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, so Freboldite leaves black, Galena leaves lead-gray.
How to tell apart: Streak differs, so 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, 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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