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

Hardness

3-4

Mohs

Luster

Vitreous to adamantine

Streak

White

Transparency

Transparent

mineralrare

Steropesite

Hardness: 3-4
Luster: Vitreous to adamantine
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. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to adamantine.
4
Match the color range
Compare against the expected color range: pale lemon yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular.

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, so Steropesite leaves white, Hollandite leaves black; luster reads vitreous to adamantine on Steropesite and metallic, splendent on Hollandite.

Compare →

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: 5.737 g/cm³
Colors: Pale lemon yellow
Streak: White
Luster: Vitreous to adamantine
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A sublimate at an active high-temperature volcanic fumarole (~450 °C)

Where rockhounds find steropesite

Classic worldwide localities

La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy

Field-hunting tip

Where it forms: A sublimate at an active high-temperature volcanic fumarole (~450 °C). If you start seeing bismuthinite, lafossaite in float, you are in the right ground. Typical habit: tabular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify steropesite?+

Mohs hardness is 3-4. Luster: vitreous to adamantine. The streak is white. Common colors include pale lemon yellow.

Where is steropesite found?+

Notable localities include La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy.

Is steropesite safe to handle?+

Steropesite contains thallium and calls for real care. Contains thallium, which is highly toxic. Handle with gloves and wash hands thoroughly after contact; do not ingest or inhale dust.

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 Bismuthinite, Lafossaite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does steropesite form in?+

Where it forms: A sublimate at an active high-temperature volcanic fumarole (~450 °C). 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.