Is there a difference between rock and stone?
I'm quoting from my old The Penguin Dictionary of Geology by D. G. A Whitten &amp; 
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.