava flows, a new vlocano, Ohachi, was born on the western flank of Takachiho-no-mine volcano, and has been active since then. The growth-history of Takachiho composite volcano revealed the following two features: 1) the volcanic activity may have been controlled by the underlying E-W fracture, as suggested by the shifting of the vent position from east to west, and 2) the styles of explosive activity of the composite volcano have gradually changed with time from vulcanian eruption to sub-plinian one.

著者

松原 聰

出版者

Japan Association of Mineralogical Sciences

雑誌

日本鉱物学会年会講演要旨集

巻号頁・発行日

pp.25, 2002 (Released:2003-04-18)

著者

Kota SUZUKI Tetsuo KAWAKAMI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.114, no.6, pp.267-279, 2019 (Released:2020-01-22)

参考文献数

32

被引用文献数

12

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The metamorphic pressure–temperature (P–T) conditions of high–grade pelitic gneisses from Akarui Point, Skarvsnes, Skallen, and Rundvågshetta in the Lützow–Holm Complex (LHC), East Antarctica are re–examined by applying the Zr–in–rutile geothermometer to rutile inclusions in garnet enclosing Al2SiO5 minerals and to matrix rutile grains. By utilizing the P zoning of garnet to indicate isochronous surface, samples from Akarui Point, Skarvsnes, and Skallen were shown to have experienced almost the same P–T conditions around the kyanite/sillimanite transition boundary (~ 830–850 °C/~ 11 kbar). From Rundvågshetta, higher–T condition (850 ± 15 °C/0.1 kbar to 927 ± 16 °C/12.5 kbar) was confirmed from rutile inclusions in garnet enclosing sillimanite. Matrix rutile yielded similar temperature as inclusion rutile for Akarui Point, Skarvsnes, and Skallen samples. Therefore, the traditional metamorphic zone mapping based on matrix mineral assemblages, which classified Akarui Point as belonging to the transitional zone between the upper–amphibolite and the granulite facies zones, does not reflect the highest metamorphic conditions attained. The P–T–t evolution of the LHC needs to be re–evaluated utilizing detailed petrochronological approaches.

著者

西山 忠男 宮崎 一博 伊東 和彦 佐藤 博樹 金澤 英樹 玉田 攻 北澤 恒男 小池 正義

出版者

Japan Association of Mineralogical Sciences

雑誌

日本鉱物学会年会講演要旨集

巻号頁・発行日

pp.47, 2004 (Released:2005-03-10)

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Ito et al.(2003)において合成されたカンラン石単結晶中に見られる波動累帯構造の詳細を報告し,成因を考察する.これまで2成分系において成長速度の濃度依存性を組み込んだ拡散境界層モデルが提唱されているが,われわれの場合組成変動幅が小さいので問題にならず,既存のモデルでは説明不可能である.ここではメルト中の拡散が2成分系ではなく3成分系で起こると考え,FeOとMgOの拡散係数の大きさが有意に異なる場合はSiO2のアップヒル拡散が生じることを示す.カンラン石の成長によりこのようなアップヒル拡散が生じると,拡散境界層におけるメルト組成は,カンラン石のバルク組成から外れることになり,それにより成長が阻害される.SiO2の濃度勾配が解消され,拡散境界層のバルク組成が再びカンラン石のそれに近くなると成長が再開する.このようなフィードバック機構により波動累帯構造が形成されると考えられる.

著者

沼子 千弥 山口 力也 箕村 知子 小藤 吉郎

出版者

Japan Association of Mineralogical Sciences

雑誌

日本鉱物学会年会講演要旨集

巻号頁・発行日

pp.107, 2003 (Released:2004-07-26)

