I think the first thing is to go to the strobist site and glean as much off there as you can.
http://www.strobist.blogspot.com/
but it sounds like you have the right general gist of the solution... the strobist might help also with suggestions such as using a snoot to isolate the rock, or a gobo to create mottled light patterns... etc etc etc.
also probably you'd want to light it from an angle to avoid the " deer in the headlights" flash from front feel... the strobist is pretty good for that off camera flash stuff too