Kumtyubeite is a very rare calcium silicate fluoride mineral discovered in the pyrometamorphic rocks of the Northern Caucasus. It typically forms small tabular crystals within high-temperature combustion metamorphic assemblages and is highly prized by advanced mineral collectors.

Hardness

5-6

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrareHatrurite Group family

Kumtyubeite

Hardness: 5-6
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this kumtyubeite?

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 kumtyubeite with a known reference. Kumtyubeite sits at Mohs 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. Kumtyubeite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Kumtyubeite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: light-pink, colorless.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals.

Often confused with

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

mineral

Hatrurite

Mohs 3

How to tell apart: Kumtyubeite is noticeably harder (Mohs 5-6 vs. 3).

Often found alongside kumtyubeite

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

All properties

Chemical formula: Ca₄(Si₂O₇)F₂
Mohs hardness: 5-6
Density: 3.17 g/cm³
Colors: Light-pink Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals
Cleavage: Distinct On (001), Particularly For OH:F ≈ 1
Rarity: Rare
Uses: Collector
Host rock: Pyrometamorphic Rocks

Where rockhounds find kumtyubeite

Classic worldwide localities

Kumtyube, Kabardino-Balkarian Republic, Russia

Field-hunting tip

Look in pyrometamorphic rocks country, the host setting where kumtyubeite typically forms. If you start seeing ettringite, portlandite, afwillite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kumtyubeite?+

Mohs hardness is 5-6. It typically shows a vitreous luster. The streak is white. Common colors include light-pink, colorless.

Where is kumtyubeite found?+

Notable localities include Kumtyube, Kabardino-Balkarian Republic, Russia.

What rocks look like kumtyubeite?+

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

What minerals are found with kumtyubeite?+

Kumtyubeite commonly co-occurs with Ettringite, Portlandite, Afwillite, Calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kumtyubeite form in?+

Kumtyubeite typically forms in pyrometamorphic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kumtyubeite used for?+

Kumtyubeite is used in collector.

Find kumtyubeite on the map

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