Does it feel granular and rough, can you feel a gritty substance when you rub it between your thumb and finger? Looks like a pale form of sandstone to me. Limestone is pale grey, but has a much closer, smoother texture. Acid poured onto limestone fizzes, but I wouldn’t try that if your going to use it in the pond!
I was going to guess sandstone as well. Any geologists on here? I'm wondering if there are different types of sandstone. The "fieldstone" I have is sandstone, due to where they got it (here in the south, I assume.) My pH stays right at 8, no matter how often I do or don't change the water -- and no matter how much I feed or don't feed the fish. So the rocks I have seem to be working well! Your pond looks great!
If it was limestone an odd piece or two wouldn’t have any effect on a pond of that size. If you think about the formation of stalagmites and stalactites they take a vast amount of time to form from the minerals that are leached out of the surrounding limestone by the rain flowing over them. Limestones are pale in colour due to their mineral makeup...calcium carbonate from coral, shell and animal remains...they’re dense and hard making them heavy, they don’t break easily and often contain fossils.
Sandstone comes in different colours, and with different granular structures too. My house is built on a sandstone ridge and I can dig down to solid red sandstone in several places. Some is close grained others have the look of granulated sugar almost. Because it’s made of compressed sands, it often has layers and can be broken easier than limestone.
Mmmmmh, what was the conclusion? Didn’t fizz much did it, if at all, so could be sandstone. Maybe your vinegar was the problem, acetic acid may not be strong enough....was it Sarsons? Lol!
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