nouns - What's the difference between "rock" and "stone"?

What's the difference between "rock" and "stone"?

Answer

A rock is bigger, possibly immovable, you couldn't throw it with one hand, at a pinch you might be able to with two.

Above, a Google Image result for "Rock", below, for "Stone"

Note that a boulder is probably bigger than a rock¹.

Below, a boulder

Oh, also note that rocks and boulders are made from stone.

(This answer is mildly tongue in cheek)

¹ Notable exception: Uluru/Ayre's Rock.