Volcanic gravel - lapilli

Japanese: 火山礫 - かざんれき（英語表記）lapilli

Pyroclastic material ejected by volcanic eruptions, with a diameter of 2 to 64 mm. Also called lapilli (singular lapillus). Smaller particles are called volcanic ash, and larger particles are called volcanic blocks. Among lapilli and volcanic blocks, those with a specific shape (structure) such as spindle-shaped or spherical are called volcanic bombs, and those that are porous are called pumice (floating stone) or scoria. Pyroclastic rocks that are mainly composed of lapilli are called lapilli stone, and those that are mainly composed of lapilli and ash are called lapilli tuff.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

火山の噴火で放出された火山砕屑物のうち，直径 2～64mmのもの。ラピリlapilli（単数 lapillus）ともいう。これより小さいものは火山灰，大きいものは火山岩塊である。火山礫，火山岩塊のうち，紡錘状であったり球状であったりするなど特定の外形（構造）をもつものを火山弾，多孔質のものを軽石（浮石），スコリアと呼んで区別する。火山礫を主とする火山砕屑岩を火山礫岩（ラピリストーン），火山礫と火山灰を主とする火山砕屑岩を火山礫凝灰岩（ラピリタフ）という。

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