Ya I think quartz would be the best bet, I dont think it leeches anything out. I also like the natural look so thats why I wanted to put some cool/rare rocks or crystals in the tank because they are natural and I've never seen anything like that before. What really gave me the idea was that the volcano rock i bought for the tank had little crystals in it! i was like "hmmmmm"... so I just thought I would ask u guys if you've heard anything or seen anyhting like that. I also was googling around but their wasnt too much info on aquariums+minerals.