* [https://books.google.es/books?id=yb9xTj72vNAC&redir_esc=y&hl=es Krebs, Robert E. (2006). The history and use of our earth's chemical elements: a reference guide. Greenwood Publishing Group. p. 80. ISBN 0-313-33438-2] | * [https://books.google.es/books?id=yb9xTj72vNAC&redir_esc=y&hl=es Krebs, Robert E. (2006). The history and use of our earth's chemical elements: a reference guide. Greenwood Publishing Group. p. 80. ISBN 0-313-33438-2] |