a rock is larger, stones are hand held, (skipping stones on the water) rocks are 2 handed and larger, ( ok 1 handed if your strong but bigger than your hand.) pebbel stone rock boulder planet. I think that is the order. (at least in my head it is)

As a trained geologist, I have never heard of either rock or stone having a size associated with them. Rock and stone are just general terms. The size categories with which I am familiar are as follows: < 1/256mm - Clay 1/256 to 1/16mm - Silt 1/16 to 2mm - Sand 2 to 4mm - Granule 4 to 16mm - Pebble 16 to 256mm - Cobble >256mm - Boulder

Thanks to Glenn for the technical answer on geological scale of particle sizes... On a lighter note the general relativism of these two terms is clear... "A rock" is commonly used in reference to a large piece of rock being anything from a size that you would have difficulty lifting with one hand up to a very large boulder bigger than a house... "Rock" without the singular "a" is of course a general term for any solid natural mineral substance of any size from a sand grain to a whole planet. "A stone" is commonly used in reference to a small rock such as a cobble or pebble or rock fragment that might easily be picked up in one hand.... "Stone" without the singular "a" in common parlance means rock in a worked or artificially altered form, such as building stone, cobble stones, dressed stone, polished stone, gem stones, mill stone, stepping stones, stone lintels, stone mullions, stone sculptures; a rolling stone gathers no moss, and stone the crows! its also a verb... to stone, to throw stones at (an unpleasant activity particularly for anyone at the receiving end)... Glenn will correct me if I don't say it... In geological terminology "stone" denotes a particular type of rock such as sandstone, limestone, siltstone, mudstone, millstone, whinstone, brimstone, pumice stone... Generally in nearly all cases, whichever way you view em, rocks are bigger than stones....