I have tried 3 times to complete the game. I have all the puzzles finis…

I have tried 3 times to complete the game. I have all the puzzles finished but am lacking only 1 rock in my collections. I have been staring at the computer non stop for 3 days, keeping my eyes open for the last rock. NO ROCK! This is the only thing keeping me from finishing the game. I am beginning to think there is no such rock! What should I do???