Algodonite is a rare copper arsenide mineral that typically forms as massive or granular aggregates with a silvery-white metallic luster. It is most famous for its occurrences in the native copper deposits of the Keweenaw Peninsula in Michigan, where it is often found intergrown with domeykite and native copper.
Is this algodonite?
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 algodonite with a known reference. Algodonite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: bright metallic.
- 4Match the color rangeCompare against the expected color range: silver white, gray, steel gray, tarnishes dull bronze.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: massive, tarnishes.
Often confused with
Algodonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Algodonite leaves white, Domeykite leaves black gray; luster reads bright metallic on Algodonite and metallic on Domeykite.
How to tell apart: Streak differs, so Algodonite leaves white, Koutekite leaves black; luster reads bright metallic on Algodonite and metallic on Koutekite.
How to tell apart: Algodonite is noticeably harder (Mohs 4 vs. 2.5-3); streak differs, so Algodonite leaves white, Silver leaves silver-white; luster reads bright metallic on Algodonite and metallic on Silver.
Often found alongside algodonite
Minerals reported to co-occur with algodonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₁.₇₁As₀.₂₉
- Mohs hardness
- 4
- Density
- 8.38 g/cm³
- Colors
- Streak
- White
- Luster
- Bright metallic
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Massive, tarnishes
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Ore
- Host rock
- Uncommon in hydrothermal deposits, intimately associated with other copper arsenides
Where rockhounds find algodonite
Classic worldwide localities
- Keweenaw Co., at the Mohawk, Pewabic, Seneca, Ahmeek, and Champion mines, and at Painesdale, Houghton Co., also from Baraga Co., Michigan, USA
- Cashin mine, Montrose Co., Colorado, USA
- Algodones silver mine, near Coquimbo (type locality), and the Cerro de las Seguas, Rancagua, O’Higgins Province, Chile
- Corocoro, Bolivia
- Kokito II mine, Neuquén Province, Argentina
- Långban, Värmland, Sweden
Field-hunting tip
Where it forms: Uncommon in hydrothermal deposits, intimately associated with other copper arsenides. If you start seeing copper, silver, domeykite in float, you are in the right ground. Typical habit: massive, tarnishes. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify algodonite?+
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Find algodonite on the map
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