denis coghlan
Fishaholic
It looks like limestone, is it limestone? or what is it?
all my rocks limestone and that doesnt look anything like it.
wolfs rock thread should help you ID it.
When I asked about the stone, I was talking about the stone that mark had collected in his picture. The stone in the pots on my cooker is old red sandstone. Mark limestone is not necessarily crumbly or brittle, in fact it can be downright tough to break. From the look of your rock, “I am no geologist now” but I’d say it is a sedimentary rock classed as a tillite, this has a compacted structure of smaller (tiny) particles (of other sedimentary rock usually limestone) constructed at various angles and bound together, colour varies from brown to grey to greenish black. I think that is should be ok in the tank.
Got the info out of a book called Minerals, Rocks and fossils by W.R. Hamilton (very nice book actually lot of pictures)