Cesiodymite is a rare cesium-rich member of the mica group, primarily found in complex granitic pegmatites. Collectors look for its characteristic platy, mica-like morphology and its distinct chemical composition, which often occurs in association with pollucite and other rare pegmatite minerals.

Hardness

2.5-3

Mohs

Luster

Pearly

Streak

White

Transparency

Transparent

mineralrareMicas Group family

Cesiodymite

Hardness: 2.5-3
Luster: Pearly
Streak: White
Transparency: Transparent

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Is this cesiodymite?

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 cesiodymite with a known reference. Cesiodymite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Cesiodymite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Cesiodymite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: colorless, white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy crystals.

Often confused with

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

Often found alongside cesiodymite

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

All properties

Chemical formula: CsMg₃AlSi₃O₁₀(OH)₂
Mohs hardness: 2.5-3
Density: 3.16 g/cm³
Colors: Colorless White
Streak: White
Luster: Pearly
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Platy Crystals
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites
Typical price: $100-500 per specimen

Where rockhounds find cesiodymite

Classic worldwide localities

Kola Peninsula, Russia

Field-hunting tip

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

Common questions

How do you identify cesiodymite?+

Mohs hardness is 2.5-3. It typically shows a pearly luster. The streak is white. Common colors include colorless, white.

Where is cesiodymite found?+

Notable localities include Kola Peninsula, Russia.

How much is cesiodymite worth?+

Typical asking prices fall in the range of $100-500 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like cesiodymite?+

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

What minerals are found with cesiodymite?+

Cesiodymite commonly co-occurs with Microcline, Quartz, Albite, Pollucite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cesiodymite form in?+

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

What is cesiodymite used for?+

Cesiodymite is used in collector.

Find cesiodymite on the map

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