Arsenopyrite is the most common arsenic-bearing mineral, easily identified by its silver-white metallic appearance and distinct garlic-like odor when struck with a hammer. It frequently occurs as well-formed prismatic crystals or dense massive aggregates in hydrothermal sulfide veins. Due to its arsenic content, collectors should handle specimens with care and wash hands thoroughly after cleaning.
Is this arsenopyrite?
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 arsenopyrite with a known reference. Arsenopyrite sits at Mohs 5.5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Arsenopyrite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Arsenopyrite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: silver-white, steel-gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, massive, granular.
Often confused with
Arsenopyrite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Arsenopyrite leaves black, Pyrite leaves greenish-black to brownish-black.
How to tell apart: Streak differs — Arsenopyrite leaves black, Marcasite leaves greyish-black.
How to tell apart: Streak differs — Arsenopyrite leaves black, Cobaltite leaves greyish-black.
Often found alongside arsenopyrite
Minerals reported to co-occur with arsenopyrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeAsS
- Mohs hardness
- 5.5-6
- Density
- 6.07 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Massive, Granular
- Cleavage
- Distinct
- Rarity
- Common
- Uses
- Collector, Ore
- Host rock
- Hydrothermal Veins
- Typical price
- $10-100 per specimen
Where rockhounds find arsenopyrite
25 mapped spotsClassic worldwide localities
- Freiberg, Germany
- Panasqueira, Portugal
- Boliden, Sweden
- Naica, Mexico
- Cobalt, Canada
Field-hunting tip
Look in hydrothermal veins country — that is the host setting where arsenopyrite typically forms. If you start seeing quartz, pyrite, galena in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Idaho, Maine, Montana — start trip planning there.
Common questions
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Find arsenopyrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
