Portlandite is a rare calcium hydroxide mineral typically found in metamorphosed limestone or industrial sites where cement has hydrated. It usually appears as white, platy masses or foliated aggregates with a distinct pearly luster, closely resembling brucite. Collectors should handle it carefully as it is prone to degradation by atmospheric carbon dioxide.
Is this portlandite?
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 portlandite with a known reference. Portlandite sits at Mohs 2, 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 on cleavages.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: trigonal. Typical habit: hexagonal, platy.
Often confused with
Portlandite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads pearly on cleavages on Portlandite and waxy, pearly on cleavage surfaces on Brucite.
How to tell apart: Luster reads pearly on cleavages on Portlandite and vitreous, pearly on cleavage surfaces, dull in aggregates on Gibbsite.
Often found alongside portlandite
Minerals reported to co-occur with portlandite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(OH)₂
- Mohs hardness
- 2
- Density
- 2.23 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly on cleavages
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal, platy
- Cleavage
- {0001}, perfect
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- An alteration product of calcium silicates in larnite-spurrite contact metamorphic rocks (Scawt Hill, Ireland); in fumaroles (Vesuvius, Italy)
Where rockhounds find portlandite
Classic worldwide localities
- Scawt Hill, Larne, Co. Antrim, Ireland
- Vesuvius, Campania, Italy
- Bellerberg volcano, two km north of Mayen, Eifel district, Germany
- Chelyabinsk coal basin, Southern Ural Mountains, Russia
- Hatrurim Formation, Israel
- Maqarin area, north Jordan
Field-hunting tip
Where it forms: An alteration product of calcium silicates in larnite-spurrite contact metamorphic rocks (Scawt Hill, Ireland); in fumaroles (Vesuvius, Italy). If you start seeing afwillite, calcite, larnite in float, you are in the right ground. Typical habit: hexagonal, platy. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify portlandite?+
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What rocks look like portlandite?+
What minerals are found with portlandite?+
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Find portlandite on the map
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