Tyrrellite is a very rare copper-iron-cobalt selenide mineral that typically forms as small, steel-pale bronze metallic grains. It is most famous for its occurrences in selenide-rich hydrothermal mineral assemblages, often found alongside clausthalite.
Is this tyrrellite?
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 tyrrellite with a known reference. Tyrrellite sits at Mohs ~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.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: bronze.
- 5Look at form & habitCrystal system: cubic. Typical habit: granular.
Often confused with
Tyrrellite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Tyrrellite leaves black, Clausthalite leaves grayish black.
How to tell apart: Tyrrellite is noticeably harder (Mohs ~3.5 vs. 2.7); streak differs, so Tyrrellite leaves black, Berzelianite leaves shining.
How to tell apart: Linnaeite is the harder of the two (Mohs 4.5-5.5 vs. ~3.5); streak differs, so Tyrrellite leaves black, Linnaeite leaves grayish black.
Often found alongside tyrrellite
Minerals reported to co-occur with tyrrellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu(Co,Ni)₂Se₄
- Mohs hardness
- ~3.5
- Density
- 6.6 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Granular
- Cleavage
- {001}, poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- With other selenides, as the youngest hydrothermal replacements and open space fillings in sheared Precambrian rocks, which also contain uraninite deposits (Goldfields district, Canada)
Where rockhounds find tyrrellite
Classic worldwide localities
- Western part of the Eagle claims, and also at the head of Ato Bay, Beaverlodge Lake, Goldfields district, Saskatchewan (type locality), Canada
- Bukov, near Tisnova, on Koksín Hill, near Mitov, and in the Petrovice uranium deposit, near Ždǎr, Czech Republic
- Hope’s Nose, Torquay, Devon, England
- Tuminico, Sierra de Cacho, and at Los Llantenes, La Rioja Province, Argentina
Field-hunting tip
Where it forms: With other selenides, as the youngest hydrothermal replacements and open space fillings in sheared Precambrian rocks, which also contain uraninite deposits (Goldfields district, Canada). If you start seeing umangite, klockmannite, clausthalite in float, you are in the right ground. Typical habit: granular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find tyrrellite on the map
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