• Sand -> Gneiss Sand change, with Gneiss Sand just being oredicted as being Sand (though it probably shouldn't be able to be turned into Sandstone for obvious reasons).
• Replace the Savannah's stone boulders with Gneiss boulders for the sake of in-mod consistency
• Only the dungeon-related Gneiss blocks should turn into Lava when broken, probably.

Sand I agree with.
Stone boulders should stay as is - Gneiss doesn't belong/fit there. Stone is more fitting.
Making only dungeon blocks create lava could be a thing, but involves making more superflous blocks or code for something odd ( I mean the gneiss boulders should as well).