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 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Magnesiochromite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Magnesiochromite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-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 — Magnesiochromite leaves brown, Chromite leaves dark brown.
How to tell apart: Streak differs — Magnesiochromite leaves brown, Magnetite leaves black; luster reads submetallic on Magnesiochromite and metallic on Magnetite.
How to tell apart: Streak differs — Magnesiochromite leaves brown, Franklinite leaves reddish-brown; luster reads submetallic on Magnesiochromite and metallic on Franklinite.
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
- Density
- 4.1-4.5 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Octahedral Crystals, Massive, Granular
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Ultramafic Igneous Rocks, Serpentinite
- Typical price
- $15-60 thumbnail
Where rockhounds find magnesiochromite
Classic worldwide localities
- Bushveld Complex, South Africa
- Great Dyke, Zimbabwe
- Oman Ophiolite, Oman
- Ural Mountains, Russia
Field-hunting tip
Look in ultramafic igneous rocks, serpentinite country — that is the host setting where magnesiochromite typically forms. If you start seeing olivine, enstatite, serpentine in float, you are in the right ground. Field specimens usually show a octahedral crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find magnesiochromite on the map
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