Witzkeite: a new rare nitrate-sulphate mineral from a guano deposit at Punta de Lobos, Chile - Nestola, Fabrizio; Cámara, Fernando; Chukanov, Nikita V; Atencio, Daniel; Coutinho, José Moacyr Vianna; Contreira Filho, Reynaldo R; Färber, Gunnar (American Mineralogist, 2012)