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軟体動物の貝殻には、構成する炭酸カルシウム結晶の形態により、稜柱構造(prismatic structure)、交差板構造(crossed lamellar structure)、葉状構造(foliated structure)、真珠構造(nacreous structure)などのように分類される殻体構造(shell structure)が存在する。また、炭酸カルシウムにはカルサイト、アラゴナイトのように様々な多形が存在するが、その存在比は非生物系と生物系で大きく異なっていることが、いわゆる生体鉱物におけるカルサイトーアラゴナイト問題として知られている。生物が鉱物種、結晶形態、殻体の中での分布の全てを制御しながら生体鉱物として炭酸カルシウム結晶を形成してゆくメカニズムには新規材料開発を考える上で模倣すべき点を多く含まれると考えられ興味深い。そこで本研究ではそのメカニズム解明の第一歩として、現生の軟体動物数種について実際にそれらの生物が持っている殻体構造の軟体動物の種類による存在量や分布違い、そして殻を構成する炭酸カルシウム鉱物の種類とその量比について記載を行った。 軟体動物はクロアワビ、マガキなど日本近海で採集可能なものを海水棲・淡水棲、二枚貝類・腹足類・多板綱などを網羅するようにおよそ10種類選択し、軟体部と貝殻を分離した。貝殻は風乾・粉砕後、光学顕微鏡下で殻体構造の異なるものを分類し、それぞれ走査型電子顕微鏡で観察を行った。さらに粉末X線回折計を用いて貝殻を構成する鉱物種の同定と量比の算出を試みた。またいくつかの試料について、単色ラウエ法やプリセッション写真法により、結晶の方位や状態についてさらに詳細な検討を加えた。 実験の結果、軟体動物の種類が異なると、同じ殻体構造を持っていても構成する鉱物種の種類と量に差があり、殻体構造の結晶の形状の決定要因は構成鉱物種の結晶の自形のみではないことが明らかとなった。また同一殻体構造に複数の鉱物種が存在する場合でも、異方性や結晶粒の大きさなどにも鉱物種ごとに差違が生じていることが分かった。今後より多くの種類の生物について硬組織の構造と構成鉱物種の関連を調べてゆく必要があると考えられた。

著者

舟山 裕士 阿部 宏

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.58, no.4, pp.121-135, 1967-10-05 (Released:2008-08-07)

参考文献数

12

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The mineral deposits of the Oppu mine, Aomori Prefecture, consist of epithermal fissure-filling chalcopyrite-sphalerite-galena veins in the Neogene sediments. On the basis of lithology and characteristics of sedimentation, stratigraphy of the Oppu mining districts is divided into the following formations: Quaternary Terrace deposits and Talus deposits Oppudake formation Tertiary Miocene Oppu formation Maenosawa formation Koyunosawa formation Yunosawa formation Pre-Tertiary Basement complex The country rocks of the mineral deposits are Oppu formation (andesitic-dacitic lapilli tuff, coarse tuff and siltstone) and Oppudake formation (salic pumiceous tuff). The geological structures are characterized by large domes which are sometimes accompanied with faults and foldings. Faults are common in the area studied and can be classified into the following four major systems-NE-SW system, WNW-ESE system, ENE-WSW system and N-S system. The distribution of mineral deposits and ore shoots have close relations with the some geological structures. For instance, main mineral deposits are located usually in the combination zone of normal and low dipping reverse faults in this mining area. Especially, the veins are controlled by the sedimentary structures and thrust faults (Figure 5). These structural conditions which control the ore shoots have been stressed in this paper.

著者

鳥海 淳 三河内 岳 宮本 正道

出版者

Japan Association of Mineralogical Sciences

雑誌

日本鉱物学会年会講演要旨集

巻号頁・発行日

pp.146, 2003 (Released:2004-07-26)

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サハラ砂漠では近年大量の隕石が発見されているが、その中には火星隕石や月隕石といった珍しい種類の隕石が比較的多く含まれているのが特徴である。本研究では、このような最近新しく見つかった隕石の1つで、外観的特徴から月隕石の可能性があるものを分析・分類した。さらに、その鉱物学的・岩石学的特徴から、この隕石の起源、および他の隕石との関係について考察を行った。 この隕石はミリメートルサイズの岩片とそれよりやや小さい鉱物破片が黒灰色の石基に埋まっている角レキ化した組織を示し、主要構成鉱物は斜長石、輝石、カンラン石である。岩片には、いくつかの種類のものが見られるが、特徴的なものとしては、オフィティックな玄武岩質のものやインターサータルな組織を示すもの(インパクトメルト)が含まれる。輝石の組成は、非常に幅広く、En81Fs16Wo3からEn2Fs78Wo20を経由して、En34Fs34Wo32に及んでいる。特に、オフィティックな玄武岩質の岩片中に見られる輝石は著しい化学的ゾーニングを示している。輝石のFe/Mn(重量%比)は、60から70である。カンラン石の組成は、Fa14からFa61の範囲であるが、大部分のものは、Fa16-40である。斜長石は、An成分に富んでおり、An91からAn98となっている。他に少量であるが、アパタイト、シリカ、鉄ニッケルのメタルなども含まれている。また、その他の鉱物学的特徴としては、輝石中に幅最大数マイクロメートルの離溶ラメラが観察された。 以上の鉱物学的・岩石学的研究の結果(特に輝石のFe/Mn比より)、この隕石は月起源だと考えられ、しかも月の高地の部分の物質と海の部分の物質の両方を含んでいることが分かった。分類としては、月起源角レキ岩である。また、他の月隕石との比較の結果によると、この隕石はYamato793274/981031、EET87521/96008、QUE94281と最もよく似ており、同じ月の部分からきた可能性がある。しかし、これらは、いずれも南極隕石であり、この隕石と地球への落下がペアとは考えられない。また、その他のサハラ砂漠産の月隕石に、この隕石とペアととなるものもこれまで見つかっていない。この隕石はまだ正式名が付いていないために、現在その作業を進めているところである。

