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Algodonite

Discovered in 1857; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Cu₆As

Copper Arsenide

Molecular Weight:

456.20 gm

Composition:

Copper

83.58 %

Cu

Arsenic

16.42 %

As

100.00 %

Classification

Mineral Classification:

Sulfides

Strunz 8th Ed. ID:

2/A.01-10

Nickel-Strunz 10th Ed. ID:

2.AA.10a

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
A : Alloys
A : Alloys of metalloids with Cu, Ag, Au

Related to:

n/a

Varieties:

Argentoalgodonite

Synonyms:

Algadonite, Whitneyite

Crystal Data

Crystallography:

Hexagonal - Dihexagonal Dipyramidal

Crystal Habit:

As incrustations of minute highly distorted crystals; commonly massive and granular. 

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

4.0; Vickers: VHN₁₀₀= 245 - 302 kg/mm²

Density:

8.38 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Steel-gray to silver-white, tarnishes dull on exposure; in polished section, bright cream-white.

Transparency:

Opaque

Luster:

Bright Metallic

Refractive Index:

R1–R2: (400) 51.5–49.3, (420) 52.3–50.5, (440) 52.8–52.4, (460) 53.4–54.6, (480) 54.2–56.4, (500) 55.7–58.4, (520) 57.5–60.5, (540) 58.9–62.3, (560) 60.0–63.8, (580) 60.8–64.8, (600) 61.1–65.5, (620) 61.6–66.1, (640) 61.9–66.5, (660) 62.3–66.7, (680) 62.8–66.9, (700) 63.4–67.1

Birefringence:

None (opaque)

Dispersion:

n/a

Pleochroism:

n/a

Anisotropism:

Weak; color in reflected light: bright cream-white

Occurances

Geological Setting:

Uncommon in hydrothermal deposits, intimately associated with other copper arsenides.

Common Associations:

Copper (typically arsenian), Silver, Domeykite, Koutekite

Common Impurities:

Ag

Type Locality:

Los Algodones Mine, Los Algodones district, El Arrayan, La Serena, Elqui Province, Coquimbo Region, Chile

Year Discovered:

1857

View mineral photos:

Algodonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Algodonite is a copper arsenide mineral that is frequently associated with Domeykite and other copper arsenides and often found as a mixture of these minerals, creating Mohawkite. Mohawkite is a mixture of Algodonite, Domeykite, arsenic-rich Copper and may also contain other minerals such as silver, cobalt, nickel or iron. Mohawkite is not considered a valid mineral species because it is a mixture, or alloy-like coumpound. Mohawkite is often mixed with Quartz crystal clusters as seen in the picture at the top of this page. This makes for a very attractive cabochon with bright, metallic, brassy Mohawkite and bright white Quartz. Cabochons of Algodonite, Domeykite and Mohawkite are bright and attractive with metallic luster but will tarnish quickly and turn a drab brown and lose their luster. They must be coated with lacquer or other protective coating to prevent tarnishing. Faceted gems are beautiful when cut and polished to a high luster but are very rarely available. Algodonite and Domeykite are heat sensitive, and care must be exercised when cutting.

Algodonite was named in 1859 by F. Field for the discovery locality at the Los Algodones Mine, Los Algodones district, El Arrayan, La Serena, Elqui Province, Coquimbo Region, Chile. Mohawkite is named after the originally reported, and only, locality at the Mohawk Mine, Mohawk, Keweenaw County, Michigan, USA.

Algodonite distribution: in Chile, at the Type Locality of the Los Algodones Mine, near Coquimbo, and the Cerro de las Seguas, Rancagua, O’Higgins Province. At Corocoro, Bolivia. In the Kokito II mine, Neuquén Province, Argentina. In the USA, in Michigan, from Keweenaw County, at the Mohawk, Pewabic, Seneca, Ahmeek, and Champion mines, and at Painesdale, Houghton County, also from Baraga County; in Colorado, from the Cashin mine, Montrose County. At Långban, Värmland, Sweden. In France, from the Roua copper mines, about 50 km north of Nice, Alpes-Maritimes. At Tsumeb, Namibia. In the Talmessi mine, 35 km west of Anarak, Iran.

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