The study of volcanoes, lava, magma, and related geological, geophysical, and geochemical processes is known as volcanology (sometimes spelled vulcanology) (volcanism). The name volcanology comes from the Latin word Vulcan, which means "vulcanized." Vulcan was the deity of fire in ancient Rome. A volcanologist is a geologist who examines volcanoes' present and historic eruptions, as well as their eruptive activity and genesis. Volcanologists commonly visit volcanoes, particularly those that are active, to monitor eruptions and collect eruptive products such as tephra (ash or pumice), rock, and lava samples. Forecasting eruptions is a major subject of research; while there is now no accurate means to do so, predicting volcanoes, like predicting earthquakes, might save countless lives. Magma (molten rock) cools and crystallizes at volcanoes on the surface of the Earth or when the melted rock is still inside the crust, forming igneous rocks. Because of the high heat underneath, all magma forms in the lower crust or upper mantle. Depending on the magma from which they cooled, igneous rocks can have a wide range of compositions. They can also take on varied appearances depending on how cool they are. Extrusive and intrusive igneous rocks are the two main types.