Eucairite is a rare silver-copper selenide that typically occurs as lead-gray metallic masses in hydrothermal ore deposits. It is best identified by its association with other rare selenide minerals in specific localities such as the type locality at Skrikerum, Sweden. Collectors should handle specimens with care due to the presence of selenium.
Is this eucairite?
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 eucairite with a known reference. Eucairite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: shining.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: bronze, gray, silver white, tin white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: aggregates.
Often confused with
Eucairite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Eucairite leaves shining, Acanthite leaves black.
How to tell apart: Chalcopyrite is the harder of the two (Mohs 3.5-4 vs. 2.5); streak differs, so Eucairite leaves shining, Chalcopyrite leaves greenish black.
How to tell apart: Streak differs, so Eucairite leaves shining, Clausthalite leaves grayish black.
Often found alongside eucairite
Minerals reported to co-occur with eucairite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AgCuSe
- Mohs hardness
- 2.5
- Density
- 7.6-7.8 g/cm³
- Streak
- Shining
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Aggregates
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Widely distributed in selenium deposits of hydrothermal origin; locally abundant with other selenides
Where rockhounds find eucairite
Classic worldwide localities
- Cougar mine, Slick Rock district, San Miguel Co., Colorado, USA
- Tryserum, Kalmar (type locality), Sweden
- Frederik VII’s mine, near Julianehåb, southern Greenland
- Harz Mountains, from the Trogtal quarry, near Lautenthal, and at Lerbach, Germany
- Kletno, Poland
- Bukov, near Tisnova, Czech Republic
Field-hunting tip
Where it forms: Widely distributed in selenium deposits of hydrothermal origin; locally abundant with other selenides. If you start seeing berzelianite, weissite, crookesite in float, you are in the right ground. Typical habit: aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Is eucairite safe to handle?+
What rocks look like eucairite?+
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Find eucairite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
