I got a whole lot of rocks from down by the Waimak (in chch) and just want to check if they are suitable for my freshwater tank. They aren't riverstones, I think they have been brought in from elsewhere to build the stopbanks?
I'm pretty sure it's some sort of igneous rock, it's quite holey in some places, like it was air bubbles in the rock.
I read somewhere to check it with white vinegar to see if it fizzes.... just have to buy some vinegar first....
here's a pic, does this rock look ok??