This should answer a few questions about Pyrites there's a link also , below is whats quoted in the link . Good luck great find
It can be tricky to the beginner! Below I have added some pictures that show the differences in common pyrites found in Arizona and Arizona gold. I detected all the gold you see in the pictures below with using either a White's GMT or a Minelab GP Extreme. Click the pictures to enlarge them. Some of the pieces of gold pictured below I have never shown before making this web page. All the gold below is specimen gold they are not nuggets. The reason I used specimen gold is all of the pictures I am sent always have "host rock" in them. You cannot "flake" gold off a rock with a knife, if you hit gold in rock the rock will break/shatter but the gold will flatten/bend. Pyrite if struck with a hammer will shatter/crumble.
http://arizonagoldprospectors.com/goldandpyrites/metaldetector.html