Magma is the molten rock and minerals found beneath the surface of a planet which makes up much of the mantle.
History and specifics[]
On the planetoid Darien 224, when an ancient Vulcan psionic weapon, the Vorl-tak, was fired it caused an energy feedback which shattered the planetoid’s mantle which began to sink into the magma layer. (EV comic: "Cloak and Dagger")