Sillénite is a rare bismuth silicate mineral typically found in oxidation zones of bismuth-bearing hydrothermal deposits. It is best identified by its high density and adamantine luster, occurring most frequently as small, yellowish cubic crystals.
Is this sillénite?
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 sillénite with a known reference. Sillénite sits at Mohs 1-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light yellowish to brownish white.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: brownish green, green, gray green, yellow green, olive green.
- 5Look at form & habitCrystal system: cubic. Typical habit: cubic crystals, earthy, massive.
Often confused with
Sillénite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Bismite is the harder of the two (Mohs 4.5 vs. 1-2); streak differs, so Sillénite leaves light yellowish to brownish white, Bismite leaves gray to yellow; luster reads adamantine on Sillénite and subadamantine to dull, earthy on Bismite.
How to tell apart: Streak differs, so Sillénite leaves light yellowish to brownish white, Bismutite leaves gray; luster reads adamantine on Sillénite and vitreous, waxy, may be dull to earthy on Bismutite.
Often found alongside sillénite
Minerals reported to co-occur with sillénite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Bi₁₂SiO₂₀
- Mohs hardness
- 1-2
- Density
- 9.16 g/cm³
- Streak
- Light yellowish to brownish white
- Luster
- Adamantine
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Cubic crystals, earthy, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Research
- Host rock
- A secondary mineral formed by the oxidation of bismuth-bearing minerals (Durango, Mexico); in a hydrothermal vein in skarns (Fuka, Japan)
Where rockhounds find sillénite
Classic worldwide localities
- An unspecified locality in Durango, and at Munihuaza, near Alamos, Sonora, Mexico
- Monapo pegmatite, Mocambique district, Mozambique
- Fujikawachi, Oita Prefecture, Japan
- Fuka, near Bicchu, Okayama Prefecture, Japan
- Ishikawa, Fukushima Prefecture, Japan
- Smrkovec, Slavkovský Les Mountains, about 10 km north-northeast of Mariánské Lázně, Czech Republic
Field-hunting tip
Where it forms: A secondary mineral formed by the oxidation of bismuth-bearing minerals (Durango, Mexico); in a hydrothermal vein in skarns (Fuka, Japan). If you start seeing bismutite, shattuckite, ajoite in float, you are in the right ground. Typical habit: cubic crystals, earthy, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify sillénite?+
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Find sillénite on the map
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