When Does a Stone Become a Boulder?

In geology (Udden–Wentworth scale), a boulder is a rock fragment with size greater than 256 millimetres (10.1 in) in diameter. Smaller pieces are called cobbles and pebbles.

What classifies a rock as a boulder?

A boulder is defined as any rock larger than 16” in diameter. They are available in two basic shapes: round and angular. Round boulders have smooth edges and curves. They are water-washed or river-run surface stones of granite and sandstone, worn over the eons by wind, sand and rain.

What is the difference between a rock a stone and a pebble?

Rocks are made of smaller stones and stones are made from rocks. Rocks can be described as a large piece of stone that is difficult to be carried in the hand. On the other hand, stone is just a small piece or pebble that can be carried in the hand. The rocks are heavier than stones.