Calculated pH of the intersection point for Fe2+, Fe3(OH)8 and Fe(OH)3 mineral equilibria for compositions of various low temperature vent fluids vs. the actual measured pH of the vent fluid at the site based upon data presented in the literature. 1 Franklin Seamount (ref. 5), 2 Galapagos Rift (ref. 61), 3 Loihi Seamount (ref. 60), 4 Axial Seamount (ref. 47), 5 Kasuga Seamounts (ref. 61), 6 21N East Pacific Rise (ref. 62), 7 Guaymas Basin (ref. 62).