For 10 points, name this rock, which forms from rapidly cooling lava into a black, shiny volcanic glass.
A piece of this material that "has no earthly business in a Maine hayfield" hides a letter from Andy to Red in The Shawshank Redemption. After his foot was eaten, Tezcatlipoca replaced it with a mirror made of this material. This material, formed when flowing (*) water meets a lava source block, can be used to construct a Nether Portal in Minecraft. For 10 points, name this rock, which forms from rapidly cooling lava into a black, shiny volcanic glass.
A piece of this material that "has no earthly business in a Maine hayfield" hides a letter from Andy to Red in The Shawshank Redemption.
obsidian (prompt on "volcanic glass" before mentioned)