This mix of mimetite and calcite is from the Ojuela Mine in Mapimi, Durango, Mexico. There a over 115 different types of minerals in the mine including these two. Mimetite is an arsenate that contains the elements Pb, As, O and Cl. This piece consists of a goethite matrix that is partially topped with rhombic calcites that host euhedral barrel-like crystals of mimetite. It measures3 x 2 1/4 x 1 5/8 inches or 76 x 57 x 41 mm.