Magnesiochromite is an oxide mineral belonging to the spinel group, typically found as an accessory mineral in ultramafic rocks. It appears as dark, opaque octahedra or granular masses that are often indistinguishable from chromite without chemical analysis. Collectors typically find it in peridotite or serpentinite environments, often associated with the breakdown of mantle-derived minerals.
Is this magnesiochromite?
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 magnesiochromite with a known reference. Magnesiochromite sits at Mohs 5.5-7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, massive, granular.
Often confused with
Magnesiochromite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Magnesiochromite leaves brown, Magnetite leaves black.
How to tell apart: Streak differs, so Magnesiochromite leaves brown, Franklinite leaves reddish brown to black.
Often found alongside magnesiochromite
Minerals reported to co-occur with magnesiochromite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgCr₂O₄
- Mohs hardness
- 5.5-7
- Density
- 4.39-4.67 g/cm³
- Colors
- Streak
- Brown
- Luster
- Metallic
- Transparency
- Opaque, transmits light through thin edges
- Crystal system
- Cubic
- Crystal habit
- Octahedral crystals, massive, granular
- Cleavage
- Parting on {111}, possible
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- An accessory mineral in ultramafic rocks, as dunites, serpentinites, kimberlites, lamproites, and komatiites
Where rockhounds find magnesiochromite
Classic worldwide localities
- Line Pit, Lancaster Co., Pennsylvania, USA
- Leucite Hills, Sweetwater Co., Wyoming, USA
- Tampadel and Groschau, Lower Silesia, Poland
- Dobřiš, and at Hamry, near Křemže, Czech Republic
- Ferdinandovo, Bulgaria
- Mt. Djeti, Togo
Field-hunting tip
Where it forms: An accessory mineral in ultramafic rocks, as dunites, serpentinites, kimberlites, lamproites, and komatiites. If you start seeing olivine, augite, magnetite in float, you are in the right ground. Typical habit: octahedral crystals, massive, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify magnesiochromite?+
Where is magnesiochromite found?+
What rocks look like magnesiochromite?+
What minerals are found with magnesiochromite?+
What kind of rock does magnesiochromite form in?+
What is magnesiochromite used for?+
Find magnesiochromite on the map
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