Nagashimalite is an extremely rare barium vanadium silicate mineral typically found in metamorphosed manganese deposits in Japan. It usually occurs as small, dark brown to black tabular crystals or granular aggregates, often requiring microscopic examination for positive identification.

Hardness

Mohs

Luster

Submetallic to vitreous

Streak

Green

Transparency

Opaque to transparent

mineralrare

Nagashimalite

Hardness: ~6
Luster: Submetallic to vitreous
Streak: Green
Transparency: Opaque to transparent

Is this nagashimalite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch nagashimalite with a known reference. Nagashimalite sits at Mohs ~6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: green.
3
Read the luster
Hold the specimen under a strong light. Luster: submetallic to vitreous.
4
Match the color range
Compare against the expected color range: greenish black.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: aggregates.

Often confused with

Nagashimalite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Vesuvianite

Mohs 6-7

How to tell apart: Streak differs, so Nagashimalite leaves green, Vesuvianite leaves white; luster reads submetallic to vitreous on Nagashimalite and vitreous to resinous on Vesuvianite.

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Often found alongside nagashimalite

Minerals reported to co-occur with nagashimalite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Ba₄(V³⁺,Ti)₄Si₈B₂O₂₇(O,OH)₂Cl
Mohs hardness: ~6
Density: 4.08 g/cm³
Colors: Greenish black
Streak: Green
Luster: Submetallic to vitreous
Transparency: Opaque to transparent
Crystal system: Orthorhombic
Crystal habit: Aggregates
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In fissures cutting massive rhodonite ore in a bedded manganese deposit

Where rockhounds find nagashimalite

Classic worldwide localities

Mogurazawa mine, Kiryu, Gumma Prefecture, Japan

Field-hunting tip

Where it forms: In fissures cutting massive rhodonite ore in a bedded manganese deposit. If you start seeing rhodochrosite, rhodonite, barite in float, you are in the right ground. Typical habit: aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify nagashimalite?+

Mohs hardness is ~6. Luster: submetallic to vitreous. The streak is green. Common colors include greenish black.

Where is nagashimalite found?+

Notable localities include Mogurazawa mine, Kiryu, Gumma Prefecture, Japan.

Is nagashimalite safe to handle?+

Nagashimalite contains vanadium. Wash your hands afterwards, never grind or breathe the dust, and store it apart from specimens you handle often.

What rocks look like nagashimalite?+

Nagashimalite is most often confused with Vesuvianite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with nagashimalite?+

Nagashimalite commonly co-occurs with Rhodochrosite, Rhodonite, Barite, Barian roscoelite, Alabandite, Digenite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does nagashimalite form in?+

Where it forms: In fissures cutting massive rhodonite ore in a bedded manganese deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is nagashimalite used for?+

Nagashimalite is used in collector.

Find nagashimalite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.