Chrisson

I came back from a vacation and brought home a bunch of rocks. I think if placed right they can look really good in an aquarium so I was wondering if these rocks are safe. I did a vinegar test and it didn't fizz but just making sure...

prairielilly

they're sandstone, so yup they're safe Likely all or mostly silica (SiO2) which is completely inert. We melt it down to make glass, and if you're using regular gravel or sand likely the majority of it is the same stuff.
Nice ones, too. That'll make some great aquascaping

Edit: there's a small chance they're dolomite (but I still think they're sandstone..) Try to scratch one with a steel knife. If you can, it may be dolomite. If you can't, they're sandstone.

Chrisson

No scratches happening so it must be sandstone. thanks for the info! I'm gonna start changing my aquariums around tomorrow!