著者

川上 紳一 金折 裕司 大野 照文

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.87, no.10, pp.393-411, 1992-10-05 (Released:2008-03-18)

参考文献数

127

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Soon after the formation of the Earth by collisional accretion of planetesimals in the primordial solar nebular, its interior has been differentiated gravitationally to form the central metallic core, silicate mantle and crust, atmosphere and ocean. The sequence of differentiation was very rapid during the formation and subsequent early history, since the interior has been maintained hot by the heating of accretional energy, gravitational energy of core-mantle separation and energy released by the radioactive neclides. The differentiation and interactions between the core, mantle, crust, atmosphere and ocean has been continued throughout the Earth's history less effectively but still a significant way. The mode of interactions between the subsystems of the Earth includes mass transfer (geochemical cycle), electromagnetic interaction, and mechanical interactions such as angular momentum exchange, tidal interaction and convective flows and plate motions. Since these interactions have been maintained by the energy of radioactive nuclides and solar energy, the Earth system can be regarded as disequilibrium dissipated system with highly non-linear behavior. Many rhythmical variations in the Earth environments such as climate change, sea level change, geomagnetic variation, plate velocities and orogeny, volcanic and seismic activities are expected to show signatures of the non-linear dissipative systems. Specifically we expect the period bifurcation phenomena revealed in many non-linear systems would exist in the rhythmical variations in the Earth's history. Here we reviewed the spectrum structures of galactic motions, solar activities, orbital motions of the Earth and planets with special reference to the Milankovitch cycles, the Earth rotatonal variation, geomagnetic variations, variations in the atmosphere and ocean phenomena, climate change, meteoroid impact and mass extinciton episodes, and then revealed nature of multi-sphere interactions in the Earth's history in the frequency domain. Some future problem to explore the nature and mechanisms in the multi-sphere interaction and evolution of the Earth were discussed.

著者

Takahiko OGAWARA Junji AKAI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.131125a, (Released:2014-05-16)

被引用文献数

4 5

著者

Osamu IKEDA Tatsuya SAKAMAKI Tomonori OHASHI Masahisa GOTO Yuji HIGO Akio SUZUKI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.181115b, (Released:2019-06-06)

被引用文献数

9

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The sound velocity and density of ε–FeOOH have been simultaneously measured up to 24 GPa at room temperature using an ultrasonic pulse–echo–overlap method and a Kawai–type multi–anvil apparatus at BL04B1 in SPring–8. In the experimental pressure range, the velocity of both the P– and S–waves of ε–FeOOH was ~ 15% lower than that of an isostructural phase δ–AlOOH. The pressure dependence of the determined adiabatic bulk modulus (KS) increased in the higher pressure range beyond 17 GPa, whereas that of the axial ratios a/c and b/c did not transition from negative to positive. A similar change of pressure dependence of KS was observed in δ–AlOOH, which is followed by a transition of proton distribution state to disordered, but the axial ratios of ε–FeOOH indicate that the transition would not occur up to 24 GPa.

