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, so Sillénite leaves yellow, Bismite leaves white.

How to tell apart: Streak differs, so 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, 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.