Yes, its fine. I previously used large 'chunks' of Lava Rock that I bought online from Germany and shipped to the UK. (Approx 10 inches).
I carefully balanced a group of these together about 3 high to create a curved wall in my 225 Gallon setup. Im sorry I dont have a photo to show you, the tank is no longer setup like this. No due to the Lava rock I might add. It was due to a house move.
I found my plecs would not go near it, too rough and sharp on their belly. but other fish would hide behind the wall etc.
Ive also heard it good for creating an anaerobic area within the lava rock that helps convert nitrates etc., whilst aerobic bacteria coat the outer layers of the lava rock helping to convert ammonia, nitrites.
Java moss etc sticks well and looks the part and can be useful to quickly aquascape a tank etc.
Hope this helps.