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-dark red to black needle-like crystals associated with sulfur deposits in high-temperature volcanic environments.
Is this demicheleite-(i)?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry 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.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: dark red, black.
- 5Look at form & habitCrystal 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.
How to tell apart: Streak differs, so Demicheleite-(I) leaves brown, Realgar leaves red-orange to red; luster reads submetallic on Demicheleite-(I) and resinous to greasy on Realgar.
How to tell apart: Streak differs, so Demicheleite-(I) leaves brown, Sulfur leaves white; luster reads submetallic on Demicheleite-(I) and resinous on Sulfur.
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
- 6.411 g/cm³
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular crystals, crusts
- Cleavage
- None observed
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A product of fumarolic alteration of pyroclastic breccia
Where rockhounds find demicheleite-(i)
Classic worldwide localities
- La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy
Field-hunting tip
Where it forms: A product of fumarolic alteration of pyroclastic breccia. If you start seeing demicheleite-, bismoclite, bismuthinite in float, you are in the right ground. Typical habit: acicular crystals, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify demicheleite-(i)?+
Where is demicheleite-(i) found?+
Is demicheleite-(i) safe to handle?+
What rocks look like demicheleite-(i)?+
What minerals are found with demicheleite-(i)?+
What kind of rock does demicheleite-(i) form in?+
What is demicheleite-(i) used for?+
Find demicheleite-(i) on the map
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