Tumchaite is an extremely rare silicate mineral discovered in the alkaline pegmatites of the Tumcha complex in Russia. It typically occurs as small, clear, tabular crystals associated with other rare zirconium minerals in agpaitic rock environments.

Hardness

~4.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrare

Tumchaite

Hardness: ~4.5
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this tumchaite?

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 tumchaite with a known reference. Tumchaite sits at Mohs ~4.5, 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.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: colorless.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: massive, prismatic.

Often confused with

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

How to tell apart: Wadeite is the harder of the two (Mohs 6-6.5 vs. ~4.5); luster reads vitreous on Tumchaite and adamantine on Wadeite.

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Often found alongside tumchaite

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

All properties

Chemical formula: Na₂ZrSi₄O₁₁·2H₂O
Mohs hardness: ~4.5
Density: 2.78 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Monoclinic
Crystal habit: Massive, prismatic
Cleavage: Perfect on (100)
Rarity: Rare
Uses: Collector
Host rock: As a lens-like segregation in a core sample from a bore hole, which crosscuts veined dolomite-calcite carbonatites occurring in pyroxenites

Where rockhounds find tumchaite

Classic worldwide localities

Vuoriyarvi alkali-ultrabasic massif, Murmansk region, Russia (type locality)

Field-hunting tip

Where it forms: As a lens-like segregation in a core sample from a bore hole, which crosscuts veined dolomite-calcite carbonatites occurring in pyroxenites. If you start seeing calcite, dolomite, pyrite 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 tumchaite?+

Mohs hardness is ~4.5. Luster: vitreous. The streak is white. Common colors include colorless.

Where is tumchaite found?+

Notable localities include Vuoriyarvi alkali-ultrabasic massif, Murmansk region, Russia (type locality).

What rocks look like tumchaite?+

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

What minerals are found with tumchaite?+

Tumchaite commonly co-occurs with Calcite, Dolomite, Pyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does tumchaite form in?+

Where it forms: As a lens-like segregation in a core sample from a bore hole, which crosscuts veined dolomite-calcite carbonatites occurring in pyroxenites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is tumchaite used for?+

Tumchaite is used in collector.

Find tumchaite on the map

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