The Mineral arsenopyrite

Arsenopyrite Individual Crystals

Arsenopyrite is the most prevalent mineral containing the element arsenic. It forms very distinct crystals, which can be large and beautifully formed. Arsenopyrite sometimes tarnishes, forming a colorful iridescent layer.

Chemical Formula



Silver-white to steel-gray. Tarnishes dark gray, but occasionally also an iridescent pink and yellow.

Crystal System



5.5 - 6.5
Specific Gravity
5.9 - 6.2
2,1 - prismatic
Other ID Marks
1) Gives off a garlic odor when struck or heated.
2) Triboluminescent.

Crystal Habits

Arsenopyrite was previously thought to crystallize in the orthorhombic system, but recent analysis indicates a monoclinic symmetry. Occurs as distinct prismatic crystals, which are often twinned and triangular in shape. Twins may form interesting crosses and stars. Also occurs as elongated crystals, columnar, grainy, massive, as veins, and in compact crystal groups. Crystals are usually striated.

3D Crystal Atlas

Additional Information

Iron arsenic sulfide, sometimes with some cobalt
In Group
Sulfides; Simple Sulfides
Striking Features
Crystal habits, gives off garlic odor when struck
High temperature ore veins, pegmatites, and contact metamorphic rocks. Rarely in igneous basalt rocks.
Rock Type
Igneous, Sedimentary, Metamorphic


 -   Cobalt-rich variety of Arsenopyrite, in which the cobalt may replace as much as 12 percent of the iron. Found in Franconia, New Hampshire.
 -   Mineral almost identical to Arsenopyrite, but contains antimony in place of the arsenic. Its chemical formula is FeSbS. Gudmundite is very similar in physical properties to Arsenopyrite, and is sometimes wrongly classified as a variety of it, when in fact it is scientifically a separate mineral species. It is found in Gudmundstorp, Sala, Sweden, and Ilimaussaq, Greenland.


Arsenopyrite is an important ore of the element arsenic. It is also a minor ore of gold, as it contains traces of gold in some localities. Well-formed, lustrous Arsenopyrite crytals are important collector specimens.

Noteworthy Localities

Arsenopyrite can be found worldwide, but crystals of good quality are more limited. Excellent specimens of Arsenopyrite are found in Asia at the Yaogangxian Mine, Hunan Province, China; the Huanggang Mine, Inner Mongolia, China; and the Obira Mine on Kyushu Island, Japan.

Important European localities for Arsenopyrite include Panasqueira, Portugal; Freiberg, Saxony, Germany; Trepca, Kosovo (former Yugoslavia); and several of the ore deposits in the Cornwall area in England. In South America, fine Arsenopyrite crystals have come from Potosi, Bolivia; and the Pachapaqui District, Ancash Dept., Peru. Mexico also contains several notable occurrences, especially the Santa Eulalia district, Chihuahua; and Concepcion del Oro, Zacatecas.

In the U.S., Arsenopyrite localities include Mount Mica, Oxford Co., Maine; Roxbury, Litchfield Co., Connecticut; Lewis, Essex Co., New York; Franklin, Sussex Co., New Jersey; Leadville, Lake Co., Colorado; and the Cleveland mine, Stevens Co., Washington. Fine specimens were once found Carmel, Putnam Co., New York. The cobalt-rich variety, Danaite, comes from Franconia, Grafton Co., New Hampshire. In Canada, Arsenopyrite is found in the Cobalt area, Timiskaming District, Ontario; and in the Nickel Plate Mine, British Columbia.

Distingushing Similar Minerals

Pyrite, Marcasite, and Pyrrhotite - Occur in different crystals, more yellow in color.
Loellingite - Very hard to distinguish, but lacks the sulfur attributes of Arsenopyrite.
Cobaltite - Occurs in different crystals.


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