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.

Hardness

3.5-4

Mohs

Luster

Adamantine

Streak

Yellow

Transparency

Translucent

mineralrare

Sillénite

Hardness: 3.5-4
Luster: Adamantine
Streak: Yellow
Transparency: Translucent

Is this sillénite?

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 sillénite with a known reference. Sillénite sits at Mohs 3.5-4 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Sillénite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Sillénite typically shows a adamantine luster.
4
Match the color range
Compare against the expected color range: yellow, yellowish-orange, brown.
5
Look at form & habit
Crystal system: cubic. Typical habit: equant crystals, massive.

Often confused with

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

mineral

Bismite

Mohs 4.5

How to tell apart: Streak differs — Sillénite leaves yellow, Bismite leaves white.

How to tell apart: Streak differs — Sillénite leaves yellow, Bismutite leaves white; luster reads adamantine on Sillénite and pearly on Bismutite.

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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: 3.5-4
Density: 8.3-8.4 g/cm³
Colors: Yellow Yellowish-orange Brown
Streak: Yellow
Luster: Adamantine
Transparency: Translucent
Crystal system: Cubic
Crystal habit: Equant Crystals, Massive
Cleavage: None
Rarity: Rare
Uses: Collector, Research
Host rock: Hydrothermal Veins
Typical price: $50-500 depending on specimen quality

Where rockhounds find sillénite

Classic worldwide localities

Johanngeorgenstadt, Saxony, Germany
Bismutite deposits, various localities

Field-hunting tip

Look in hydrothermal veins country — that is the host setting where sillénite typically forms. If you start seeing bismutite, bismite, quartz in float, you are in the right ground. Field specimens usually show a equant crystals, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sillénite?+

Mohs hardness is 3.5-4. It typically shows a adamantine luster. The streak is yellow. Common colors include yellow, yellowish-orange, brown.

Where is sillénite found?+

Notable localities include Johanngeorgenstadt, Saxony, Germany; Bismutite deposits, various localities.

How much is sillénite worth?+

Typical asking prices fall in the range of $50-500 depending on specimen quality. Quality, size, and provenance can move individual specimens well outside that range.

Is sillénite safe to handle?+

It contains toxic constituents. Contains bismuth and may be associated with trace heavy metals; wash hands after handling and avoid inhalation of dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like sillénite?+

Sillénite is most often confused with Bismite, Bismutite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with sillénite?+

Sillénite commonly co-occurs with Bismutite, Bismite, Quartz, Hematite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sillénite form in?+

Sillénite typically forms in hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is sillénite used for?+

Sillénite is used in collector, research.

Find sillénite on the map

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