Molten material within the Earth is called magma. In simple terms magma can be thought of as molten rock. When magma cools, it solidifies to form rock which is called igneous rock. That is deceptively simple, since the solidification process can be very complex.There is a considerable range of melting temperatures for different compositions of magma.agma. Magma is the term used to describe molten material within the Earth; in simple terms: molten rock. But the molten rock usually contains some suspended crystals or dissolved gases.