Londonite is a rare cesium-dominant member of the rhodizite group, typically found as small, sharp dodecahedral crystals in highly evolved pegmatites. It is visually indistinguishable from its potassium-rich counterpart rhodizite without chemical analysis, though londonite is generally rarer. Collectors prize these hard, lustrous crystals for their exceptional clarity and high-index brilliance.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrareRhodizite-Londonite Series family

Londonite

Hardness: 8
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this londonite?

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 londonite with a known reference. Londonite sits at Mohs 8, 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: white, colorless, yellow.
5
Look at form & habit
Crystal system: cubic. Typical habit: euhedral crystals.

Often confused with

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

How to tell apart: Londonite is noticeably harder (Mohs 8 vs. 7-7.25).

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Often found alongside londonite

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

All properties

Chemical formula: CsBe₅Al₄B₁₁O₂₈
Mohs hardness: 8
Density: 3.34 g/cm³
Colors: White Colorless Yellow
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Cubic
Crystal habit: Euhedral crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: An uncommon component of granite pegmatites, in the central zones and in miarolitic cavities

Where rockhounds find londonite

Classic worldwide localities

Antandrokomby, near Mt. Bity, Manandona Valley, Antsirabe district, Madagascar
Antsongombato and Ampanivana, south of Mahaiza, and from Manjaka, Betafo region, Madagascar

Field-hunting tip

Where it forms: An uncommon component of granite pegmatites, in the central zones and in miarolitic cavities. If you start seeing rhodizite, danburite, elbaite–liddicoatite–schorl in float, you are in the right ground. Typical habit: euhedral crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify londonite?+

Mohs hardness is 8. Luster: vitreous. The streak is white. Common colors include white, colorless, yellow.

Where is londonite found?+

Notable localities include Antandrokomby, near Mt. Bity, Manandona Valley, Antsirabe district, Madagascar; Antsongombato and Ampanivana, south of Mahaiza, and from Manjaka, Betafo region, Madagascar.

Is londonite safe to handle?+

Londonite contains beryllium. Wash your hands afterwards, never grind or breathe the dust, and store it apart from specimens you handle often.

What rocks look like londonite?+

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

What minerals are found with londonite?+

Londonite commonly co-occurs with Rhodizite, Danburite, Elbaite–liddicoatite–schorl, Cs-rich beryl, Spodumene, Mn-rich apatite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does londonite form in?+

Where it forms: An uncommon component of granite pegmatites, in the central zones and in miarolitic cavities. Working float back to the host body is the standard way to chase a fresh occurrence.

What is londonite used for?+

Londonite is used in collector.

Find londonite on the map

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