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Hydroxycalciopyrochlore is a rare member of the pyrochlore group often found in alkaline igneous environments like carbonatites. It typically occurs as small, well-formed octahedral crystals that are often radioactive due to trace elements like uranium and thorium.

Hardness
5-6
Mohs
Luster
Adamantine to greasy
Streak
Brown
Transparency
Translucent

Is this hydroxycalciopyrochlore?

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 hydroxycalciopyrochlore with a known reference. Hydroxycalciopyrochlore sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: brown.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: adamantine to greasy.
  • 4
    Match the color range
    Compare against the expected color range: brownish black, greenish black, black.
  • 5
    Look at form & habit
    Crystal system: cubic. Typical habit: octahedral crystals.

Often confused with

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

Dark brown pyrochlore octahedron
mineral
Pyrochlore
Mohs 5-5.5

How to tell apart: Luster reads adamantine to greasy on Hydroxycalciopyrochlore and vitreous to resinous on Pyrochlore.

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Often found alongside hydroxycalciopyrochlore

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

All properties

Chemical formula
(Ca,Na,U,□)₂(Nb,Ti)₂O₆(OH)
Mohs hardness
5-6
Density
5.10 g/cm³
Colors
Brownish blackGreenish blackBlack
Streak
Brown
Luster
Adamantine to greasy
Transparency
Translucent
Crystal system
Cubic
Crystal habit
Octahedral crystals
Cleavage
None
Rarity
Rare
Uses
Collector, Scientific research
Host rock
In a rare-earth deposit in an alkali feldspar granite

Where rockhounds find hydroxycalciopyrochlore

Classic worldwide localities

  • Maoniuping mine, Mianning County, Xichang prefecture, Sichuan Province, southwest People’s Republic of China

Field-hunting tip

Where it forms: In a rare-earth deposit in an alkali feldspar granite. If you start seeing calcite, barite, celestine in float, you are in the right ground. Typical habit: octahedral crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hydroxycalciopyrochlore?+
Mohs hardness is 5-6. Luster: adamantine to greasy. The streak is brown. Common colors include brownish black, greenish black, black.
Where is hydroxycalciopyrochlore found?+
Notable localities include Maoniuping mine, Mianning County, Xichang prefecture, Sichuan Province, southwest People’s Republic of China.
Is hydroxycalciopyrochlore safe to handle?+
Hydroxycalciopyrochlore contains uranium or thorium and calls for real care. Contains uranium and thorium; store in a shielded container and avoid inhalation of dust when handling samples.
What rocks look like hydroxycalciopyrochlore?+
Hydroxycalciopyrochlore is most often confused with Pyrochlore. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with hydroxycalciopyrochlore?+
Hydroxycalciopyrochlore commonly co-occurs with Calcite, Barite, Celestine, Albite, Aegirine, Aegirine-augite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does hydroxycalciopyrochlore form in?+
Where it forms: In a rare-earth deposit in an alkali feldspar granite. Working float back to the host body is the standard way to chase a fresh occurrence.
What is hydroxycalciopyrochlore used for?+
Hydroxycalciopyrochlore is used in collector, scientific research.

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