Kollerite is a rare hydrated sodium iron arsenate that typically forms as a secondary mineral in oxidized arsenic-rich ore deposits. It is most frequently encountered by collectors as delicate, acicular, or fibrous yellow crusts on host rocks like weathered arsenopyrite.
Is this kollerite?
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 kollerite with a known reference. Kollerite 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. Kollerite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Kollerite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, pale yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular crystals, efflorescent crusts.
Often confused with
Kollerite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside kollerite
Minerals reported to co-occur with kollerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na(Fe³⁺,Al)₃(AsO₄)₂(OH)₄·7H₂O
- Mohs hardness
- 2-3
- Density
- 2.8 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular Crystals, Efflorescent Crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Arsenic-rich Hydrothermal Deposits
- Typical price
- $50-200 for micro-mount or small thumbnail specimens
Where rockhounds find kollerite
Classic worldwide localities
- Klodnitsa, Bulgaria
- Jachymov, Czech Republic
Field-hunting tip
Look in oxidized zones of arsenic-rich hydrothermal deposits country — that is the host setting where kollerite typically forms. If you start seeing arsenopyrite, goethite, gypsum in float, you are in the right ground. Field specimens usually show a acicular crystals, efflorescent crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kollerite?+
Where is kollerite found?+
How much is kollerite worth?+
Is kollerite safe to handle?+
What rocks look like kollerite?+
What minerals are found with kollerite?+
What kind of rock does kollerite form in?+
What is kollerite used for?+
Find kollerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
