Janggunite is a rare manganese oxide mineral typically found as fibrous or radiating crusts within manganese-rich ore deposits. It is often identified by its dark brown streak and submetallic luster in specimens associated with rhodochrosite.
Is this janggunite?
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 janggunite with a known reference. Janggunite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brownish black to dark brown.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: colloform, dendritic, flakes.
Often confused with
Janggunite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Hausmannite is the harder of the two (Mohs 5.5 vs. 2-3); streak differs, so Janggunite leaves brownish black to dark brown, Hausmannite leaves dark reddish brown; luster reads dull on Janggunite and submetallic on Hausmannite.
How to tell apart: Psilomelane is the harder of the two (Mohs 5-6 vs. 2-3); luster reads dull on Janggunite and submetallic on Psilomelane.
How to tell apart: Streak differs, so Janggunite leaves brownish black to dark brown, Pyrolusite leaves black, bluish black; luster reads dull on Janggunite and metallic on Pyrolusite.
Often found alongside janggunite
Minerals reported to co-occur with janggunite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mn⁴⁺,Mn²⁺,Fe³⁺)₆O₈(OH)₆
- Mohs hardness
- 2-3
- Density
- 3.59 g/cm³
- Colors
- Streak
- Brownish black to dark brown
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Colloform, dendritic, flakes
- Cleavage
- One direction, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Formed at a late stage of oxidation in a cementation zone of a manganese deposit
Where rockhounds find janggunite
Classic worldwide localities
- Janggun mine, Bonghwa district, South Korea
Field-hunting tip
Where it forms: Formed at a late stage of oxidation in a cementation zone of a manganese deposit. If you start seeing nsutite, todorokite, calcite in float, you are in the right ground. Typical habit: colloform, dendritic, flakes. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify janggunite?+
Where is janggunite found?+
What rocks look like janggunite?+
What minerals are found with janggunite?+
What kind of rock does janggunite form in?+
What is janggunite used for?+
Find janggunite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
