Black AgSO4, synthesized for the first time by a displacement reaction, differs considerably from anhydrous sulfates of its Group 11 congeners: it has a very small electronic band gap (ca. 0.2 eV) and an anomalously strong one‐dimensional antiferromagnetic ordering ( J≈10 meV per Ag), which persists up to the onset of its thermal decomposition at about 120 °C. Ag gray, O red, S yellow.