Orpiment

Orpiment is an arsenic sulfide mineral (As₂S₃), the golden-yellow companion to its red relative realgar. Orpiment forms in the same geological environments as realgar: low-temperature hydrothermal veins, hot springs, and volcanic fumaroles. It's the arsenic trisulfide to realgar's arsenic tetrasulfide. Where you find one, you almost always find the other.

Orpiment's perfect basal cleavage produces thin, flexible sheets with a pearly luster on the cleavage surface. This property, combined with its brilliant golden-yellow color, made it historically important as a pigment. The name 'orpiment' comes from the Latin 'auripigmentum' (gold pigment). Ancient Roman and Egyptian artists used it despite its toxicity.

Alchermists called orpiment 'king's yellow' and valued it for its resemblance to gold. They believed the arsenic sulfides were close to gold in nature's hierarchy of matter, leading to extensive (and dangerous) experiments attempting to transform them into actual gold.

Orpiment is identified by its vivid lemon to golden-yellow color, very low hardness (1.5), perfect cleavage producing flexible sheets, and pearly luster on cleavage surfaces. The combination of yellow color and extreme softness narrows identification significantly.

Distinguish from sulfur (lighter yellow, different crystal habit, melts easily), yellow calcite (much harder, effervesces in acid), and gold (metallic luster, much heavier, malleable). SAFETY: Contains arsenic. Handle carefully and wash hands after.