Black smoker vent in the High-Rise field, Endeavour segment, Juan de Fuca ridge. Handheld photo taken from inside Alvin submersible, June 2009. Metals and hydrogen sulfide combine to form dark sulfide minerals when hot fluids mix with seawater. Image courtesy of D. Butterfield, Univ. of Washington and J. Holden, Univ. Massachusetts Amherst.