Freboldite is a rare cobalt selenide mineral that typically occurs as massive, metallic-gray aggregates. It is most commonly identified in hydrothermal vein environments associated with other rare selenides and uranium minerals.
Is this freboldite?
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 freboldite with a known reference. Freboldite sits at Mohs 3.5-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Freboldite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Freboldite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: dark gray, grayish white.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: massive, anhedral grains.
Often confused with
Freboldite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Freboldite is noticeably harder (Mohs 3.5-4 vs. 2.5); streak differs — Freboldite leaves black, Galena leaves lead-gray.
How to tell apart: Streak differs — Freboldite leaves black, Clausthalite leaves gray-black.
Often found alongside freboldite
Minerals reported to co-occur with freboldite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CoSe
- Mohs hardness
- 3.5-4
- Density
- 6.14 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Massive, Anhedral Grains
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Hydrothermal Selenide Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find freboldite
Classic worldwide localities
- Frebold Valley, Argentina
- Hope Bay, Canada
- Clausthal-Zellerfeld, Germany
Field-hunting tip
Look in hydrothermal selenide deposits country — that is the host setting where freboldite typically forms. If you start seeing clausthalite, berzelianite, uraninite in float, you are in the right ground. Field specimens usually show a massive, anhedral grains habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find freboldite on the map
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