Orpiment is one of the more common arsenic ores.

Chemical Formula: As2S3
Class: Arsenic Sulfides
Hardness: 1.5-2
Coloration: Yellow

How to identify it/Unique Characteristics or Properties: Orpiment is one of the more common arsenic ores. It has very small crystals and turns to powder very easily. Like realgar, it deteriorates in the sun. When realgar breaks down it also sometimes breaks down into orpiment, like the picture below.

Where to find it in…

The Northwest: Utah
Other: Russia, Germany, Peru, Turkey, Japan
Past Uses: Orpiment is used to gather arsenic, and is so was used as a poison, but due to its yellow color, it was also used as a yellow dye and in cosmetics until people realized how dangerous arsenic was.
How it was Made: Orpiment is found in hydrothermal vents or condenses from volcanic gas, sometimes forming a crust over other minerals.
Interesting Facts: Orpiment smells of garlic and it is thought that the use of this mineral as pigment for wallpaper is what cause Napoleon’s death by long term arsenic poisoning, as the wallpaper got wet through humidity and released small doses of arsenic into the air.