著者

山田 隆 滝沢 実 丹下 一夫

出版者

Japan Association of Mineralogical Sciences

雑誌

日本鉱物学会年会講演要旨集

巻号頁・発行日

pp.123, 2003 (Released:2004-07-26)

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埼玉県秩父市浦山の旧マンガン鉱山から本邦で初めて確認されたメタスウィッツァー石(metaswitzerite)について、その鉱物学的性質と共出鉱物に関し報告する。 メタスウィッツァー石;(Mn,Fe)3(PO4)2・4H2Oは1967年に初めてスウィッツァー石(switzerite)として記載されたが、その後の研究で7水和物;Mn3(PO4)2・7H2Oの脱水したものと確認されたため、1986年に7水和物をswitzerite、4水和物をmetaswitzeriteと再定義された。いずれも、North Carolina州、Kings Mountain近郊のFoote Mineral Company spodumene mineの石英-長石-リチア輝石ペグマタイトの割れ目より産した。スウィッツァー石は短時間で不可逆的に脱水しメタスウィッツァー石に変化するため新鮮な標本はまれである。鉱物名は、スミソニアン博物館の鉱物科学部門の名誉部長であるGeorge Switzer博士にちなんでswitzeriteが、その変化型としてmetaswitzeriteが名付けられた。 浦山の変成層状マンガン鉱床から産するメタスウィッツアァー石は、菱マンガン鉱やばら輝石からなる低品位のマンガン鉱石の割れ目に、長さ数ミリ以下のガラス光沢白色半透明の長板状結晶あるいは絹糸光沢半透明針状結晶として産する。いずれも若干の黄色から桃色味を呈する。劈開は板の方向に完全で脆く、硬度は2以下である。 化学組成は、Mn,Fe,Pを主成分としZnやAsは含まない。 X線粉末回折(XRD)パターンd(Å),(相対強度):8.54(100), 7.14(34), 6.77(29), 6.38(21), 5.01(16), 4.87(22), 4.25(26), 3.63(13), 3.15(10), 2.84(12), 2.77(12), 2.13(14), 2.11 (12) となり原産地のデータとよい一致を示す。 本鉱物は、母岩の割れ目から空気中にさらされた後一定時間が経過しており、もともとスウィッツァー石であった可能性も否定できない。新たな新鮮な標本の獲得がまたれる。

著者

田窪 宏

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.75, no.9, pp.300-312, 1980-09-05 (Released:2008-08-07)

参考文献数

30

被引用文献数

1 1

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Experiments on the crystal growth of materials belonging to the A12O3-TiO2 system and on the high-temperature behaviour of natural star-sapphire were made with special reference to the genesis of regular arrangement of the ruitle needle crystals in and on corundum crystals. The crystals were grown by using direct fusion, flux-fusion and hydrothermal methods under the various conditions of temperature, chemical concentration, cooling mode, temperature gradient and oxygen partial pressure. The following results were obtained: (1) When a thin layer of melt made from TiO2 powder or from mixture of Al2O3 and TiO2 powder was slowly cooled on (0001) face of corundum substrate, the regular arrangement of acicular rutile crystals was easily formed on the substrate. (2) The βAl2TiO5 crystals grown from the melt on the substrate did not show the regular arrangement. (3) When crystals of corundum and rutile were synchronously grown by the monotonous slow-cooling of flux-melt in air, no regular intergrowth appeared in both as-grown and aged corundum crystals. (4) When the intermitent flucutation of temperature was introduced during the slow-cooling in the above method, the conspicuous zonal structure composed of various imperfections appeared in the as-grown corundum crystals. After aging in air, the regular arrangement of rutile appeared on the (0001) faces and along the imperfection zones of corundum crystals. (5) When rutile was crystallized synchronously with corundum or epitaxially on the (0001) face of corundum from flux-melt in oxygen gas flow or from hydrothermal solution, no regular intergrowth was formed. (6) In the presence of flux-melt, the regular arrangement of rutile on the corundum substrate was promoted in air or in reducing atmosphere. (7) Epitaxial growth of corundum on a rutile single crystal did not occur in any of the growth methods mentioned above. (8) When natural star-sapphires were heated above 1200°C, the regular arrangement of rutile needles fell into disorder from surface to inside and finally disappeared with leaving small gas-bubbles. Ti-atoms tended to migrate predominantly towards the surface and into the small cracks where rutile was recrystallized. Based on these results and those reported by other authors, critical examinations were made as to such problems as solubility of Ti into corundum, stability of βAl2TiO3, removal of Ti from corundum technology for synthesis, mechanical behaviour, epitaxis and natural occurrence. As a result of examinations, it seems that the “precipitation from solidsolution” theory, which is generally accepted as to the genesis of regular intergrowth in star-sapphire, is less plausible. Following two theories were developed on the genesis ofstar-sapphire. (1) Secondary and epitaxial crystallization of rutile along open spaces and imperfection-zones such as shear planes, tension cracks, zonal structure and inclusions, most of which are parallel to (0001) face. TiO2-component is supplied not only from the external sources, but also from the internal sources such as the imperfection-zones with higher Ti-concentration. (2) Synchronous and parallel growth of corundum and dendritic rutile crystals, being followed by survival of the twig crystals which preserve proper orientation for epitaxis.

