Using Black Sand

[Sea Witch]

I'd like to ask about black sand. Correct me if I'm wrong, but the black sand is not calcium-based, it's volcanic rock.

So is it a problem if you don't have the buffering capacity of the calcium sands?

Is it still useful for a DSB?

And is it sharp-edged instead of round-edged? i.e. is it a problem for digging critters or fish like a jawfish?

I really like the way it looks, but I won't use it if it's harmful........

thanks