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 submetallic luster.
- 4Match the color rangeCompare against the expected color range: dark brownish gray.
- 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, so Fukuchilite leaves black, Pyrite leaves greenish-black to brownish-black; luster reads submetallic on Fukuchilite and metallic on Pyrite.
How to tell apart: Streak differs, so Fukuchilite leaves black, Chalcopyrite leaves greenish-black; luster reads submetallic on Fukuchilite and metallic on Chalcopyrite.
How to tell apart: Streak differs, so Fukuchilite leaves black, Bornite leaves grayish black; luster reads submetallic on Fukuchilite and metallic on Bornite.
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
- Colors
- Streak
- Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Massive, Granular Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Sulfide Deposits
Where rockhounds find fukuchilite
Classic worldwide localities
- Fukuchi mine, Japan
- Bor copper mine, Serbia
Field-hunting tip
Look in hydrothermal sulfide deposits country, 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?+
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Is fukuchilite safe to handle?+
What rocks look like fukuchilite?+
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Find fukuchilite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
