Demicheleite-(I) is an extremely rare bismuth sulfoiodide mineral found as a sublimation product in active volcanic fumaroles. It typically appears as fine acicular, yellow-to-orange needle-like crystals associated with sulfur deposits in high-temperature volcanic environments.

Hardness

1.5-2

Mohs

Luster

Resinous

Streak

Yellow

Transparency

Translucent

mineralrare

Demicheleite-(I)

Hardness: 1.5-2
Luster: Resinous
Streak: Yellow
Transparency: Translucent

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Is this demicheleite-(i)?

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 demicheleite-(i) with a known reference. Demicheleite-(I) sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Demicheleite-(I) leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Demicheleite-(I) typically shows a resinous luster.
4
Match the color range
Compare against the expected color range: yellow, orange.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: acicular crystals, crusts.

Often confused with

Demicheleite-(I) vs. its common look-alikes — and how to tell them apart in the field.

mineral

Realgar

Mohs 1.5-2

How to tell apart: Streak differs — Demicheleite-(I) leaves yellow, Realgar leaves orange-red.

How to tell apart: Streak differs — Demicheleite-(I) leaves yellow, Sulfur leaves white.

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Often found alongside demicheleite-(i)

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

All properties

Chemical formula: BiSI
Mohs hardness: 1.5-2
Density: 4.15 g/cm³
Colors: Yellow Orange
Streak: Yellow
Luster: Resinous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Acicular Crystals, Crusts
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Fumarolic Deposits
Typical price: $100-500+ per specimen depending on size and quality

Where rockhounds find demicheleite-(i)

Classic worldwide localities

La Fossa crater, Vulcano, Aeolian Islands, Italy

Field-hunting tip

Look in fumarolic deposits country — that is the host setting where demicheleite-(i) typically forms. If you start seeing sulfur, realgar, bismuthinite in float, you are in the right ground. Field specimens usually show a acicular crystals, crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify demicheleite-(i)?+

Mohs hardness is 1.5-2. It typically shows a resinous luster. The streak is yellow. Common colors include yellow, orange.

Where is demicheleite-(i) found?+

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

How much is demicheleite-(i) worth?+

Typical asking prices fall in the range of $100-500+ per specimen depending on size and quality. Quality, size, and provenance can move individual specimens well outside that range.

Is demicheleite-(i) safe to handle?+

It contains toxic constituents. Contains bismuth, sulfur, and iodine; avoid inhalation of dust and wash hands thoroughly after handling to prevent ingestion of toxic components. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like demicheleite-(i)?+

Demicheleite-(I) is most often confused with Realgar, Sulfur. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with demicheleite-(i)?+

Demicheleite-(I) commonly co-occurs with Sulfur, Realgar, Bismuthinite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does demicheleite-(i) form in?+

Demicheleite-(I) typically forms in fumarolic deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is demicheleite-(i) used for?+

Demicheleite-(I) is used in collector.

Find demicheleite-(i) on the map

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