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Pseudomarkeyite is a rare pseudomorph where calcium carbonate (calcite) has replaced the unstable mineral ikaite, which typically forms in cold marine sediments. Collectors prize these for their unique, often elongated or 'fleur-de-lis' crystal shapes that retain the structural history of the original ikaite phase. They are typically found in glacial-marine sediments and require careful handling due to the fragile nature of these pseudomorphs.

Hardness
3
Mohs
Luster
Vitreous
Streak
White
Transparency
Transparent

Is this pseudomarkeyite?

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 pseudomarkeyite with a known reference. Pseudomarkeyite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: white.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: vitreous.
  • 4
    Match the color range
    Compare against the expected color range: pale green-yellow.
  • 5
    Look at form & habit
    Crystal system: monoclinic. Typical habit: pseudomorphs after ikaite.

Often confused with

Pseudomarkeyite vs. its common look-alikes, and how to tell them apart in the field.

Ikaite mineral
mineral
Ikaite
Mohs 2.5

How to tell apart: Luster reads vitreous on Pseudomarkeyite and earthy on Ikaite.

Compare →
Golden scalenohedral calcite crystal, Elmwood Mine, Tennessee
mineral
Calcite
Mohs 3
Compare →

Often found alongside pseudomarkeyite

Minerals reported to co-occur with pseudomarkeyite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula
Ca₈(UO₂)₄(CO₃)₁₂(H₂O)₁₈·3H₂O
Mohs hardness
3
Density
2.71 g/cm³
Colors
Pale green-yellow
Streak
White
Luster
Vitreous
Transparency
Transparent
Crystal system
Monoclinic
Crystal habit
Pseudomorphs after ikaite
Cleavage
Perfect rhombohedral
Rarity
Rare
Uses
Collector
Host rock
sedimentary marine deposits

Where rockhounds find pseudomarkeyite

Classic worldwide localities

  • Greenland
  • Canada
  • Norway

Field-hunting tip

Where it forms: sedimentary marine deposits. If you start seeing calcite, aragonite in float, you are in the right ground. Typical habit: pseudomorphs after ikaite. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify pseudomarkeyite?+
Mohs hardness is 3. Luster: vitreous. The streak is white. Common colors include pale green-yellow.
Where is pseudomarkeyite found?+
Notable localities include Greenland; Canada; Norway.
Is pseudomarkeyite safe to handle?+
Pseudomarkeyite contains uranium or thorium and calls for real care. Wash your hands afterwards, never grind or breathe the dust, and store it apart from specimens you handle often.
What rocks look like pseudomarkeyite?+
Pseudomarkeyite is most often confused with Ikaite, Calcite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with pseudomarkeyite?+
Pseudomarkeyite commonly co-occurs with Calcite, Aragonite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does pseudomarkeyite form in?+
Where it forms: sedimentary marine deposits. Working float back to the host body is the standard way to chase a fresh occurrence.
What is pseudomarkeyite used for?+
Pseudomarkeyite is used in collector.

Find pseudomarkeyite on the map

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