It can and often does. Not always but often.
as far as details, what makes lava??
magma, right??? what is magma made of?
minerals and ores
to include:
copper
zinc
iron
silver
to name just a few.
You name it, it can be in there, dependig onwhere the rock came from will depend on what minerals it consists of. It does not take an expert or geologist to figure this out. But many people may not know this but many minerals are hazardous in SW tanks, in particularly towards inverts more than fish.
As for the shops, well who said they know their stuff? May of them bash LR, end even more slam a DSB. And how many of them sell mandarins and anemones and Moorish Idols, and could not keep either for a month themselves.
Lava, it works great for fresh water, but is severly RISKY for salt. It is not a guarentee, but my biography is titled: 'Murphy's Law', so I would not chance anything like that at all.
Oh, and being a business, esp the chains, would not pull it off their shelves, esp since it does sell but mostly to those who do NOT know any better. Grociers never pulled tobacco off the shelves ,did they? No, not even after it was proven it will kill us, if we use it. I can name many many other examples. Money talks, .................................................