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. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: silver-white, steel-gray, tin white, light steel gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: euhedral crystals, prismatic, striated.
Often confused with
Arsenopyrite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Arsenopyrite leaves black, Pyrite leaves greenish black to brownish black.
How to tell apart: Streak differs, so Arsenopyrite leaves black, Marcasite leaves grayish or brownish black.
How to tell apart: Streak differs, so Arsenopyrite leaves black, Cobaltite leaves grayish 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
- Euhedral crystals, prismatic, striated
- Cleavage
- Distinct on {101}; {010} in traces
- Rarity
- Common
- Uses
- Collector, Ore
- Host rock
- Of hydrothermal origin, typically one of the earliest minerals to form
Where rockhounds find arsenopyrite
24 mapped spotsClassic worldwide localities
- Franconia, Grafton Co., New Hampshire and Franklin, Sussex Co., New Jersey, USA
- Altenberg, Ehrenfriedersdorf, and Freiberg, Saxony, Germany
- Stari Trg mine, Trepča, Serbia
- Panasqueira, Portugal
- Sala, Tunaberg, Stollberg, Boliden, and Nordmark, Sweden
- Stratonik, Greece
Field-hunting tip
Where it forms: Of hydrothermal origin, typically one of the earliest minerals to form. If you start seeing pyrrhotite, pyrite, chalcopyrite in float, you are in the right ground. Typical habit: euhedral crystals, prismatic, striated. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Idaho, Montana, South Dakota. Start trip planning there.
More arsenopyrite photos
Common questions
How do you identify arsenopyrite?+
Where is arsenopyrite found?+
Can I find arsenopyrite in the United States?+
Is arsenopyrite safe to handle?+
What rocks look like arsenopyrite?+
What minerals are found with arsenopyrite?+
What kind of rock does arsenopyrite form in?+
What is arsenopyrite used for?+
Find arsenopyrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
