I couldn't find the definitions from either source:
I'm quoting from my old The Penguin Dictionary of Geology by D. G. A Whitten & J. R. V. Brooks, published in 1979.
Rock (1) To the geologist any mass of mineral matter, whether consolidated or not, which forms part of the Earth's crust ... (2) The civil engineer regards rock as something hard, consolidated, and/or load bearing, which, where necessary, has to be removed by blasting. This concept also accords with the popular idea of the meaning of the word.
Stone In geology the word 'stone' is admissible only in combinations such as limestone, sandstone, etc., or where it is used as the name for extracted material - building stone, stone road. It should not be used as a synonym for rock or pebble.
Most sources say that rocks are made of stones. (Or at least that stones are rock fragments.)
From the Bing dictionary (definition of stone):
- hard nonmetallic material: the hard solid nonmetallic substance that rocks are made of.
- rock fragment: a small piece of rock of any shape
- shaped rock fragment: a piece of rock that has been shaped for a particular purpose, e.g. a gravestone
Quoting from a blog post by David B. Williams on geologywriter.com
... The first definition for rock is “A large rugged mass of hard mineral material or stone.” ... defines stone as “A piece of rock or hard mineral substance of a small or moderate size,”...
Some other things people think distinguish the two:
...some people thought that stone was more British; that rock could be hard and soft, whereas stone was always hard; that stones are smooth and rocks rough; and that stones are small and rocks are big. In his wonderful book, Stone by Stone, Robert Thorson writes “Rock is raw material in situ. Stone usually connotes either human handling or human use, although it can also be used to describe naturally produced fragments of rock larger than a cobble.”
(Quoted from that same post mentioned above)
- A rock is a large stone - immovable by hand possibly
- Rock is made up of stone in the sense where stone is a substance
- Stones are fragments of a rock also made up of stone but are themselves objects
The problem here is differentiating between a stone and stone. One being an object and the other a substance? Once clarified then the difference between a rock and a stone can be possibly be clarified.
So to answer the question above - yes there is a difference - a rock is an object and stone is a substance.
If the question was 'is there a difference between a rock and a stone' then size or weight could possibly be the answer.
The definition I've seen before is one of context.
You know where a rock came from - eg. you may have recorded it in your field notebook.
A stone has an unknown origin - eg. stones on the road, in a river, etc.
As such, I guess most glacial erratics are technically stones rather than rocks :-)