(named for the Scottish mineralogist R. Jameson, 1774-1854), a mineral from the sulfide group. Its chemical composition is Pb₄FeSb₆S₁₄; Cu, Ag, and Zn are present as impurities. Jamesonite has a complex, chain-type structure and crystallizes in the monoclinic system. It forms filiform-acicular, capillary, felted, and granular aggregates, and, more rarely, fine acicular or fibrous lead-gray crystals with a metallic luster. Jamesonite is brittle. Its hardness on the mineralogical scale is 2-3, and its density measures 5,500-6,000 kg/m³. It is found in ores of lead-zinc hydrothermal deposits.