pebble

The children spent the afternoon skipping flat pebbles across the calm surface of the lake.

(Chinese) 孩子们整个下午都在平静的湖面上打水漂，用的是扁平的鹅卵石。

Walking barefoot on the beach was difficult because the shore was covered in sharp pebbles.

(Chinese) 在海滩上赤脚行走很困难，因为岸边布满了尖锐的小石子。