Sosedkoite is an exceptionally rare potassium-aluminum-tantalum oxide mineral found in complex granite pegmatites. It typically occurs as small, distinct colorless tabular crystals associated with other rare tantalum species.

Hardness

3.5

Mohs

Luster

Adamantine

Streak

Yellow

Transparency

Transparent

mineralrare

Sosedkoite

Hardness: 3.5
Luster: Adamantine
Streak: Yellow
Transparency: Transparent

Is this sosedkoite?

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 sosedkoite with a known reference. Sosedkoite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Sosedkoite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Sosedkoite typically shows a adamantine luster.
4
Match the color range
Compare against the expected color range: colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: tabular crystals, platy.

Often found alongside sosedkoite

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

All properties

Chemical formula: (K,Na)₅Al₄(Ta,Nb,W)₁₀O₃₀
Mohs hardness: 3.5
Density: 6.9 g/cm³
Colors: Colorless
Streak: Yellow
Luster: Adamantine
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Tabular Crystals, Platy
Cleavage: Good
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites

Where rockhounds find sosedkoite

Classic worldwide localities

Mt. Vasin-Myl'k, Voron'i massif, Kola Peninsula, Russia

Field-hunting tip

Look in granite pegmatites country, the host setting where sosedkoite typically forms. If you start seeing muscovite, quartz, albite in float, you are in the right ground. Field specimens usually show a tabular crystals, platy habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sosedkoite?+

Mohs hardness is 3.5. It typically shows a adamantine luster. The streak is yellow. Common colors include colorless.

Where is sosedkoite found?+

Notable localities include Mt. Vasin-Myl'k, Voron'i massif, Kola Peninsula, Russia.

What minerals are found with sosedkoite?+

Sosedkoite commonly co-occurs with muscovite, quartz, albite, columbite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sosedkoite form in?+

Sosedkoite typically forms in granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is sosedkoite used for?+

Sosedkoite is used in collector.

Find sosedkoite on the map

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