Identification guide · Sulfide Minerals
How to Identify Orpiment
Orpiment is usually lemon yellow, golden yellow, and orange-yellow with a resinous luster and is translucent. It has a Mohs hardness of 1.75. A fingernail (Mohs 2.5) scratches it easily. Its streak is pale lemon yellow. It is most often confused with Realgar, Vanadinite, and Amber; the tests below separate them.
Orpiment identification checklist
| Color | Lemon yellow, Golden yellow, Orange-yellow, Brownish yellow | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Resinous | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 1.75 | A fingernail (Mohs 2.5) scratches it easily. |
| Streak | Pale lemon yellow | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect on {010} | |
| Fracture | Uneven | |
| Specific gravity | 3.49 | Heavier than it looks (specific gravity about 3.49). |
| Crystal system | Monoclinic |
Orpiment look-alikes and how to tell them apart
Both sit near Mohs 1.75, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Orpiment vs Realgar →
Vanadinite is harder (Mohs 3) than Orpiment (Mohs 1.75), so Vanadinite will scratch Orpiment and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Orpiment vs Vanadinite →
Both sit near Mohs 1.75, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Orpiment vs Amber →
Calcite is harder (Mohs 3) than Orpiment (Mohs 1.75), so Calcite will scratch Orpiment and not the other way round. A fingernail (Mohs 2.5) scratches it easily.
Field tips
- Look for a soft, bright lemon to golden-yellow mineral with a resinous to pearly luster.
- Orpiment is very soft at about 1.5 to 2 and has one perfect cleavage that yields flexible flakes.
- Its pale yellow streak and association with red-orange realgar are strong identifying clues.
Orpiment identification FAQ
How can you tell if a rock is Orpiment?
Check the color (lemon yellow, golden yellow, orange-yellow, and brownish yellow), the resinous luster, a Mohs hardness of 1.75 and a pale lemon yellow streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Orpiment?
Orpiment has a Mohs hardness of 1.75. A fingernail (Mohs 2.5) scratches it easily.
What is the difference between Orpiment and Realgar?
Orpiment (Mohs 1.75, resinous luster) and Realgar (Mohs 1.75, resinous luster) look alike, but hardness, streak and heft usually separate them. See the full Orpiment vs Realgar comparison for a side-by-side table.
Is Orpiment worth anything?
Entry-level Orpiment specimens sell for around $10, typical collector pieces about $60, and premium examples $400 or more depending on size, quality and locality.
What color is Orpiment?
Orpiment is most often lemon yellow, golden yellow, orange-yellow, and brownish yellow. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
