I really want to go back to around Duluth and look for rocks again. I had been there almost a week before I found out what awesome rocks they have. Like lots of agates.
I started that way too. I found some weakly fluorescing rocks in decorative rocks around my inlaws house.
If you go you might still try to get a cheap Shortwave UV lamp. Black lights are long wave and some rocks only glow or glow better under shortwave.
Though black lights are a good place to start. With it being Halloween soon, check the local stores. I found a portable ~6" battery powered UV lamp at Target one year for like $5. The batter pack tabs have broken, but I fixed it with tape.
