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1.
A fart rock is actually a rock containing sulfur that you can break, or scrape, to achieve a horrible fart smell.
Someone broke a fart rock in the hallway and it was so bad that they had to close it off for the day.
by Diesel AG April 04, 2009
 
2.
The little piece of poo that is pushed out then broken off during a forceful fart. Similar to poop-nugget and shart. (It is the less wet and messy version of the shart)
"Oh man, I think I just left a fart rock in my jockey's."

"Dude, I can totally smell that fart rock you just dropped. Go to the bathroom and clean that out."
by Heather Dizzle January 21, 2008