Is it volcanic? These can be grey, black, red and perhaps other colors. It is occasionally very sharp. Volcanic rocks can look like they are very bubbly.
If you put it in water does it raise the pH, KH and GH? This would suggest a limestone sort of stone. These are usually white or almost white. This picture looks too grey. There is a form of limestone called Tuffa. It can have holes that might look like had boiled like volcanic rock, but it is actually from acidic water eroding the rock. Limestone sorts of rock are very common, found all over the world. Marble is one form of Limestone.
One place that limestone is common is in Texas, USA. When this material is sold for aquariums it is called Texas Holey Rock.
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