Combeite is an extremely rare silicate mineral found in alkaline volcanic environments. It is best known from the unique lavas of Mount Nyiragongo and Oldoinyo Lengai, where it occurs in small, colorless to pale yellow grains associated with nepheline and melilite.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralrare

Combeite

Hardness: 5
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this combeite?

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 combeite with a known reference. Combeite sits at Mohs 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: trigonal. Typical habit: granular to prismatic crystals.

Often confused with

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

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

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Often found alongside combeite

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

All properties

Chemical formula: Na₄.₅Ca₃.₅Si₆O₁₇.₅(OH)₀.₅
Mohs hardness: 5
Density: 2.844 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Trigonal
Crystal habit: Granular to prismatic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In nephelinite (Mt. Shaheru, Congo); in nephelinite and ash ejecta (Oldoinyo Lengai volcano, Tanzania)

Where rockhounds find combeite

Classic worldwide localities

Mt. Shaheru, the extinct southern cone of Mt. Nyiragongo, Kivu Province, Congo (Zaire)
Oldoinyo Lengai volcano, Tanzania

Field-hunting tip

Where it forms: In nephelinite (Mt. Shaheru, Congo); in nephelinite and ash ejecta (Oldoinyo Lengai volcano, Tanzania). If you start seeing götzenite, wollastonite, clinopyroxene in float, you are in the right ground. Typical habit: granular to prismatic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify combeite?+

Mohs hardness is 5. Luster: vitreous. The streak is white. Common colors include colorless.

Where is combeite found?+

Notable localities include Mt. Shaheru, the extinct southern cone of Mt. Nyiragongo, Kivu Province, Congo (Zaire); Oldoinyo Lengai volcano, Tanzania.

What rocks look like combeite?+

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

What minerals are found with combeite?+

Combeite commonly co-occurs with Götzenite, Wollastonite, Clinopyroxene, Nepheline, Melilite, Titanian garnet. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does combeite form in?+

Where it forms: In nephelinite (Mt. Shaheru, Congo); in nephelinite and ash ejecta (Oldoinyo Lengai volcano, Tanzania). Working float back to the host body is the standard way to chase a fresh occurrence.

What is combeite used for?+

Combeite is used in collector.

Find combeite on the map

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