Arsenopyrite
Arsenopyrite is sulfide (arsenide), FeAsS. In the hand, it rates 5.5 to 6 on the Mohs scale, and it runs silver white and steel gray. Silver-white wedge-shaped metallic crystals, brighter and whiter than pyrite, striated and notably heavy. High-temperature veins and skarns; notable: Panasqueira (Portugal), China, Mexico, Cornwall (England).
The geology.
Arsenopyrite carries the formula FeAsS. It belongs to the monoclinic (pseudo-orthorhombic) system. Catalogues list it as sulfide (arsenide).
It sits at 5.5 to 6 on the Mohs scale. The surface reads metallic, bright. Light behaviour is opaque. Specific gravity runs 6.0 to 6.2. The streak is dark gray to black. It breaks with distinct cleavage; uneven fracture; brittle.
Silver-white wedge-shaped metallic crystals, brighter and whiter than pyrite, striated and notably heavy.
It reaches buyers as wedge-shaped striated crystals, twinned crosses or massive ore.
The origins.
High-temperature veins and skarns; notable: Panasqueira (Portugal), China, Mexico, Cornwall (England).
On value, the database notes: affordable; sharp Portuguese crystals are collector pieces.
Traditional associations.
In energy work traditions, arsenopyrite has no lore; it is collected for its mirror-bright crystals and kept as a display-only piece.
We keep this section because people ask. It sits below the geology on purpose, and none of it describes something the stone does.
Spotting the real thing.
Silver-white wedge-shaped metallic crystals, brighter and whiter than pyrite, striated and notably heavy.
| Looks like | How to tell them apart |
|---|---|
| Pyrite | Pyrite is brass-yellow; arsenopyrite is silver-white |
| Marcasite | Marcasite is paler brass in cockscomb blades; arsenopyrite forms clean silver wedges |
| Galena | Galena is much softer and cleaves into cubes |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on arsenopyrite.
| Test | What you should see |
|---|---|
| By eye | Silver-white color with dark streak |
| By eye | Heavy (SG ~6.1) |
| By eye | Crushing or hard striking gives a garlic odor, do NOT test this deliberately |
If these checks leave you unsure, that is what appraisers are for. Do not file, heat or soak a piece to find out.
Care & handling.
At 5.5 to 6 on the Mohs scale it handles careful wear but scratches against quartz and dust. Store it separately and take rings off before rough work.
It breaks with distinct cleavage; uneven fracture; brittle, which is worth knowing before you set it or drop it.
Most damage happens during cleaning, not wearing. Avoid steamers, ultrasonic tanks and anything from under the sink.
Arsenic-bearing, stable as a specimen, but wash hands after handling, never grind, heat, or lick it, and keep it away from children.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is FeAsS. Crystal system: Monoclinic (pseudo-orthorhombic). Specific gravity: 6.0 to 6.2. Streak: Dark gray to black. Cleavage and fracture: Distinct cleavage; uneven fracture; brittle.
How it reaches the market
High-temperature veins and skarns; notable: Panasqueira (Portugal), China, Mexico, Cornwall (England).
What it gets confused with
Pyrite: Pyrite is brass-yellow; arsenopyrite is silver-white. Marcasite: Marcasite is paler brass in cockscomb blades; arsenopyrite forms clean silver wedges. Galena: Galena is much softer and cleaves into cubes.
What it is worth
Affordable; sharp Portuguese crystals are collector pieces.
One more thing
Arsenopyrite is the world's chief ore of arsenic, and a notorious troublemaker in gold mines, where it locks gold inside its crystals.
An education-first guide.
There is nothing to buy on this page. Arsenopyrite is not part of our catalogue, and the guide is here anyway because somebody searching the name deserves a straight answer.
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