Boyleite is a rare secondary zinc sulfate mineral typically found as white crusts or efflorescences in the oxidized zones of zinc-rich sulfide deposits. It is structurally related to the Gunningite group and is highly water-soluble, making it a challenge for collectors to preserve in humid environments. It is most commonly identified by its occurrence as a late-stage weathering product in mines.

Hardness

Mohs

Luster

Vitreous to dull

Streak

White

Transparency

Semitransparent

mineralrareGunningite Group family

Boyleite

Hardness: ~2
Luster: Vitreous to dull
Streak: White
Transparency: Semitransparent

Is this boyleite?

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 boyleite with a known reference. Boyleite sits at Mohs ~2, 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 to dull.
4
Match the color range
Compare against the expected color range: white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: crusts, efflorescences, granular.

Often confused with

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

Often found alongside boyleite

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

All properties

Chemical formula: ZnSO₄·4H₂O
Mohs hardness: ~2
Density: 2.41 g/cm³
Colors: White
Streak: White
Luster: Vitreous to dull
Transparency: Semitransparent
Crystal system: Monoclinic
Crystal habit: Crusts, efflorescences, granular
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A rare alteration product of sphalerite in a hydrothermal Pb–Zn vein (Kropbach quarry, Germany)

Where rockhounds find boyleite

Classic worldwide localities

Kropbach quarry, Münstertal, Black Forest, Germany
Les Vallettes, Valais, Switzerland
Keno Hill, Yukon Territory, Canada

Field-hunting tip

Where it forms: A rare alteration product of sphalerite in a hydrothermal Pb–Zn vein (Kropbach quarry, Germany). If you start seeing gypsum, gunningite, sphalerite in float, you are in the right ground. Typical habit: crusts, efflorescences, granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify boyleite?+

Mohs hardness is ~2. Luster: vitreous to dull. The streak is white. Common colors include white.

Where is boyleite found?+

Notable localities include Kropbach quarry, Münstertal, Black Forest, Germany; Les Vallettes, Valais, Switzerland; Keno Hill, Yukon Territory, Canada.

What rocks look like boyleite?+

Boyleite is most often confused with Gunningite, Epsomite, Goslarite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with boyleite?+

Boyleite commonly co-occurs with Gypsum, Gunningite, Sphalerite, Coquimbite, Zincocopiapite, Jarosite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does boyleite form in?+

Where it forms: A rare alteration product of sphalerite in a hydrothermal Pb–Zn vein (Kropbach quarry, Germany). Working float back to the host body is the standard way to chase a fresh occurrence.

What is boyleite used for?+

Boyleite is used in collector.

Find boyleite on the map

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