This selenite is from Santa Eulalia in the Mun. de Aquiles Serdan, Chihuahua, Mexico. This district encompasses a large area that contains over a dozen mines. Mining activities are primarily for the extraction of silver and other metals. There a over 150 different types of minerals in the district including selenite. It is a sulfate that contains the elements Ca, S, H and O. This specimen has a thin goethite matrix that is covered on the display side with fibrous elongated selenite crystals including a large “rams horn” formation. This piece measures 3 x 2 1/2 x 1 1/8 inches or 76 x 57 x 28 mm.