Hyaloclastite (English spelling)

Japanese: ハイアロクラスタイト（英語表記）hyaloclastite

A type of water-cooled, fractured pyroclastic rock, named by Rittman for glassy rocks formed when the surface of magma comes into contact with water and is rapidly cooled and fractured [Rittman: 1960]. Like pillow lava, it is commonly found accompanying lava that has flowed underwater, and is often basalt, but recently the term has come to be used to refer to water-cooled fractured surface material such as underwater lava and dikes of all compositions [Katayama et al.: 1970, Geological Society Research Association: 1996]. When lava enters water, it undergoes a dramatic phreatic explosion, rapidly cooling and simultaneously breaking into small fragments, which are stretched, broken, and deposited. A general term for glass fragments of various sizes contained within even finer clay-like material.

Source: Asakura Publishing Dictionary of Petrology Information

Japanese:

水冷破砕された火砕岩の一種で，リットマンが水と接触したマグマの表面が急冷され破砕されて生じたガラス質の岩石に命名した［Rittman : 1960］．枕状熔岩のように，水中を流れた熔岩を伴って普通に産出し，玄武岩のものが多いが，最近はすべての組成の水中熔岩や岩脈などの表面の水冷破砕物にも用いられるようになった［片山ほか : 1970，地学団体研究会 : 1996］．熔岩が水中に入ると著しい水蒸気爆発を起こし，熔岩が急冷して同時に小さな破片となり，引き伸ばされ破壊して堆積したもの．様々な大きさのガラスの破片が更に細かい粘土質物質中に含まれるものの総称．

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