507 Carat Diamond found. Big, honkin' diamond!
This diamond was found in the Cullinan mine in South Africa. Recognize the name? Other famous Cullinan diamonds would be the Greater and Lesser Star of African (Cullinan I and II) in the Crown Jewels of England - both cut (along with other stones) from a 3,106 carat piece of rough.
Check out the story here, and the photo gallery.
Looks like a big ol' hunk of quartz, doesn't it?