The examined is anorthoclase cryptoperthite (Or₄₀, Ab₅₀, An₁₀) having a bluish purple iridescence which may be caused by fine lamellae in parallel to rhombic section (near (^-601)). The is composed of one monoclinic potassium phase, one monoclinic sodium phase and three triclinic sodium phases, all these four sodium phases having same chemical composition. The iridescence disappeared on heating the at temperatures above 618°C at which the lost the lamellar structure.
In the light of the mutual orientation of those constituent five phases, the perthitic structure of the is a new type, a model of which is proposed in Fig. 7.

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Since 1921, Kozu, Endo, Hadding, Ito, and Chao and Taylor had investigated into the interlamination of constituent feldspars of by X-ray methods. It seems however that the problem of the modes of interlamination still defies satisfactory solution. The writers have discovered that moonstones from granitic pegmatites in Shiga Prefecture, Japan, have a new type of inter-lamination of four constituent feldspars. Of these feldspars, one is monoclinic potassium-rich and the remaining three triclinic sodium-rich, two of which are twinned after the albite law. All the (010) planes of the four constituent feldspars are parallel and all the c-axes of the three sodium-rich feldspars are identical in length, parallel in direction, and make an angle of 32′ to the c-axis of the potassium-rich one towards the a-axis of the latter.
This result shows that the interlamination of moonstones does not belong to one limited type, but is classified into such types as discovered by Ito, Taylor and the present writers.

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Orthoclase cryptoperthites containing the albite component approximately at 35-50 percent are not homogenized below the liquidus but they obviously become homogeneous only after being transformed into the high-temperature form which is stable from about 820°C up to nearly the melting point. Our experiments show that the transformation may be reversible. Presumably, all orthoclase cryptoperthites, in spite of their compositions, show the same behavior mentioned above when heated. A suggestion of the possible mechanism of the transformation and a model of the perthitic structure of orthoclase cryptoperthite are given.

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The from Haumyan, North Korea, which belongs to sanidineanorthoclase cryptoperthite series (after Tuttle, 1952), was observed in the transmission electron microscope, and it was found that the angle σ, which defines the position of composition plane (in the pericline twin), of the pericline twinned Na-phase of the is minus 4.5 degrees, and that the value of the angle σ is nearly the same as that of an anorthoclase twinned after the pericline law.
This fact can be used to estimate the degree of Al, Si order in the crystal structure of the cryptoperthite having Na-phase twinned after the pericline law.
And it is proposed that, at the temperatures between the liquidus and solvus curves in the phase diagram of the alkali feldspar, anorthoclase may be twinned after the pericline law, that is, the exsolution may be preceded by the twinning in the formation process of anorthoclase.

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High quality kaolin is mined at Meetiyagoda in southwestern Sri Lanka. The deposit occurs in a swampy area within the low-lying coastal region having a tropical wet climate. The kaolin clay beds form part of the Cenozoic fluvial sediments overlying the granulite and pegmatite of the Highland Complex formed by the late Neoproterozoic-Cambrian orogeny. The sedimentary clays are composed mainly of kaolinite and quartz. X-ray powder diffraction and scanning electron microscopy have revealed that kaolinite is well-crystallized variety and the platy crystals are not broken in the sedimentary clay. The sedimentary kaolin is considered to have been formed by intense tropical weathering of the aluminous granulite and pegmatite, and subsequently transported and deposited into low-lying swamps or marshes near the weathering crust over the basement rock. The kaolinite crystals might have undergone partial recrystallization in the swampy environment.

