Plombièrite is a rare calcium silicate hydrate typically found as a result of hydrothermal activity, often in association with hot springs or as a secondary mineral in carbonate rocks. Collectors should look for delicate, white, platy or fibrous aggregates in the cavities of altered limestone.
Is this plombièrite?
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 plombièrite with a known reference. Plombièrite sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: amorphous, massive.
Often confused with
Plombièrite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Plombièrite is noticeably harder (Mohs ~4 vs. 2.5); luster reads pearly on Plombièrite and vitreous, silky in fibrous aggregates on Tobermorite.
How to tell apart: Luster reads pearly on Plombièrite and vitreous to pearly on Gyrolite.
How to tell apart: Xonotlite is the harder of the two (Mohs 6-6.5 vs. ~4).
Often found alongside plombièrite
Minerals reported to co-occur with plombièrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- [Ca(H₂O)₅]Ca₄Si₆O₁₆(OH)₂(H₂O)₂
- Mohs hardness
- ~4
- Density
- 2.02-2.20 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Amorphous, massive
- Cleavage
- Perfect
- Fluorescence
- Yellow cream-white under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Deposited in thermal waters on brick and mortor of an old Roman aqueduct at Ballycraigy, Larne, County Antrim, Northern Ireland
Where rockhounds find plombièrite
Classic worldwide localities
- Crestmore, Riverside Co., California, USA
- Ballycraigy and Scawt Hill, near Larne, and Carneal, Co. Antrim, Ireland
- Klöch, Styria, Austria
- Hatrurim Formation, Israel
- Fuka, near Bicchu, Okayama Prefecture, Japan
Field-hunting tip
Where it forms: Deposited in thermal waters on brick and mortor of an old Roman aqueduct at Ballycraigy, Larne, County Antrim, Northern Ireland. If you start seeing calcite, apophyllite, zeolites in float, you are in the right ground. Typical habit: amorphous, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify plombièrite?+
Where is plombièrite found?+
What rocks look like plombièrite?+
What minerals are found with plombièrite?+
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What is plombièrite used for?+
Find plombièrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
