Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I bought a 1 cubic foot bag of 3/8" diameter red lava at a rock yard.
There is a lot of powder in it, and this will definitely cloud the water.
So I cleaned the lava by washing it in small batches in 5 gallon buckets. I stirred it by hand. The material I got was not very sharp at all. By no means smooth, like river rock, but simple rough texture, not sharp.
If you want sharp there is a grey pumice that is sold as boulders for landscaping. So full of air holes it will float! But SHARP! It will draw blood, and you must use gloves for handling it.
Makes interesting planters for flowers, though. You can work it with simple tools, like an old spoon, and hollow out the stone. (Don't forget the gloves!)