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Yellow-green earthy massive chapmanite
Category Phyllosilicate
(repeating unit)
Strunz classification 09.ED.25
Crystal system Monoclinic-domatic
Color Yellow, green, olive green
Crystal habit Earthy massive; granular
Cleavage Poor
Fracture Conchoidal to irregular
Mohs scale hardness 2.5
Luster Nonmetallic, dull to adamantine
Streak Yellowish green
Specific gravity 3.69-3.75
Refractive index nα=1.850 nβ=1.950 nγ=1.960
Pleochroism None

Chapmanite is a rare silicate mineral 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. Chemically, it is an iron antimony silicate, closely related to bismutoferrite, and may contain aluminium impurities. It is closely associated with silver mines, most notably the Keeley mine in Ontario, Canada, found in quartz veinlets containing graphite 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.