Kusachiite is a very rare copper bismuth oxide mineral first identified in the Kusachi mine in Japan. It typically occurs as tiny, dark-colored, tabular crystals within metasomatized limestone skarn deposits.
Is this kusachiite?
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 kusachiite with a known reference. Kusachiite sits at Mohs 4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: crystalline, globular, prismatic.
Often confused with
Kusachiite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Kusachiite is noticeably harder (Mohs 4.5 vs. 3.5).
How to tell apart: Streak differs, so Kusachiite leaves black, Bismite leaves gray to yellow; luster reads metallic on Kusachiite and subadamantine to dull, earthy on Bismite.
Often found alongside kusachiite
Minerals reported to co-occur with kusachiite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuBi₂O₄
- Mohs hardness
- 4.5
- Density
- 8.5 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Crystalline, globular, prismatic
- Cleavage
- {110}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- On calcite crystals in a calcite vein between gehlenite-spurrite skarn and limestone; thought to be of low-temperature hydrothermal origin
Where rockhounds find kusachiite
Classic worldwide localities
- Fuka, near Bicchu, Okayama Prefecture, Japan
Field-hunting tip
Where it forms: On calcite crystals in a calcite vein between gehlenite-spurrite skarn and limestone; thought to be of low-temperature hydrothermal origin. If you start seeing henmilite, sillénite, bakerite in float, you are in the right ground. Typical habit: crystalline, globular, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kusachiite?+
Where is kusachiite found?+
Is kusachiite safe to handle?+
What rocks look like kusachiite?+
What minerals are found with kusachiite?+
What kind of rock does kusachiite form in?+
What is kusachiite used for?+
Find kusachiite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
