Madocite is a mineral with a general formula of Pb₁₇(Sb,As)₁₆S₄₁. Madocite was named for the locality of discovery, Madoc, Ontario, Canada. It is found in the marbles of the Precambrian Grenville Limestone. It is orthorhombic (rectangular prism with a rectangular base) and in the point group mm2. Its crystals are elongated and striated along (001) to a size of 1.5 mm.