Gahnite is a zinc-rich member of the spinel group, frequently identified by its distinct octahedral habit and high specific gravity. It is commonly found in metamorphic environments and zinc-bearing ore deposits, often appearing as dark, sub-metallic to vitreous crystals embedded in host rocks.
Is this gahnite?
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 gahnite with a known reference. Gahnite 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. Gahnite leaves a gray streak.
- 3Read the lusterHold the specimen under a strong light. Gahnite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark green, blue-green, yellow, brown, black.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, often with rounded edges or twins.
Often confused with
Gahnite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Gahnite leaves gray, Spinel leaves white.
How to tell apart: Gahnite is noticeably harder (Mohs 7.5-8 vs. 5.5-6.5); streak differs — Gahnite leaves gray, Magnetite leaves black; luster reads vitreous on Gahnite and metallic on Magnetite.
How to tell apart: Gahnite is noticeably harder (Mohs 7.5-8 vs. 5.5); streak differs — Gahnite leaves gray, Chromite leaves dark brown; luster reads vitreous on Gahnite and submetallic on Chromite.
Often found alongside gahnite
Minerals reported to co-occur with gahnite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- ZnAl₂O₄
- Mohs hardness
- 7.5-8
- Density
- 4.4-4.6 g/cm³
- Streak
- Gray
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Octahedral Crystals, Often with Rounded Edges or Twins
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Indicator Mineral
- Host rock
- Metamorphic Rocks Like Skarns, Pegmatites, And Zinc-rich Ore Bodies
- Typical price
- $20-200 depending on crystal size and perfection
Where rockhounds find gahnite
Classic worldwide localities
- Falun, Sweden
- Franklin, New Jersey, USA
- Broken Hill, Australia
- Minas Gerais, Brazil
- Madagascar
Field-hunting tip
Look in metamorphic rocks like skarns, pegmatites, and zinc-rich ore bodies country — that is the host setting where gahnite typically forms. If you start seeing sphalerite, garnet, sillimanite in float, you are in the right ground. Field specimens usually show a octahedral crystals, often with rounded edges or twins habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find gahnite on the map
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