Hydroxycalciomicrolite is a rare member of the pyrochlore supergroup typically found as small, distinct octahedral crystals within granitic pegmatites. It is often yellowish to brownish in color and is notable for its radioactivity, which may require specific storage considerations for collectors.

Hardness

5-6

Mohs

Luster

Vitreous to resinous

Streak

White

Transparency

Translucent

mineralrarePyrochlore Supergroup family

Hydroxycalciomicrolite

Hardness: 5-6
Luster: Vitreous to resinous
Streak: White
Transparency: Translucent

Is this hydroxycalciomicrolite?

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 hydroxycalciomicrolite with a known reference. Hydroxycalciomicrolite 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: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to resinous.
4
Match the color range
Compare against the expected color range: yellow.
5
Look at form & habit
Crystal system: cubic. Typical habit: octahedral crystals.

Often confused with

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

mineral

Pyrochlore

Mohs 5-5.5

How to tell apart: Streak differs, so Hydroxycalciomicrolite leaves white, Pyrochlore leaves brown.

Compare →

Often found alongside hydroxycalciomicrolite

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

All properties

Chemical formula: (Ca,◻)₂Ta₂O₆(OH)
Mohs hardness: 5-6
Density: 6.176 g/cm³
Colors: Yellow
Streak: White
Luster: Vitreous to resinous
Transparency: Translucent
Crystal system: Cubic
Crystal habit: Octahedral crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In heavy mineral concentrates from a complex granitic pegmatite

Where rockhounds find hydroxycalciomicrolite

Classic worldwide localities

Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil

Field-hunting tip

Where it forms: In heavy mineral concentrates from a complex granitic pegmatite. If you start seeing hydrokenomicrolite, fluorcalciomicrolite 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 hydroxycalciomicrolite?+

Mohs hardness is 5-6. Luster: vitreous to resinous. The streak is white. Common colors include yellow.

Where is hydroxycalciomicrolite found?+

Notable localities include Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil.

Is hydroxycalciomicrolite safe to handle?+

Hydroxycalciomicrolite contains trace uranium or thorium. Contains radioactive elements (typically U or Th impurities); handle with care and wash hands thoroughly after handling. Store away from other minerals to prevent cross-contamination.

What rocks look like hydroxycalciomicrolite?+

Hydroxycalciomicrolite 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 hydroxycalciomicrolite?+

Hydroxycalciomicrolite commonly co-occurs with Hydrokenomicrolite, Fluorcalciomicrolite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hydroxycalciomicrolite form in?+

Where it forms: In heavy mineral concentrates from a complex granitic pegmatite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hydroxycalciomicrolite used for?+

Hydroxycalciomicrolite is used in collector.

Find hydroxycalciomicrolite on the map

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