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Thorosteenstrupine is a rare thorium-rich silicate mineral typically found in highly alkaline igneous complexes. It is closely related to the steenstrupine group and is valued primarily by advanced mineral collectors due to its distinct radioactivity and locality-specific occurrence.

Hardness
~4
Mohs
Luster
Greasy to vitreous
Streak
Dark brown
Transparency
Opaque, translucent in thin fragments

Is this thorosteenstrupine?

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 thorosteenstrupine with a known reference. Thorosteenstrupine sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: dark brown.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: greasy to vitreous.
  • 4
    Match the color range
    Compare against the expected color range: dark brown, black, black brown.
  • 5
    Look at form & habit
    Crystal system: amorphous. Typical habit: tabular crystals, massive, granular.

Often confused with

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

Thorite mineral
mineral
Thorite
Mohs 4.5-5

How to tell apart: Streak differs, so Thorosteenstrupine leaves dark brown, Thorite leaves light orange to dark brown; luster reads greasy to vitreous on Thorosteenstrupine and vitreous to resinous or greasy on Thorite.

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Often found alongside thorosteenstrupine

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

All properties

Chemical formula
(Ca,Th,Mn,Mn)₃Si₄O₁₁F·6H₂O
Mohs hardness
~4
Density
3.02 g/cm³
Colors
Dark brownBlackBlack brown
Streak
Dark brown
Luster
Greasy to vitreous
Transparency
Opaque, translucent in thin fragments
Crystal system
Amorphous
Crystal habit
Tabular crystals, massive, granular
Cleavage
None
Rarity
Rare
Uses
Collector
Host rock
In metasomatic veins

Where rockhounds find thorosteenstrupine

Classic worldwide localities

  • Unspecified locality in eastern Siberia, Russia (type locality)

Field-hunting tip

Where it forms: In metasomatic veins. If you start seeing microcline, albite, aegirine-augite in float, you are in the right ground. Typical habit: tabular crystals, massive, granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thorosteenstrupine?+
Mohs hardness is ~4. Luster: greasy to vitreous. The streak is dark brown. Common colors include dark brown, black, black brown.
Where is thorosteenstrupine found?+
Notable localities include Unspecified locality in eastern Siberia, Russia (type locality).
Is thorosteenstrupine safe to handle?+
Thorosteenstrupine contains uranium or thorium and calls for real care. This mineral contains thorium and is radioactive; handle with care, use gloves, and store in a lead-lined or secure container away from living spaces.
What rocks look like thorosteenstrupine?+
Thorosteenstrupine is most often confused with Thorite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with thorosteenstrupine?+
Thorosteenstrupine commonly co-occurs with Microcline, Albite, Aegirine-augite, Quartz, Fluorite, Thorite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does thorosteenstrupine form in?+
Where it forms: In metasomatic veins. Working float back to the host body is the standard way to chase a fresh occurrence.
What is thorosteenstrupine used for?+
Thorosteenstrupine is used in collector.

Find thorosteenstrupine on the map

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