Emmonsite, also known as durdenite, is a mineral with the formula:
Fe₂(TeO₃)₃·2(H₂O).

Emmonsite forms triclinic crystals. It is of a yellowish-green color, with a vitreous lustre, and a hardness of 5 on the Moh scale. It was named for the American geologist, Samuel Franklin Emmons

Samuel Franklin Emmons

Samuel Franklin Emmons was an American Geologist. He was born in Boston, Massachusetts. He graduated from Harvard University in 1861 and studied at the Ecole des Mines in Paris, France from 1862–1864 and at the Frieberg mining school from 1865-1865. In May 1867, he was appointed assistant...

, (1841–1911), of the United States Geological Survey

United States Geological Survey

The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...

. Emmons discovered it in 1885, and he named the mineral durdenite.

It is categorized variously as an oxide

Oxide

An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....

, a tellurite

Tellurite

Tellurite is a rare oxide mineral composed of tellurium dioxide .It occurs as prismatic to acicular transparent yellow to white orthorhombic crystals. It occurs in the oxidation zone of mineral deposits in association with native tellurium, emmonsite and other tellurium minerals. Its name comes...

, or a tellurate

Tellurate

The tellurate ion is TeO42− or TeO66−.Unlike sulfate, tellurate is a somewhat good oxidizer; it can be reduced to tellurite or tellurium....

.

Emmonsite is found, often with quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 or cerussite

Cerussite

Cerussite is a mineral consisting of lead carbonate , and an important ore of lead. The name is from the Latin cerussa, white lead. Cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832 F. S. Beudant applied the name cruse to the mineral, whilst the present form, cerussite, is due to...

, in the Tombstone, Arizona

Tombstone, Arizona

Tombstone is a city in Cochise County, Arizona, United States, founded in 1879 by Ed Schieffelin in what was then Pima County, Arizona Territory. It was one of the last wide-open frontier boomtowns in the American Old West. From about 1877 to 1890, the town's mines produced USD $40 to $85 million...

 area. This rare mineral has been found, in 2010, in Sonora, Mexico. It is also associated with native tellurium, tellurite

Tellurite

Tellurite is a rare oxide mineral composed of tellurium dioxide .It occurs as prismatic to acicular transparent yellow to white orthorhombic crystals. It occurs in the oxidation zone of mineral deposits in association with native tellurium, emmonsite and other tellurium minerals. Its name comes...

, gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

, pyrite

Pyrite

The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...

and a variety of rare tellurium minerals.