Advertising exec Gary Dahl was in a bar in Los Gatos, California, in 1975 listening to his friends complain about their pets. He joked that a rock didn\’t need to be fed or walked, and would never die. He took the idea home with him that night. He bought a bunch of gray stones at a building supply store (and eventually imported them from Mexico at a penny apiece), put each into a straw-lined box that was designed like a pet carrier, threw in a 32-page manual on the care and training of a pet rock, and started selling his rock-in-a-box for $3.95. The fad lasted six months, from mid-1975 to the Christmas season, just long enough to make Dahl a millionaire. He used the money to open his own bar in Los Gatos.

Source

quoted from Uncle John\’s Bathroom Reader: History\’s Lists, \”It\’s Contagious!\” page 224.