Decagonite is a remarkable naturally occurring quasicrystal that exhibits forbidden icosahedral symmetry. It is found exclusively as microscopic inclusions within the Khatyrka meteorite and is characterized by its unique aluminum-nickel-iron composition.
Is this decagonite?
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 decagonite with a known reference. Decagonite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Decagonite leaves a gray streak.
- 3Read the lusterHold the specimen under a strong light. Decagonite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: silver, metallic gray.
- 5Look at form & habitCrystal system: icosahedral. Typical habit: anhedral grains.
Often confused with
Decagonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Decagonite leaves gray, Pyrite leaves greenish-black to brownish-black.
How to tell apart: Decagonite is noticeably harder (Mohs 6 vs. 3.5-4); streak differs, so Decagonite leaves gray, Pentlandite leaves light bronze-brown.
Often found alongside decagonite
Minerals reported to co-occur with decagonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₇₁Ni₂₄Fe₄
- Mohs hardness
- 6
- Density
- 6.05 g/cm³
- Colors
- Streak
- Gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Icosahedral
- Crystal habit
- Anhedral Grains
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- CV3 Carbonaceous Chondrite Meteorites
- Typical price
- n/a (extremely rare meteorite inclusion)
Where rockhounds find decagonite
Classic worldwide localities
- Khatyrka meteorite
- Chukotka Autonomous Okrug, Russia
Field-hunting tip
Look in cv3 carbonaceous chondrite meteorites country, the host setting where decagonite typically forms. If you start seeing stishovite, spinel, diopside in float, you are in the right ground. Field specimens usually show a anhedral grains habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find decagonite on the map
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