Realgar is the principle ore for arsenic, and so it is quite dangerous.

Chemical Formula: AsS
Class: Arsenic Sulfides
Hardness: 1.5-2
Coloration: Red

How to identify it/Unique Characteristics or Properties: Realgar is the principle ore for arsenic, and so is quite dangerous. Realgar is a bright red when it comes out, but quickly degrades in sunlight, becoming orpiment or pararealgar. In the image below, you can see some realgar left in back but most has degraded to orpiment.

Where to find it in…

The Northwest: Washington
Other: Germany, Mexico, Corsica, Romania, Nevada/Utah
Past Uses: Realgar has been carved, and used in pigments for paintings. However, over time the color degrades to yellow. It was also used in fireworks for the red color, but that has stopped because of the arsenic.
How it was Made: Realgar is found in hydrothermal vents and hot springs, or condenses from volcanic gas.
Interesting Facts: Realgar smells of garlic due to the arsenic, and rarely forms crystals.