Maruyamaite is a very rare potassium-dominant member of the tourmaline group, formally described from specimens in Japan. It typically occurs as small, pale-yellow prisms in highly evolved granitic pegmatites. Collectors value it as a significant species for advanced systematic mineral collections.

Hardness

Mohs

Luster

Vitreous

Streak

White to very pale-brown

Transparency

Translucent to transparent

mineralrareTourmaline Group family

Maruyamaite

Hardness: ~7
Luster: Vitreous
Streak: White to very pale-brown
Transparency: Translucent to transparent

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Is this maruyamaite?

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 maruyamaite with a known reference. Maruyamaite sits at Mohs ~7, 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 to very pale-brown.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: pale brown, brown.
5
Look at form & habit
Crystal system: trigonal. Typical habit: prismatic crystals.

Often confused with

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

How to tell apart: Streak differs, so Maruyamaite leaves white to very pale-brown, Dravite leaves light brown, white.

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Often found alongside maruyamaite

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

All properties

Chemical formula: K(MgAl₂)(Al₅Mg)(BO₃)₃(Si₆O₁₈)(OH)₃O
Mohs hardness: ~7
Density: 3.081 g/cm³
Colors: Pale brown Brown
Streak: White to very pale-brown
Luster: Vitreous
Transparency: Translucent to transparent
Crystal system: Trigonal
Crystal habit: Prismatic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: From ultrahigh-pressure, diamond-bearing gneiss

Where rockhounds find maruyamaite

Classic worldwide localities

Kumdy-Kol area of the Kokchetav Massif, northern Kazakhstan

Field-hunting tip

Where it forms: From ultrahigh-pressure, diamond-bearing gneiss. If you start seeing diamond, quartz, k-feldspar in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify maruyamaite?+

Mohs hardness is ~7. Luster: vitreous. The streak is white to very pale-brown. Common colors include pale brown, brown.

Where is maruyamaite found?+

Notable localities include Kumdy-Kol area of the Kokchetav Massif, northern Kazakhstan.

What rocks look like maruyamaite?+

Maruyamaite is most often confused with Elbaite, Schorl, Dravite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with maruyamaite?+

Maruyamaite commonly co-occurs with Diamond, Quartz, K-feldspar. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does maruyamaite form in?+

Where it forms: From ultrahigh-pressure, diamond-bearing gneiss. Working float back to the host body is the standard way to chase a fresh occurrence.

What is maruyamaite used for?+

Maruyamaite is used in collector.

Find maruyamaite on the map

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