Martite is a classic pseudomorph where hematite has replaced magnetite, preserving the original octahedral crystal shape of the magnetite. Collectors look for sharp, metallic-black octahedrons that leave a telltale reddish-brown streak rather than the black streak of its parent magnetite.
Is this martite?
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 martite with a known reference. Martite sits at Mohs 5.5-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Martite leaves a reddish brown streak.
- 3Read the lusterHold the specimen under a strong light. Martite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black, dark gray.
- 5Look at form & habitCrystal system: trigonal. Typical habit: pseudomorphous octahedral crystals.
Often confused with
Martite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside martite
Minerals reported to co-occur with martite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂O₃
- Mohs hardness
- 5.5-6.5
- Density
- 5.2-5.3 g/cm³
- Streak
- Reddish Brown
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Pseudomorphous Octahedral Crystals
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Educational
- Host rock
- Hydrothermal Veins, Contact Metamorphic Rocks
- Typical price
- $5-50 for typical specimens
Where rockhounds find martite
1 mapped spotsClassic worldwide localities
- Minas Gerais, Brazil
- Marquette Range, Michigan, USA
- Elba, Italy
- Kiruna, Sweden
Field-hunting tip
Look in hydrothermal veins, contact metamorphic rocks country, the host setting where martite typically forms. If you start seeing magnetite, hematite, quartz in float, you are in the right ground. Field specimens usually show a pseudomorphous octahedral crystals habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New York. Start trip planning there.
Common questions
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Find martite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
