Nyholmite is a rare zinc-copper arsenate mineral discovered in the Broken Hill mining district. It typically appears as small, white to colorless bladed crystals or clusters formed within the oxidized zones of ore deposits.

Hardness

3-3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrareHopeite Group family

Nyholmite

Hardness: 3-3.5
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

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Is this nyholmite?

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 nyholmite with a known reference. Nyholmite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: colorless crystals, white in aggregates.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: bladed crystals, aggregates.

Often confused with

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

How to tell apart: Luster reads vitreous on Nyholmite and subadamantine to silky in aggregates on Austinite.

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Often found alongside nyholmite

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

All properties

Chemical formula: Cd₃Zn₂(AsO₃OH)₂(AsO₄)₂·4H₂O
Mohs hardness: 3-3.5
Density: 4.42 g/cm³
Colors: Colorless crystalsWhite in aggregates
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Monoclinic
Crystal habit: Bladed crystals, aggregates
Cleavage: Perfect on {001}
Rarity: Rare
Uses: Collector
Host rock: A late-stage secondary mineral in the weathering zone of a Cd-Zn arsenate deposit

Where rockhounds find nyholmite

Classic worldwide localities

Block 14 Opencut, Broken Hill, New South Wales, Australia

Field-hunting tip

Where it forms: A late-stage secondary mineral in the weathering zone of a Cd-Zn arsenate deposit. If you start seeing goldquarryite, lavendulan-sampleite, scorodite-strengite in float, you are in the right ground. Typical habit: bladed crystals, aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify nyholmite?+

Mohs hardness is 3-3.5. Luster: vitreous. The streak is white. Common colors include colorless crystals, white in aggregates.

Where is nyholmite found?+

Notable localities include Block 14 Opencut, Broken Hill, New South Wales, Australia.

Is nyholmite safe to handle?+

Nyholmite contains arsenic and cadmium and calls for real care. Contains arsenic and copper; avoid ingestion, inhalation of dust, and wash hands thoroughly after handling specimens.

What rocks look like nyholmite?+

Nyholmite is most often confused with Hopeite, Spencerite, Austinite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with nyholmite?+

Nyholmite commonly co-occurs with Goldquarryite, Lavendulan-sampleite, Scorodite-strengite, Gypsum. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does nyholmite form in?+

Where it forms: A late-stage secondary mineral in the weathering zone of a Cd-Zn arsenate deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is nyholmite used for?+

Nyholmite is used in collector.

Find nyholmite on the map

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