著者

都城 秋穂

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.55, no.4, pp.179-184, 1966-04-05 (Released:2008-08-07)

被引用文献数

1 1

著者

谷口 広充

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.67, no.4, pp.128-138, 1972-04-05 (Released:2008-08-07)

参考文献数

22

被引用文献数

2 3

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Towada volcano, which is located in the northeastern part of Honshu, is a typical double caldera of Krakatau type, about 10km in diameter and 500m deep. It is formed on the basement composed of the Tertiary rocks and the Pleistocene volcanic rocks. The volcanic activity of Towada volcano can be divided into two stages by the formation of calderas. At the first stage, the activity is represented by mafic to intermediate andesite. Then, this activity was followed by the eruption of the tremendous amounts of dacitic ash falls and pumice flows. Following this the outer caldera was formed by the collapse of the upper part of the stratovolcanic cone. At the second stage, the activity, which is much smaller than the first cone, is also represented by mafic to intermediate andesite. After this activity much andesitic pumice fall erupted in the Holocene age, resulting in a smaller caldera, called “Nakanoumi”. The rocks of each stage are divided into two rock series, namely pigeonitic rock series and hypersthenic rock series. The earlier eruption is pigeonitic series and the later is hypersthenic. In the first stage activity, the change from pigeonitic series to hypersthenic series is continuous by petrographicaly. A magma of hypersthenic series would be produced by a magma of pigeonitic series by fractional crystallization under higher oxygen partial pressure and lower temperature conditions.

著者

Mutsuko INUI Ayato TANIFUJI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.113, no.4, pp.181-189, 2018 (Released:2018-09-09)

参考文献数

24

被引用文献数

3

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Traditional metamorphic geology admitted that the appearance of specific index mineral, such as garnet, indicated the rocks experienced higher peak metamorphic condition. It is largely true, but it is still unclear what is going on in the rocks at the very start of the garnet formation. One of the key must lie in the area where apparent isograd is outcropped. Nagatoro area is located in the Kanto Mountains, and it is where the low grade metamorphic rocks of the Sanbagawa metamorphic belt are exposed. Appearance of garnet is the index of the higher metamorphic grade in this area. Several outcrops in Nagatoro area are known to contain garnet, thus being good samples of the outcropped isograd. In this study, spatial distribution of garnet within such an outcrop several tens of meters long was investigated. The samples are pelitic schists, and the mineral assemblage was basically quartz, plagioclase, muscovite, and chlorite. 36 of the 55 samples contained garnet. Garnet grains were small, most of them with diameters less than 100 µm. Most of the garnet grains were euhedral to subhedral and were found within micaceous lamellae which form the foliations of the pelitic metamorphic rocks. The micaceous lamellae were constituted mainly by muscovite with lesser amount of chlorite. Occurrence of garnet–bearing rocks within the outcrop seemed to be restricted in certain structural layers. The structural layers are known to be nearly parallel to the lithologic boundary in this area. Mapped chemical profiles of garnet revealed that the garnet grains exhibited euhedral growth of the crystal. The core part was relatively large and homogeneous, with quite a high Mn end–member (spessartine) content (XSps > 50%). Irregular shaped inner core was preserved. These features indicate that the texture preserves the beginning stage of garnet growth. The trend of chemical composition of garnet rim and adjacent chlorite is consistent with the bulk rock chemistry control. Spatial distribution of garnet, at the start of its growth, was probably controlled by the bulk rock chemistry.