Rösslerite is a rare magnesium arsenate mineral that typically forms as a secondary product in the oxidation zones of arsenic-rich ore deposits. It is most frequently encountered as delicate acicular crystals or white, fibrous efflorescent crusts on associated arsenate minerals.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Rösslerite

Hardness: 2-3
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this rösslerite?

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 rösslerite with a known reference. Rösslerite sits at Mohs 2-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Rösslerite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Rösslerite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless, pale yellow, pale green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: acicular crystals, efflorescent crusts, radial aggregates.

Often confused with

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

Often found alongside rösslerite

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

All properties

Chemical formula: Mg(HAsO₄)·7H₂O
Mohs hardness: 2-3
Density: 2.44 g/cm³
Colors: White Colorless Pale Yellow Pale Green
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Acicular Crystals, Efflorescent Crusts, Radial Aggregates
Cleavage: Perfect On {010}
Rarity: Rare
Uses: Collector
Host rock: Oxidized Zones of Arsenic-rich Hydrothermal Deposits
Typical price: $20-150 thumbnail

Where rockhounds find rösslerite

Classic worldwide localities

Jachymov, Czech Republic
Schneeberg, Germany
Guiting Power, UK

Field-hunting tip

Look in oxidized zones of arsenic-rich hydrothermal deposits country — that is the host setting where rösslerite typically forms. If you start seeing pharmacolite, scorodite, arsenopyrite in float, you are in the right ground. Field specimens usually show a acicular crystals, efflorescent crusts, radial aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify rösslerite?+

Mohs hardness is 2-3. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless, pale yellow, pale green.

Where is rösslerite found?+

Notable localities include Jachymov, Czech Republic; Schneeberg, Germany; Guiting Power, UK.

How much is rösslerite worth?+

Typical asking prices fall in the range of $20-150 thumbnail. Quality, size, and provenance can move individual specimens well outside that range.

Is rösslerite safe to handle?+

It contains toxic constituents. Contains arsenic, which is toxic. Handle with caution, avoid inhaling dust, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like rösslerite?+

Rösslerite is most often confused with Pharmacolite, Haidingerite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with rösslerite?+

Rösslerite commonly co-occurs with Pharmacolite, Scorodite, Arsenopyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does rösslerite form in?+

Rösslerite typically forms in oxidized zones of arsenic-rich hydrothermal deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is rösslerite used for?+

Rösslerite is used in collector.

Find rösslerite on the map

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