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.
Is this londonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch londonite with a known reference. Londonite sits at Mohs 8 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Londonite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Londonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellow, yellowish-white.
- 5Look at form & habitCrystal system: isometric. Typical habit: dodecahedral crystals.
Often confused with
Londonite vs. its common look-alikes — and how to tell them apart in the field.
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
- (Cs,K)Be₄Al₄(B,Be)₁₂O₂₈
- Mohs hardness
- 8
- Density
- 3.37 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Isometric
- Crystal habit
- Dodecahedral Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $50-500 depending on crystal size and quality
Where rockhounds find londonite
Classic worldwide localities
- Antsongombato, Madagascar
- Sahatany Pegmatite Field, Madagascar
Field-hunting tip
Look in granite pegmatites country — that is the host setting where londonite typically forms. If you start seeing quartz, albite, tourmaline in float, you are in the right ground. Field specimens usually show a dodecahedral crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find londonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
