What is the difference between 'rock' and 'stone'?

Doctor Rock,
Do geologists distinguish between 'rocks' and 'stones'? Are these terms interchangeable?
Louisa Mayfair
Winnipeg

Louisa,

"Hey, Callie, is this a rock or a stone?'
"Not sure, Alec, let's ask Dr. Rock!"

Nice to hear from a reader in the 'True north strong and free'.
The difference depends on the context. In the informal usage, if you apply these terms to individual pebbles or boulders, then there's no difference. You can pick up a 'rock' and toss it in the creek, or do the same with a 'stone'. However, to a geologist, that pebble is made of 'rock'.'Rock' is the accepted scientific term for the material that forms the earth's crust and deeper layers. Geologists have a simple and somewhat facetious way to distinguish between 'rock' and 'stone'. If a price tag is attached, it is a 'stone'.

Here are definitions from the Dictionary of Geological Terms ('DGT') published by the American Geological Institute:

My friend Adena is standing behind a large conglomerate
boulder. This is a 'rock' using definition 1. of  'rock'.
According to definition 2 under 'stone', this
sedimentary rock consists of many rounded stones. Click
the photo for a closer look.

'Rock' 1. an aggregate of one or more minerals, e.g. granite, shale, marble or a body of undifferentiated mineral matter, e.g. obsidian, or of a solid organic material, e.g. coal. 2. Any prominent peak, cliff or promontory, usually bare, when considered as a mass, e.g. the Rock of Gibraltar. 3., A rocky mass lying at or near the surface of a body of water, or along a jagged coastline, esp. where dangerous to shipping. 4. a slang term for a gem or diamond.
(Doctor Rock adds: "I am aghast that they left 'Led Zeppelin' out of this definition! And what about the Stones?")

'Stone' 1. A general term for rock that is used in construction, either crushed for use as aggregate or cut into shaped blocks as dimensional stone. 2. One of the larger fragments in a variable matrix of a sedimentary rock. 3. A stony meteorite. 4. A cut and polished natural gemstone; a gem or precious stone.

There are interesting variations in nongeological dictionaries. For instance, the Random House Collegiate Dictionary says, among many other things, that 'stone' is "1. the hard substance, formed from mineral and earth material, of which rocks consist." (There are 27 more definitions!) Under 'rock', that dictionary's first definition coincides with definition 2. in the DGT. The second is the 'geological definition', essentially the same as 1. in DGT.