Emmonsite, also known as durdenite, is an iron tellurite mineral with the formula: Fe2(TeO3)3·2(H2O). Emmonsite forms triclinic crystals. It is of a yellowish-green color, with a vitreous luster, and a hardness of 5 on the Moh scale. Emmonsite was first described in 1885 for an occurrence in the Tombstone District, Cochise County, Arizona. It was named for the American geologist, Samuel Franklin Emmons, (1841–1911), of the United States Geological Survey. Emmonsite is found, often with quartz or cerussite in the Tombstone, Arizona area. It is also associated with native tellurium, tellurite, native gold, pyrite, rodalquilarite, mackayite, sonoraite, cuzticite and eztlite.