Most gravel purchased at the store is inert any way but any rocks you gather from streams or rivers should be tested.
It's much safer to test with vinegar. If it bubbles it's only safe to use in tanks needing a high pH.
What ever you test with make sure you rinse what you test very thoroughly.
it's mined from the Rocky Mountains by a friend who pans for gold. I've read that vinegar isn't strong enough of an acid to test rocks but I did the vinegar test and it didn't bubble. I just wanted to make sure it's ok.