Advice needed from the fish community on tank-safe decorative crystals
I've been trying to think of different ways to decorate my betta fish tanks and have seen a few with crystals in their tanks (semi-precious stones, such as quarts and amethyst). I think they look gorgeous, but I'm wary to just put whatever I have into them. I know that sometimes toxins can leech into the water and the last thing I would want to do is kill my fish. I've asked a couple of people and they say quartz and amethyst are fine, but in general I've been hearing conflicting information. Quartz seems safe, but I've heard that amethyst isn't? Could someone please help me figure out what's safe to use and what isn't?
I would also love some articles supporting your suggestions, whether pro or con. I want to be able to make the most educated decisions for my fish to continue leading happy, healthy lives.
(Also, if porcelain/ceramics and resins are safe. I keep seeing cute figures on Etsy, but again, better safe than sorry!)