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.
Is this rösslerite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch rösslerite with a known reference. Rösslerite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to dull.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal 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
- 1.943 g/cm³
- Streak
- White
- Luster
- Vitreous to dull
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular crystals, efflorescent crusts, radial aggregates
- Cleavage
- {111}, imperfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in the oxidized zone of arsenic-bearing ore deposits
Where rockhounds find rösslerite
Classic worldwide localities
- White Caps mine, Manhattan district, Nye Co., Nevada, USA
- Bieber, near Hanau, and from the Bauhaus district, Richelsdorf Mountains, Hesse, Germany
- Sophia mine, near Wittichen, from the Anton mine, Heubachtal, near Schiltach, and in the Wolfgang mine, near Alpirsbach, Black Forest, Germany
- St. Andreasberg, Harz Mountains, Germany
- Long fibers from Jáchymov (Joachimsthal), Czech Republic
Field-hunting tip
Where it forms: A secondary mineral in the oxidized zone of arsenic-bearing ore deposits. If you start seeing pharmacolite, haidingerite, picropharmacolite in float, you are in the right ground. Typical habit: acicular crystals, efflorescent crusts, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rösslerite?+
Where is rösslerite found?+
Is rösslerite safe to handle?+
What rocks look like rösslerite?+
What minerals are found with rösslerite?+
What kind of rock does rösslerite form in?+
What is rösslerite used for?+
Find rösslerite on the map
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