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 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Kusachiite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Kusachiite typically shows a subadamantine luster.
- 4Match the color rangeCompare against the expected color range: black, dark brown.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: tabular crystals, aggregates.
Often confused with
Kusachiite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Kusachiite leaves brown, Tenorite leaves black; luster reads subadamantine on Kusachiite and metallic on Tenorite.
How to tell apart: Streak differs — Kusachiite leaves brown, Bismite leaves white; luster reads subadamantine on Kusachiite and adamantine 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
- 3-4
- Density
- 6.2 g/cm³
- Colors
- Streak
- Brown
- Luster
- Subadamantine
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Tabular Crystals, Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metasomatized Limestone
- Typical price
- $50-300 per specimen depending on size
Where rockhounds find kusachiite
Classic worldwide localities
- Kusachi mine, Gunma Prefecture, Japan
Field-hunting tip
Look in metasomatized limestone country — that is the host setting where kusachiite typically forms. If you start seeing kuselite, bismite, copper in float, you are in the right ground. Field specimens usually show a tabular crystals, aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kusachiite?+
Where is kusachiite found?+
How much is kusachiite worth?+
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.
