Steropesite is an extremely rare thallium bismuth chloride mineral discovered in volcanic fumaroles. It typically occurs as tiny, tabular, colorless to white crystals that are chemically complex and unstable in humid environments.

Hardness

3-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Steropesite

Hardness: 3-4
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this steropesite?

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 steropesite with a known reference. Steropesite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Steropesite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Steropesite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals.

Often confused with

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

mineral

Hollandite

Mohs 6

How to tell apart: Hollandite is the harder of the two (Mohs 6 vs. 3-4); streak differs — Steropesite leaves white, Hollandite leaves black; luster reads vitreous on Steropesite and metallic on Hollandite.

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Often found alongside steropesite

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

All properties

Chemical formula: Tl₃BiCl₆
Mohs hardness: 3-4
Density: 2.98 g/cm³
Colors: Colorless White
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals
Cleavage: Good
Rarity: Rare
Uses: Collector
Host rock: Fumarolic Deposits
Typical price: $200-1000+ for rare micro specimens

Where rockhounds find steropesite

Classic worldwide localities

La Fossa Crater, Vulcano, Lipari Islands, Italy

Field-hunting tip

Look in fumarolic deposits country — that is the host setting where steropesite typically forms. If you start seeing adranosite, demidovite, bismuthinite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify steropesite?+

Mohs hardness is 3-4. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white.

Where is steropesite found?+

Notable localities include La Fossa Crater, Vulcano, Lipari Islands, Italy.

How much is steropesite worth?+

Typical asking prices fall in the range of $200-1000+ for rare micro specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is steropesite safe to handle?+

It contains toxic constituents. Contains thallium, which is highly toxic. Handle with gloves and wash hands thoroughly after contact; do not ingest or inhale dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like steropesite?+

Steropesite is most often confused with Hollandite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with steropesite?+

Steropesite commonly co-occurs with adranosite, demidovite, bismuthinite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does steropesite form in?+

Steropesite typically forms in fumarolic deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is steropesite used for?+

Steropesite is used in collector.

Find steropesite on the map

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