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Since 1862, Schillarization of

has been studied extensively using various methods, such as optical and electron microscopes. The theories on the origin of Schillarization may be classified into two; diffraction and dispersion theories. The diffraction theory was first put forward in 1921 by the late Prof. S. Kozu of Tohoku Imperial University, who studied both adularia and by X-ray and found that was crypto-perthite and adularia potash feldspar, denying the long-holding misunderstandings that was a variety of adularia, showing Schillar. Therefore, it is suggested that the term adularescence which has been carelessly used among gemmologists should be abandoned. Fig.10 A shows the Laue pattern of from Shrilanka which consists of double spots due to albite and orthoclase, definitely showing that is crypto-perthite. When this sample is heated up to 1088℃, the Laue pattern changes to a single crystal pattern as shown in Fig.10 B, exsolution pattern and Schillar effect disappear simultaneously. Kozu therefore believed that Schillarization of. is due to the optical diffraction from crypto-perthite lamellae. The lamellae have been also observed under the electron microscope. The dispersion theory was put forward by Spencer (1930) and Raman (1950), though the latter used a term "diffusion", instead of dispersion. Both did not present enough evidence to support their theory. Now, let's compare the Schillar and texture of with those of labradorite. Labradorite consists of regular lamellae whose thickness changes with the composition, and color, irridescence, changes with the thickness. On the contrary, consists of fine alternating lamellae of albite and orthoclase whose thickness varies from lamellae to lamellae, depending not on the compositions. Albite lamellae show fine albite twinning. The colour of from most localities is blue or silky white. It is clear that the optics should be different between and labradorite.Fig.15 shows a sketch of a simple experiment applied to from Shrilanka. A narrow light beam transmitting through the crystal normal to the (001)(arrow) is reflected by the perthite lamellae parallel to the (8^^-01), resulting in an elongated band of light in one direction. When viewed from the upper side, blue(青), white(白) and red(赤) colours is seen on the cleavage surface as apart from the point of emergence of the light beam. Similar experiment was carried out using a cylindrical screen, a specimen being positioned at the centre of the cylinder. Fig.16 shows intensity distribution of light on the screen. A peak is observed at 60°,which correaponds to the odd times reflection from (8^^-01) perthite lamellae, whereas a broad peak appearing near 0°is due to the even times reflection from the lamellae. The colour on the screen changes with the thickness of specimens. It is bluish when the apecimen is thinner than about 1mm, and is silky white for the crystal of 1 to 5mm thick, and reddish for thicker specimen than about 5mm. Since the phenomenon is very similar to the scattering of sunlight in the sky, it is conjectured that the origin of Schillarization of is dispersion of light due to the lamellar texture. When dispersion is weak, the colour is blue, and when it is strong, it is reddish. If dispersion is medium, the colour is silky white. Figure 17 shows an electron micrograph of a thin foil parallel to the (001) of from Shrilanka. Albite lamellae with fine polysynthetic twinning and orthoclase lamellae have very wavy and irregular interfaces and varying thickness. The orientation of reflection and refraction will slightly deviates from those expected for the reflection of real (8^^-01) lamellae. Since the reflection and refraction are repeated many times in the , the light will become to show the nature of

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月長石は青～乳白色の閃光(シラー)を放つアルカリ長石類(アノーソクレース)である。Na長石とK長石はラメラ状組織を示し(Fleet・Ribbed, 1963)、青白いシラーの原因は(801(－　))に平行な板状組織内に入射した光が反射と屈折を繰り返すことによっておこる光の散乱(秋月, 1976）だとされている。他にも月長石の組織とシラーの対応関係を推測した報告はあるが、シラーの光学的特性やそのスペクトルは報告されていない。 本研究ではU-stageを用いシラーの光学的方位、シラーのスペクトル分析、光学と電子顕微鏡による組織観察、化学分析によって月長石シラーの特性を明らかにしてシラーと微細組織との対応を考察する。試料にはノルウェーのオスロ地域に産するモンゾニ岩(ラルビカイトと呼ばれる石材)に含まれるアノーソクレースを使用する。

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The welded pyroclastic deposit of rhyolite exposed in southwest Toyama Pref. has been considered to be the uppermost member of Futomiyama formation being covered by the basal conglomerate, Nirehara formation, of Neogene formations unconformably. The result of geological study by the writers shows, however, that the rhyolite is embeded in Nirehara formation representing a product of the earliest Neogene volcanism prior to the eruption of a large amount of andesite in the following Iwaine stage. The result is consistent with that of K-Ar dating which gives the mineral age of the as 24-25 m. y.

