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

Transparent

mineralrare

Dukeite

Hardness: 3-4
Luster: Resinous
Streak: Bright Yellow
Transparency: Transparent

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. Dukeite leaves a bright yellow streak.
3
Read the luster
Hold the specimen under a strong light. Dukeite typically shows a resinous luster.
4
Match the color range
Compare against the expected color range: yellow, orange-yellow.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: tabular crystals, crusts.

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 to 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
Mohs hardness: 3-4
Density: 7.18 g/cm³
Colors: Yellow Orange-yellow
Streak: Bright Yellow
Luster: Resinous
Transparency: Transparent
Crystal system: Hexagonal
Crystal habit: Tabular Crystals, Crusts
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Oxidized Hydrothermal Bismuth Deposits

Where rockhounds find dukeite

Classic worldwide localities

Minas Gerais, Brazil

Field-hunting tip

Look in oxidized hydrothermal bismuth deposits country, the host setting where dukeite typically forms. If you start seeing bismite, bismutite, quartz in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify dukeite?+

Mohs hardness is 3-4. It typically shows a resinous luster. The streak is bright yellow. Common colors include yellow, orange-yellow.

Where is dukeite found?+

Notable localities include Minas Gerais, Brazil.

Is dukeite safe to handle?+

It contains toxic constituents. Contains bismuth and chromium; avoid ingestion, inhalation of dust, or prolonged skin contact during handling. Handle with care, avoid grinding or breathing dust, and store separately.

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 bismite, bismutite, quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does dukeite form in?+

Dukeite typically forms in oxidized hydrothermal bismuth deposits. 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

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