Ferropargasite has been synthesized and its stability relations investigated. From most to least oxidized, assemblages produced on decomposition are magnetite, plagioclase, andraditic garnet plus fluid; magnetite, plagioclase, garnet, hedenbergitic pyroxene, nepheline plus fluid; and hercynite, plagioclase, fayalite, hedenbergitic pyroxene, nepheline plus fluid. Principal effects caused by substituting Fe for Mg are lowering the high temperature stability limit at 1 kb fluid pressure from 1040 degrees C to 835 degrees C, and strong dependence of the ferropargasite stability field boundary on oxygen fugacity. Addition of silica lowers the upper thermal stability limit at low relative oxygen fugacities by 250 degrees C or more for fluid pressures of 2 kb. At high relative oxygen fugacities, addition of silica results in an amphibole whose upper stability limit is raised nearly 75 degrees C.