岩浆是熔化的岩石，通常位于地表之下的岩浆房中。岩浆是一种复杂的高温硅酸盐溶液，是各种火成岩的前身。岩浆可以侵入邻近的地壳岩石或是冒出地表。

岩浆存在于650℃到1200℃的温度中。可低至650℃，高至1400℃。熔岩中含有1~8%的挥发性物质。 岩浆处于高压之中，有时会经由火山道（或译火山管、火山流口）以熔岩流或是以火山碎屑物的火山喷出物的形式冒出。 这些火山喷发的产物通常包括了从没到过地表的液体、结晶体及溶解气体等。岩浆会在地壳中各自分离的岩浆库内集结，不同地方的岩浆组成成份会稍有不同。

这些地方包括了隐没带、裂谷带、中洋脊或是地函热柱的热点之上。只有在地球的软流圈内的特定条件之下岩浆才会形成。

Magma (from Greek μάγμα, "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 and some natural satellites. Besides molten rock, magma may also contain suspended crystals, dissolved gas and sometimes gas bubbles. Magma often collects in magma chambers that may feed a volcano or solidify underground to form an intrusion. Magma is capable of intrusion into adjacent rocks (forming igneous dikes and sills), extrusion onto the surface as lava, and explosive ejection as tephra to form pyroclastic rock.