Chapmanite is a rare silicate belonging to the nesosilicate group, discovered in 1924, and named in honour of the late Edward John Chapman (1821–1904), a geology professor at the University of Toronto antimony, and may contain aluminium impurities. It is closely associated with silver , Canada in gneiss. It takes the form of a powdery, yellow-green, semitransparent solid, and leaves a streak of the same color. Early German texts have referred to the mineral as antimon-hypochlorite.
It was recently rediscovered in the southern hemisphere at the abandoned Argent lead mine in Bushveld series rocks of South Africa.