Wavy extinction in quartz is a good indicator for the magnitude of deformation. The intensity of wavy extinction (IWE) in quartz was quantitatively measured using polarized optical microscope, digital camera and NIH Image. Quartz-grain showing a maximum interference color is appropriate for the measurement of IWE. A traverse for the measurement is set across the parts showing distinctive wavy extinction, where subgrain boundaries in deformed quartz generally intersect with the line. The brightness of each part showing wavy extinction is measured at the extinction position of a subgrain. A gradation of brightness is treated as 256 gradient in computer. IWE is defined by the formula, IWE=tan (magnitude of brightness/1000*length of the line for measurement), where the length is scaled by millimeter. Based on this method, we can give an intensity of wavy extinction to deformed quartz grains, and it has been shown that the mylonitic and weakly mylonitized granitic body adjacent to the Tanakura shear zone in northeastern Japan can be divided into several zones of deformation intensity. This method can be applicable to many kinds of deformed minerals to describe the degree of deformation.

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日本国マイロナイト及び岩船花崗岩の全岩及び鉱物組成をXRF， EPMAを用いて測定した。岩船花崗岩はマイロナイト帯の両側に分布し，日本国マイロナイトに漸移し，全岩化学組成及び鉱物組成も重複するのでその原岩である。従って，日本国マイロナイト帯は棚倉構造線の北方延長ではない。日本国マイロナイト構成岩類（片麻状角閃石黒雲母花崗閃緑岩，片麻状黒雲母花崗閃緑岩，片麻状黒雲母花崗岩）及び塊状黒雲母花崗岩（岩船花崗岩）はハーカー図上で直線的なトレンドを示し，SiO₂ は，この順に増加する。黒雲母のMg/(Mg+Fe）値及び斜長石の灰長石成分はこの順に減少し，それぞれ，全岩組成と相関する。従って，日本国マイロナイト構成岩類及び岩船花崗岩は，成因的に一連のものであることが示唆される。マイロナイト中の細粒再結晶黒雲母は，もとの粗粒結晶よりもTiに乏しく，マイロナイト化作用の再結晶温度がマグマ結晶作用時よりも低かったことを示している。
Ganjiki 岩石　Ikazuchi 雷　Miomote 三面　Nakatsugi 中継　Nezugaseki 鼠ヶ関　Omata 小俣　Onabe 小名部　Sekigawa 関川　Tanagura 棚倉　Yamakumata 山熊田

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Minute hexagonal platy crystals in druse of pyroxene andesite from Taihakusan, Sendai were examined by polarized optical microscope, SEM, EPMA and X ray studies. Although the mineral looks like trydimite, X ray analyses (microdiffraction and precession camera) demonstrate it to be cristobalite. It is assumed that the cristobalite crystals with fine stacking faults and polysynthetic twins were produced in the druse from a gas phase after andesite was solidified.

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