Realgar

Realgar and Orpiment are both arsenic sulfides. Orpiment is a rare orange to lemon-yellow mineral consisting of a native trisulfide of arsenic and usually forms with Realgar. Realgar and Orpiment are almost always found together. Realgar is a bright reddish-orange arsenic sulfide. Crystals of orpiment are extremely rare as it usually forms masses and crusts, and may be crystallized in bright needles. (Realgar in this form is called ruby of arsenic). The yellow color is special to orpiment and can be confused only with a few other minerals. These two minerals are insoluble, but they do volatilize easily when heated. They release a strong garlic smell (arsenic). Realgar tends to turn to orpiment when exposed to sunlight. Over time, orpiment will deteriorate into a powder. The process takes a long time, but exposure to light will accelerate it. Specimens should be stored in dark, enclosed containers.

Both Orpiment and Realgar occur in low temperature hydrothermal veins which are fractures in rock where hot water precipitated minerals. They may also form in hot spring deposits and as sublimated gasses emitted from volcanoes.

In earlier days Arsenic was often called the “Poison of Kings” and was almost impossible to detect, but today, it can be detected with some basic chemical tests in a crime lab. Victorian era women used to ingest arsenic to make themselves look more “regally paler” to separate themselves from the tanned working class commoners.

Even though Orpiment and Realgar are arsenic compounds, they're not really hazardous in a rock collection. Don't taste the minerals, wash your hands after holding them, and you will have no problems.