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.

Hardness

2.5

Mohs

Luster

Pearly

Streak

White

Transparency

Transparent

mineralrare

Portlandite

Hardness: 2.5
Luster: Pearly
Streak: White
Transparency: Transparent

Is this portlandite?

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 portlandite with a known reference. Portlandite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Portlandite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Portlandite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: white, colorless.
5
Look at form & habit
Crystal system: trigonal. Typical habit: platy or foliated masses.

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 Portlandite and vitreous on Gibbsite.

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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: 2.5
Density: 2.24 g/cm³
Colors: White Colorless
Streak: White
Luster: Pearly
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Platy or Foliated Masses
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector, Scientific Research
Host rock: Metamorphosed Limestone Adjacent to Igneous Contacts or in Combustion Metamorphic Environments
Typical price: $20-100 for small thumbnail specimens

Where rockhounds find portlandite

Classic worldwide localities

Scawt Hill, Northern Ireland
Maywood, New Jersey, USA
La Fossa Crater, Vulcano, Italy
Chelyabinsk, Russia

Field-hunting tip

Look in metamorphosed limestone adjacent to igneous contacts or in combustion metamorphic environments country, the host setting where portlandite typically forms. If you start seeing calcite, ettringite, afwillite in float, you are in the right ground. Field specimens usually show a platy or foliated masses habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify portlandite?+

Mohs hardness is 2.5. It typically shows a pearly luster. The streak is white. Common colors include white, colorless.

Where is portlandite found?+

Notable localities include Scawt Hill, Northern Ireland; Maywood, New Jersey, USA; La Fossa Crater, Vulcano, Italy; Chelyabinsk, Russia.

How much is portlandite worth?+

Typical asking prices fall in the range of $20-100 for small thumbnail specimens. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like portlandite?+

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

What minerals are found with portlandite?+

Portlandite commonly co-occurs with Calcite, Ettringite, Afwillite, Larnite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does portlandite form in?+

Portlandite typically forms in metamorphosed limestone adjacent to igneous contacts or in combustion metamorphic environments. Working float back to the host body is the standard way to chase a fresh occurrence.

What is portlandite used for?+

Portlandite is used in collector, scientific research.

Find portlandite on the map

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