GeologyRocks

Someone gave this to my wife about 10 years ago it spent the last 5 years outside in a weed bed all I can tell you is its about 12" x 8" x 6" and it weights 17lbs. there is a lot of air bubbles in it you can see throught it like in the last pic you can see my hand throught it and in one part of it i think i can see a blade of grass in it . it also has some sharpe edges. My wife said that the person that gave it to her stated it came from Arkansas hot springs area he found it on the ground . what is it and my last question is what is it worth.