A fire pit installation in Hawaii uses basalt reinforcement rebar to take the heat!
Lava rock calls for lava rebar. Basalt lava rock fibers make reinforcements that expand and contract at the same rate as concrete unlike other fibers. Also, poly fibers and fiberglass fibers can not take extreme heat as well as basalt and costs more.
Our basalt rebar comes in coils so making a shape like this firepit would be very easy. No bending of steel to figure out. Mahalo Jim nice job!