I'm sure there are many articles out there that cover what Rocks are safe for Aquariums? Here in the rockies we have these riverbeds that are a collectors dream? I know many retailers would like you to pay big bucks for approved rocks which are fish safe? I know you have to watch what you use because many fish come from say very akaline water or vice versa. I look at it this way trout and salmon are a very sensative fish and in most cases if they are thriving in a particular river then its a pretty good chance its safe for my fish. I remember as a boy in Maine we used to collect hugh pieces of Pink and white Quartz (I mean the stuff is beautiful!!) I was at a show not long back and do you know how much they wanted for a large piece of Pink Quartz ($$$). So for those of us who are cheap or just love to use it as a excuse for a day collecting on a beautiful riverbed somewhere is there a easy rule to go by if a particular rock is safe?