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. Eucairite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Eucairite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: lead-gray, silver-white.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: massive, granular, or as interstitial grains in ores.
Often confused with
Eucairite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Chalcopyrite is the harder of the two (Mohs 3.5-4 vs. 2.5); streak differs — Eucairite leaves black, Chalcopyrite leaves greenish-black.
How to tell apart: Streak differs — Eucairite leaves black, Clausthalite leaves gray-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
- 7.5 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Massive, Granular, Or as Interstitial Grains in Ores
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Selenium-rich Veins
- Typical price
- $50-300 per small specimen
Where rockhounds find eucairite
Classic worldwide localities
- Skrikerum, Sweden
- Tumiñico mine, Argentina
- Kloch, Austria
- Coquimbo, Chile
Field-hunting tip
Look in hydrothermal selenium-rich veins country — that is the host setting where eucairite typically forms. If you start seeing clausthalite, berzelianite, umangite in float, you are in the right ground. Field specimens usually show a massive, granular, or as interstitial grains in ores habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find eucairite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
