magma is mainly composed of
Magma (from Greek Î¼Î¬Î³Î¼Î±, thick unguent) is a mixture of molten or semi-molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals, dissolved gas and sometimes gas bubbles.nvironments of magma formation and compositions are commonly correlated. Environments include subduction zones, continental rift zones, mid-ocean ridges and hotspots. Despite being found in such widespread locales, the bulk of the Earth's crust and mantle is not molten.