Cochromite is an extremely rare member of the spinel group where cobalt is a dominant cation. It typically occurs as small, opaque, black octahedral grains within serpentinized ultramafic rock environments. Collectors often identify it by its specific association with cobalt-rich ores in hydrothermal veins.
Is this cochromite?
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 cochromite with a known reference. Cochromite sits at Mohs 7.5-8, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cochromite leaves a greenish gray streak.
- 3Read the lusterHold the specimen under a strong light. Cochromite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, massive.
Often confused with
Cochromite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Cochromite is noticeably harder (Mohs 7.5-8 vs. 5.5); streak differs, so Cochromite leaves greenish gray, Chromite leaves dark brown; luster reads metallic on Cochromite and submetallic on Chromite.
How to tell apart: Cochromite is noticeably harder (Mohs 7.5-8 vs. 5.5-6.5); streak differs, so Cochromite leaves greenish gray, Magnetite leaves black; luster reads metallic on Cochromite and metallic to submetallic to dull on Magnetite.
How to tell apart: Streak differs, so Cochromite leaves greenish gray, Spinel leaves white; luster reads metallic on Cochromite and vitreous on Spinel.
Often found alongside cochromite
Minerals reported to co-occur with cochromite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Co,Ni,Fe,Mn)(Cr,Al)₂O₄
- Mohs hardness
- 7.5-8
- Density
- 4.6-4.8 g/cm³
- Colors
- Streak
- Greenish Gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Octahedral Crystals, Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Ultramafic Rocks, Serpentinites
Where rockhounds find cochromite
Classic worldwide localities
- 40 km north of Kanchanaburi, Thailand
Field-hunting tip
Look in ultramafic rocks, serpentinites country, the host setting where cochromite typically forms. If you start seeing chromite, serpentine, cobaltite in float, you are in the right ground. Field specimens usually show a octahedral crystals, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cochromite?+
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Find cochromite on the map
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