Magma

Magma, molten material formed in the upper mantle, or crust, of the earth, composed of a mixture of various complex silicates in which are dissolved various gaseous materials, including water. On cooling, magma forms igneous rocks, though any gaseous constituents are usually lost during the solidification. Magma extruded to the surface forms lava. The term is loosely applied to other fluid substances in the earth's crust.