Fukuchilite is a rare copper-iron sulfide mineral typically found as small inclusions within other sulfide minerals. It is best identified through polished section microscopy or X-ray diffraction, as it rarely forms distinct macroscopic crystals of its own.
Is this fukuchilite?
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 fukuchilite with a known reference. Fukuchilite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Fukuchilite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Fukuchilite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: brass-yellow, yellowish-white.
- 5Look at form & habitCrystal system: cubic. Typical habit: massive, granular aggregates.
Often confused with
Fukuchilite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Pyrite is the harder of the two (Mohs 6-6.5 vs. 3-4); streak differs — Fukuchilite leaves black, Pyrite leaves greenish-black to brownish-black.
How to tell apart: Streak differs — Fukuchilite leaves black, Chalcopyrite leaves greenish-black.
How to tell apart: Streak differs — Fukuchilite leaves black, Bornite leaves greyish black.
Often found alongside fukuchilite
Minerals reported to co-occur with fukuchilite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃FeS₈
- Mohs hardness
- 3-4
- Density
- 4.6-4.8 g/cm³
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Massive, Granular Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Sulfide Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find fukuchilite
Classic worldwide localities
- Fukuchi mine, Japan
- Bor copper mine, Serbia
Field-hunting tip
Look in hydrothermal sulfide deposits country — that is the host setting where fukuchilite typically forms. If you start seeing pyrite, chalcopyrite, bornite in float, you are in the right ground. Field specimens usually show a massive, granular aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fukuchilite?+
Where is fukuchilite found?+
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Find fukuchilite on the map
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