Hydrothermal vents are formed on oceanic spreading ridges (where two tectonic plates move away from each other) or subduction zones (where two tectonic plates collide). They are formed when seawater infiltrates down through cracks in the ocean crusts. The near freezing sea water is heated by hot magma and resurfaces to form vents. The vents emit jets of particle laden fluid, which solidify as they cool, forming chimney-like structures. There are two different types of vents: black smokers and white smokers. Black smokers are chimneys formed from deposits of iron sulfide, which is black. White smokers are chimneys formed from deposits of barium, calcium and silicon, which are white. The vents are surrounded by unique communities of organisms with specific adaptations, depending on the vents to convert minerals and other chemicals into energy in a process called chemosynthesis. Hydrothermal vents are of specific interest for deep-sea mining industries. The chimneys are an accumulation of valuable minerals like zinc, nickel and copper (see definition for key DSM metals). Mining the vents wipes out the entire living community, and it is unclear if these vents can recover. Like most benthic communities (see definition for benthic flora and fauna), scientists know very little about hydrothermal vents, so the extent of the destruction is not entirely known. Furthermore, the vents contain toxic chemicals like lead and arsenic that could spill in the mining process, potentially causing extensive harm to the surrounding ecosystems.