Identification guide · Minerals
How to Identify Arsenopyrite
Arsenopyrite shows a bright silvery-white to steel-gray color with a metallic luster that can tarnish to a dull, sometimes iridescent surface. Its streak is dark gray to black, hardness falls around 5.5 to 6, and it lacks a strong cleavage, instead breaking with an uneven fracture. Crystals are typically elongated, striated prisms with a diamond-shaped cross section. It is commonly confused with pyrite and marcasite, but arsenopyrite is denser, may give off a garlic-like odor when struck, and its crystal shape is more elongated than pyrite's cubes.
Arsenopyrite identification checklist
| Color | Silver-white, Steel-gray, Tarnished yellowish/iridescent | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Metallic | Turn it under a lamp: a true metallic shine reflects like polished metal and stays opaque at thin edges. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5.5–6 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Streak | Dark grayish black | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Distinct on {110} | |
| Fracture | Uneven to subconchoidal, brittle | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 6.0–6.2 | Very heavy, metallic heft (specific gravity about 6.1). |
| Crystal system | Monoclinic |
Arsenopyrite look-alikes and how to tell them apart
Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Arsenopyrite vs Pyrite →
Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Arsenopyrite vs Marcasite →
Arsenopyrite is harder (Mohs 5.5–6) than Bismuth (Mohs 2–2.5), so Arsenopyrite will scratch Bismuth and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Arsenopyrite vs Bismuth →
Both sit near Mohs 5.5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Arsenopyrite vs Cobaltite →
Arsenopyrite identification FAQ
How can you tell if a rock is Arsenopyrite?
Check the color (silver-white, steel-gray, and tarnished yellowish/iridescent), the metallic luster, a Mohs hardness of 5.5–6 and a dark grayish black streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Arsenopyrite?
Arsenopyrite has a Mohs hardness of 5.5–6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is the difference between Arsenopyrite and Pyrite?
Arsenopyrite (Mohs 5.5–6, metallic luster) and Pyrite (Mohs 6.5, metallic luster) look alike, but hardness, streak and heft usually separate them. See the full Arsenopyrite vs Pyrite comparison for a side-by-side table.
Is Arsenopyrite worth anything?
Entry-level Arsenopyrite specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Arsenopyrite?
Arsenopyrite is most often silver-white, steel-gray, and tarnished yellowish/iridescent. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
