Watatsumiite is a rare manganese-bearing silicate mineral belonging to the pectolite group. It is typically found in manganese ore deposits as radiating, fibrous, or acicular aggregates with a distinct reddish-yellowish green hue.

Hardness

5.5-6

Mohs

Luster

Vitreous

Streak

White with a greenish tint

Transparency

Transparent

mineralrarePectolite Group family

Watatsumiite

Hardness: 5.5-6
Luster: Vitreous
Streak: White with a greenish tint
Transparency: Transparent

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Is this watatsumiite?

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 watatsumiite with a known reference. Watatsumiite sits at Mohs 5.5-6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white with a greenish tint.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: yellow green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: massive, prismatic.

Often confused with

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

mineral

Pectolite

Mohs 4.5-5

How to tell apart: Luster reads vitreous on Watatsumiite and silky, subvitreous on Pectolite.

Often found alongside watatsumiite

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

All properties

Chemical formula: LiNa₂KMn₂V₂Si₈O₂₄
Mohs hardness: 5.5-6
Density: 3.24 g/cm³
Colors: Yellow green
Streak: White with a greenish tint
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Massive, prismatic
Cleavage: Poor
Rarity: Rare
Uses: Collector
Host rock: In veinlets in a metamorphosed Mn deposit

Where rockhounds find watatsumiite

Classic worldwide localities

Tanohata mine, Iwate Prefecture, Japan (type locality)

Field-hunting tip

Where it forms: In veinlets in a metamorphosed Mn deposit. If you start seeing potassicleakeite, quartz, k-feldspar in float, you are in the right ground. Typical habit: massive, prismatic. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify watatsumiite?+

Mohs hardness is 5.5-6. Luster: vitreous. The streak is white with a greenish tint. Common colors include yellow green.

Where is watatsumiite found?+

Notable localities include Tanohata mine, Iwate Prefecture, Japan (type locality).

Is watatsumiite safe to handle?+

Watatsumiite 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 watatsumiite?+

Watatsumiite is most often confused with Pectolite, Serandite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with watatsumiite?+

Watatsumiite commonly co-occurs with Potassicleakeite, Quartz, K-feldspar, Serandite, Suzukite, Roscelite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does watatsumiite form in?+

Where it forms: In veinlets in a metamorphosed Mn deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is watatsumiite used for?+

Watatsumiite is used in collector.

Find watatsumiite on the map

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