I am no gold mining expert! I have only found 1 good small gold nugget little bigger than the size of a thumbnail and it was by luck in Canada!. Anyway, i'm pretty sure it is just pyrite.. I see rocks just like this one all over near lakes,rivers etc when I up too Canada to go hiking.. We have quite a few experts here who know more about this then I do but you should be able too buy a gold test kit and break the rock up and test it. Done it plenty of times probably 500 times with rocks like these and never ever have hit a trace of gold.