Hercynite is a member of the spinel group characterized by its deep black to dark green color and high hardness. It is typically found in high-grade metamorphic rocks resulting from the contact metamorphism of aluminous sediments. Collectors should look for its sharp octahedral habit, though it is frequently found as massive, irregular grains.
Is this hercynite?
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 hercynite with a known reference. Hercynite 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. Hercynite leaves a dark green streak.
- 3Read the lusterHold the specimen under a strong light. Hercynite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, dark green.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, massive, granular.
Often confused with
Hercynite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Hercynite is noticeably harder (Mohs 7.5-8 vs. 5.5-6.5); streak differs — Hercynite leaves dark green, Magnetite leaves black; luster reads vitreous on Hercynite and metallic on Magnetite.
How to tell apart: Hercynite is noticeably harder (Mohs 7.5-8 vs. 5.5); streak differs — Hercynite leaves dark green, Chromite leaves dark brown; luster reads vitreous on Hercynite and submetallic on Chromite.
How to tell apart: Streak differs — Hercynite leaves dark green, Spinel leaves white.
Often found alongside hercynite
Minerals reported to co-occur with hercynite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeAl₂O₄
- Mohs hardness
- 7.5-8
- Density
- 4.39-4.41 g/cm³
- Colors
- Streak
- Dark Green
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Octahedral Crystals, Massive, Granular
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Metamorphic Rocks Like Schist and Gneiss, Sometimes in Igneous Rocks
- Typical price
- $10-50 per small specimen
Where rockhounds find hercynite
Classic worldwide localities
- Harz Mountains, Germany
- New York, USA
- Madagascar
- Sri Lanka
- Australia
Field-hunting tip
Look in metamorphic rocks like schist and gneiss, sometimes in igneous rocks country — that is the host setting where hercynite typically forms. If you start seeing corundum, sillimanite, staurolite 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 hercynite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
