Hey everyone, I'm trying to rescape a 20 gallon and wanted to add some nice pieces of hardscape. I braved a blistering sun and extremely cold water possessed by a mighty current to grab some of these choice pieces. Granted the water was at most only 4ft deep but none the less, it was an adventure of epic proportions : )
Here they are:
I tried to stay away from yellowish rocks that could contain calcite but the majority of the rocks do have shiny flecks (pyrite?) in them, some more then others. Do I need to cull all these out or can I keep them?
what you do is test them. use the nitrate #2 bottle from your API test kit and place a drop on the rock, if it bubbles up then you have a rock that will raise the ph of your tank and throw it out. if no bubbles then its a "neutral" rock and safe to use. you can also use vinegar if you don't have an API test kit but vinegar doesn't show the bubbles as well.
Based on what I can see in the photos you look to have a mixture of granites possibly gneiss, and possibly some sandstone and mudstones. As stated above get some acid to betermine if they contain Ca [lime stone]. As far as the Shiney flakes they are most likely mica, since you have some igneous and metamorphic rocks. Don't worry about them as they are basic silica minerals.
One additional thing just because it's a river rock does not mean it's safe. I know places where the rivers are dead because of the rocks that are in them. Never assume just because the rock is in the river it's inert.