Selling a chunk of granite?

while walking around a pond that no one really knows about in back of my townhouse, my friends and i found a nice sized chunk of rock that appears to be granite according to this picture: http://www.beg.utexas.edu/mainweb/publications/graphics/granite-400.jpg except ours is more rounded at the bottom and has... show more while walking around a pond that no one really knows about in back of my townhouse, my friends and i found a nice sized chunk of rock that appears to be granite according to this picture:

http://www.beg.utexas.edu/mainweb/publications/graphics/granite-400.jpg

except ours is more rounded at the bottom and has pieces of crystal in it. where can we sell this and how much would we get from it?
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