Comparison · Minerals vs Sulfide Minerals
Arsenopyrite vs Marcasite
Arsenopyrite and Marcasite are easy to confuse. Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Arsenopyrite and Marcasite
- Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Arsenopyrite leaves a dark grayish black streak on unglazed porcelain, Marcasite leaves dark greenish gray to brownish black.
- Both look metallic, so compare color, tarnish and weight rather than shine.
- Arsenopyrite feels noticeably heavier for its size (specific gravity 6.0–6.2 versus 4.9 for Marcasite).
- Hold a thin edge to the light: Arsenopyrite is Opaque, Marcasite is opaque.
- They overlap in white and yellow, but Arsenopyrite also comes in gray and multicolored and Marcasite also comes in brown.
- Well-formed crystals give it away: Arsenopyrite is Monoclinic, Marcasite is orthorhombic.
Arsenopyrite vs Marcasite properties
| Property | Arsenopyrite | Marcasite |
|---|---|---|
| Type | Minerals | Sulfide Minerals |
| Mohs hardness | 5.5–6 | 6 |
| Luster | Metallic | metallic |
| Streak | Dark grayish black | Dark greenish gray to brownish black |
| Transparency | Opaque | opaque |
| Specific gravity | 6.0–6.2 | 4.9 |
| Crystal system | Monoclinic | orthorhombic |
| Common colors | Silver-white, Steel-gray, Tarnished yellowish/iridescent | Pale brass yellow, Tin white, Bronze |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $5–$200+ |
Which is more valuable?
Marcasite is usually the more valuable of the two: a typical collector specimen runs about $35 against $20 for Arsenopyrite, and premium Marcasite can reach $200 or more.
About Arsenopyrite
Arsenopyrite is an iron arsenic sulfide, FeAsS, and the most common arsenic-bearing mineral in Earth's crust. It crystallizes in the monoclinic system despite forming crystals that often look nearly orthorhombic, and it stands as the primary ore of arsenic. Its silvery, metallic luster and tendency to tarnish to a dull gray or iridescent surface distinguish it at a glance from ordinary pyrite.
About Marcasite
Marcasite is an iron sulfide mineral with the same composition as pyrite but a different crystal structure. It appears as pale brass-yellow crystals, radiating groups, and botryoidal masses, and is prone to crumbling as it oxidizes over time.
Arsenopyrite vs Marcasite FAQ
Is Arsenopyrite the same as Marcasite?
No. Arsenopyrite is a mineral while Marcasite is a sulfide mineral. Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Arsenopyrite from Marcasite?
Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Arsenopyrite leaves a dark grayish black streak on unglazed porcelain, Marcasite leaves dark greenish gray to brownish black. Both look metallic, so compare color, tarnish and weight rather than shine.
Which is harder, Arsenopyrite or Marcasite?
They are about equally hard, both near Mohs 5.5–6.
Which is more valuable, Arsenopyrite or Marcasite?
Marcasite is usually the more valuable of the two: a typical collector specimen runs about $35 against $20 for Arsenopyrite, and premium Marcasite can reach $200 or more.
