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, 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.