There are several methods mostly involving some pretty harsh chemicals, you DON’T want to try these.
Easiest (safest) way is to put it in a cast iron pan and take a hammer to it; pyrite, mica, etc will shatter into fine grains or dust.
Gold is malleable in it’s natural state, it will flatten and spread out (like a piece of soft copper) instead of breaking up.
If your still at the stream and your looking at the rock in the sunlight and it looks shiny and gold, it MIGHT be; put your hand between your specimen and the sun (put the specimen in good shade), does it still look shiny and gold? It MIGHT be, further tests are required.
But see somebody who knows what their doing before you get into NITRIC ACID tests, NITRIC ACID is a very dangerous chemical to be messing with unless you know what your doing.
thanks!