molten

Molten is the adjective used for a substance that has been heated beyond its melting point and exists as a liquid that can flow. The term is most often applied to metals in metallurgy, but it also describes silicate melts such as lava and glass, as well as other materials that turn liquid when heated. In the molten state, a substance loses its fixed crystal structure and assumes the shape of its container.

Melting occurs at a characteristic temperature known as the melting point. Heat input at or above this temperature provides latent heat of fusion, enabling the solid to become a liquid. Above the melting point, further heating generally lowers viscosity, so molten metals and silicates flow more readily; however, viscosity varies widely by material and impurities. The molten state is typically temporary, ending when the liquid cools and solidifies.

Natural and industrial contexts are both central to the concept. In nature, molten material exists as magma within Earth's interior and as lava on the surface during volcanic activity. In industry, molten materials are used in metal casting, alloy production, welding, and glassmaking. Processing often requires specialized furnaces, crucibles, and refractory linings, as well as controlled atmospheres to minimize oxidation and contamination.

Safety and handling considerations are important due to high temperatures, dangerous fumes, and reactions with air or moisture. Protective equipment and robust containment systems are standard in operations involving molten materials. The term “molten” thus denotes a dynamic liquid state integral to both natural processes and a wide range of industrial applications.