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Colorful luminescence images were obtained from some feldspar slices after X-ray irradiation. According to a ternary diagram of feldspars, afterglow color images (AGCI) were generously distinguished into two groups, giving intensely bluish or green coloration along the alkali feldspar (Or-Ab) line and weak reddish coloration along the plagioclase (An-Ab) line. In the former feldspar group, blue AGCI samples can be attributed to ordered crystals formed at a relatively slow cooling rate, whereas reddish AGCIs could be assigned to disordered crystals, presumably reflecting a rapid cooling process at formation or thermal alteration. In a microcline, alternative patterns of AGCI are closely related to a perthite structures, consisting of matrix microcline parts and stripe albite phases. Thermoluminescence color image (TLCI) patterns showed blue coloration similar to AGCIs in alkaline feldspars. Among the present feldspars, no homogeneously distributed luminescence existed. On the basis of the present results, the necessity for a single aliquot technique is emphasized for luminescence dating using feldspars.

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スリランカは, 宝石の種類が最も豊富なことで有名であるが, いずれも漂砂鉱床に産し, 不思議なことに原岩はまだ発見されていない。地質は大部分先カソブリア紀の地層よりなり, Highland層群, Southwest層群, Vijayan層群に3大別できる(図参照)。主要宝石産地は, Sabaragamuwa州のRatnapura地方, 中央州のElahera近傍, 南部州のTissamaharama地域である。これら主要産地での採掘法, 宝石鉱物種, その中にみられる包有物などについて説明した。

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Oligocene to Miocene volcanic rocks from the Toyama basin of the SW Japan arc, that were formed during back-arc spreading in the Japan Sea, were examined to reveal their petrogenesis and temporal change of arc volcanism during the Japan Sea opening. The arc volcanism in the Toyama basin initiated with rhyolitic pyroclastic flows (Tori Formation) containing hecatolite (

) in 23-22 Ma. Enriched Sr-Nd isotope (SrI = 0.70769-0.70944; NdI = 0.51203-0.51224) suggests that contemporaneous andesitic magma (Kamiwazumi and Matsunagi Formations) mixed or assimilated basement granitoids and gneisses of the Hida belt to generate rhyolitic magma. Subsequently, andesitic volcanism (Iwaine Formation) occurred in 18-17 Ma after magmatic hiatus. Andesitic lavas of the Iwaine Formation are composed of high magnesian andesite (HMA), high-Sr andesite and tholeiitic andesite. HMA has Mg# > 64, high Cr and Ni concentrations, not so high Th/Yb and (La/Sm)_N ratios, and slightly enriched Sr-Nd isotope (SrI = 0.70482; NdI = 0.51279). High-Sr andesite has relatively low SiO₂ content (<60 wt%), high Sr (>2000 ppm) and K₂O contents (3.98 wt% in the maximum), indicating that it is low-SiO₂ adakite. These geochemical characteristics suggest that HMA and high-Sr andesite were produced by partial melting of the mantle wedge saturated by H₂O derived from slab fluid and metasomatized by slab melt, respectively. Although chemical variation diagrams suggest tholeiitic andesite seems to have been generated from basaltic magma, it has enriched Sr-Nd isotope (SrI = 0.70713-0.70756; NdI = 0.51237-0.51241). Thus, tholeiitic andesite is considered to have been produced by AFC (assimilation and fractional crystallization) after generation of basaltic parental magma. Andesitic magmatism of the Iwaine Formation was followed by rhyolitic magmatism of the Iozen Formation in 17-16 Ma. The petrogenesis of the rhyolite from the Iozen Formation can be explained by low-rate mixing between andesitic magma (Iwaine Formation) and the Hida belt. The petrogeneses of the andesites, especially HMA and high-Sr andesite, are related to slab melting. Because the old and cold Pacific plate was subducting beneath the Toyama basin during the Japan Sea opening, additional heat source such as upwelling of the asthenospheric mantle into the mantle wedge is required. Moreover, back-arc spreading in the Japan Sea was driven by upwelling of the asthenospheric mantle into the mantle wedge.

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