Dukeite is an extremely rare secondary bismuth chromate mineral found primarily in oxidized zones of ore deposits. Collectors typically look for its distinct yellow, tabular crystal forms that often occur as thin crusts on bismuth-rich host rock.

Hardness

3-4

Mohs

Luster

Resinous

Streak

Bright yellow

Transparency

Translucent

mineralrare

Dukeite

Hardness: 3-4
Luster: Resinous
Streak: Bright yellow
Transparency: Translucent

No image

Is this dukeite?

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 dukeite with a known reference. Dukeite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: bright yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: resinous.
4
Match the color range
Compare against the expected color range: yellow, dirty yellow brown.
5
Look at form & habit
Crystal system: trigonal. Typical habit: acicular, wheat sheaf.

Often confused with

Dukeite 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 Dukeite leaves bright yellow, Bismite leaves gray to yellow; luster reads resinous on Dukeite and subadamantine to dull, earthy on Bismite.

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Often found alongside dukeite

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

All properties

Chemical formula: Bi₂₄Cr₈O₅₇(OH)₆·3H₂O
Mohs hardness: 3-4
Density: 7.179 g/cm³
Colors: YellowDirty yellow brown
Streak: Bright yellow
Luster: Resinous
Transparency: Translucent
Crystal system: Trigonal
Crystal habit: Acicular, wheat sheaf
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: On a museum specimen of pucherite

Where rockhounds find dukeite

Classic worldwide localities

Lavra da Posse, São José de Brejaúba, Conceição do Mato Dentro County (specimen label indicates the São José Mine, Brejaúba), Minas Gerais, Brazil

Field-hunting tip

Where it forms: On a museum specimen of pucherite. If you start seeing pucherite, schumacherite, bismutite in float, you are in the right ground. Typical habit: acicular, wheat sheaf. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify dukeite?+

Mohs hardness is 3-4. Luster: resinous. The streak is bright yellow. Common colors include yellow, dirty yellow brown.

Where is dukeite found?+

Notable localities include Lavra da Posse, São José de Brejaúba, Conceição do Mato Dentro County (specimen label indicates the São José Mine, Brejaúba), Minas Gerais, Brazil.

Is dukeite safe to handle?+

Dukeite contains hexavalent chromium and calls for real care. Contains bismuth and chromium; avoid ingestion, inhalation of dust, or prolonged skin contact during handling.

What rocks look like dukeite?+

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

What minerals are found with dukeite?+

Dukeite commonly co-occurs with Pucherite, Schumacherite, Bismutite, Hechtsbergite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does dukeite form in?+

Where it forms: On a museum specimen of pucherite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is dukeite used for?+

Dukeite is used in collector.

Find dukeite on the map

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