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A mixture of molten rocks and gases found under the surface of the Earth or other planets. Magma is heated by heat from within the Earth and is found at varying depths below the surface. In places where the Earth’s crust is thinner, magma may rise closer to the surface. Its proximity can then manifest itself in a variety of geothermal phenomena such as hot springs, geysers, or fumaroles. Magma can have a variety of compositions. Depending on the silica content, magma is divided into felsic (higher silica content, e.g., granite) and mafic (lower silica content, e.g., basalt). When a volcano erupts, magma can be poured out onto the Earth’s surface, and is then called lava.