A rock fragment between 4 and 64 millimeters(0.16 and 2.51 inches) in diameter, especially one that has been naturally rounded.是什么意思_A rock fragment between 4 and 64 millimeters(0.16 and 2.51 inches) in diameter, especially one that has been naturally rounded.在线翻译_英语_读音_用法_例句