Reddit mentions of Teroforma Whisky Stones Set of 6

Rocks actually did originally refer to actual stones, and a contemporary version can still be bought: http://www.amazon.com/gp/aw/d/B008ZT2WW2?pc_redir=1398091608&robot_redir=1

These cool without watering down your drink.

These days you can literally have drinks "on the rocks."

http://www.amazon.com/Teroforma-Whisky-Stones-Set-6/dp/B008ZT2WW2

You can use these... I'm pretty sure rocks don't melt in soda.

Neat. Sometimes I'll drop some whiskey rocks in. The cooling from the rocks completely removes any burn from the alcohol without watering down the whiskey.