These mimetite crystals are 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. Calcite is a carbonate containing the elements Ca, C, and O. This piece consists of a mound-like formation of rhombohedral calcite crystals that hosts dozens of euhedral mimetite crystals. It measures 2 x 1 5/8 x 1 3/8 inches or 50 x 41 x 35 mm.