Can anyone recommend what type of rock would work to line a fire pit? I am looking for a type that is unlikely to explode when heated.
When I built a pit to roast pigs in some years ago, my brother brought up a bunch of lava rocks from southern Oregon for me to line it with. What you don't want are river rocks. Basically you're looking for rocks with rough edges instead of rounded. Rounded indicates the rock has been smoothed by water action and may contain water which as you've indicated can possibly explode from steam building up inside it.
Before I ever used my pit, even though it was made with lava rocks, I built a couple of small fires in it to slowly dry out any rocks that may have possibly had any water in them.