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, 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
How do you identify londonite?+
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Find londonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
