Domeykite is a metallic copper arsenide typically found as massive or botryoidal aggregates that tarnish to a dull yellowish color over time. It is easily identified by its high density and metallic luster, often occurring alongside native copper in hydrothermal veins. Collectors should handle this mineral with caution due to its arsenic content.
Is this domeykite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch domeykite with a known reference. Domeykite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: tin white, gray, yellow brown, silver white.
- 5Look at form & habitCrystal system: cubic. Typical habit: botryoidal, massive, reniform.
Often confused with
Domeykite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Domeykite leaves black gray, Algodonite leaves white; luster reads metallic on Domeykite and bright metallic on Algodonite.
How to tell apart: Streak differs, so Domeykite leaves black gray, Arsenic leaves tin-white; luster reads metallic on Domeykite and nearly metallic on Arsenic.
How to tell apart: Nickeline is the harder of the two (Mohs 5-5.5 vs. 3-3.5); streak differs, so Domeykite leaves black gray, Nickeline leaves pale brownish black.
Often found alongside domeykite
Minerals reported to co-occur with domeykite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃As
- Mohs hardness
- 3-3.5
- Density
- 7.2-7.9 g/cm³
- Streak
- Black gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Botryoidal, massive, reniform
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Ore of copper
- Host rock
- Of hydrothermal origin
Where rockhounds find domeykite
Classic worldwide localities
- Mohawk and Ahmeek mines, Keweenaw Co., and in the Sheldon-Columbia mine, Portage Lake, Houghton Co., Michigan, USA
- Cashin mine, Montrose Co., Colorado, USA
- Franklin, Sussex Co., New Jersey, USA
- Algodones silver mine, near Coquimbo (type locality) and at San Antonio and Chañarcillo, near Copiapó, Atacama, Chile
- Corocoro, Bolivia
- Cerro de Paracatas, Tlachapa, Guerrero, Mexico
Field-hunting tip
Where it forms: Of hydrothermal origin. If you start seeing copper, silver, algodonite in float, you are in the right ground. Typical habit: botryoidal, massive, reniform. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify domeykite?+
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Is domeykite safe to handle?+
What rocks look like domeykite?+
What minerals are found with domeykite?+
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Find domeykite on the map
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