The geology and K-Ar geochronology of the Gassan volcano in Northeast Japan were carried out to establish the volcanic history.
     This volcano is belonging to the Chokai volcanic zone, and composed of several volcanic edifices. On the basis of the field geology and K-Ar dating of the ejecta, the volcanic history is divided into five stages;
     Stage I (0.88 Ma): the Amamoriyama was formed by dacite volcanism. The dacite lava is composed with hypersthene, augite, hornblende, biotite and quartz phenocrysts.
     Stage II (0.7 Ma): The Yudonosan, which is composed of a stratovolcano and two lava domes of mainly dacite lava and pyroclastics.
     Stage III: The volcanism occurred in the north of the Yudonosan. The dacite lava and pyroclastics covered on the basements in the caldera and the lower Yudonosan lava in the Ishihane river.
     Stage IV (younger than 0.6 Ma): The volcanism of the major stratovolcanoes of central Gassan, the Waratahageyama and the Ubagatake, which are composed of lavas and pyroclastics. The rocks are calc-alkali andesite containing hypersthene, augite, sometimes a small amount of olivine and rarely hornblende.
     Stage V: The collapse of the northwestern half of Gassan stratovolcano, caused the formation of a horseshoe-shaped caldera and dry avalanche deposits.
     The rocks of the Gassan volcano are divided into two groups, dacite and andesite in their temporal as spatial distributions.

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西之表市に分布する形之山層の頁岩中に，小さな塊状のリンカイ石が産出する。この塊は，固く，一見頁岩のノジュールのようにみえる。リンカイ石は硫黄を含んでおり，この硫黄含有リンカイ石について，鉱物学的データを得た。形之山層にリンカイ石が産することから，この頁岩層は多くの哺乳動物や魚類の骨と一緒に堆積し，堆積後の続成作用の過程で，この頁岩層と哺乳動物や魚類の骨との反応で生成したと考えられる。

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1470-1570 K/6GPaで合成した，NaScSi₂O₆-CaZnSi₂O₆系の8種類の単斜キ石の結晶構造を，単結晶X線データをもとに精密化した。これらは他のNaキ石あるいはCaキ石と同型であり，空間群はC2/c，Z=4で，ScとZnは歪んだ6配位席（M1サイト）を占有している。O1-Si-O2角とd_br-nbr距離との間には2種類の相関性があり，電子状態の異なる2種類のZnイオンの存在を示唆している。なお，d_br-nbr距離は平均Si-O（架橋）距離と平均Si-O（非架橋）距離の差である。

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