Realgar is an historically important mineral, with a striking ruby-red color that stands out in the mineral kingdom. The rare transparent lustrous forms are truly masterpieces in mineral aesthetics.

Realgar is a photosensitive mineral and will alter to Pararealgar upon prolonged exposure to light. Pararealgar is unstable and will eventually crumble into a yellow powder if left in the light. The alteration mineral that Realgar transformed into was generally assumed to be Orpiment, but recent scientific analysis has in fact determined the orange alteration product as Pararealgar. Due to the instability of Realgar, specimens should be stored enclosed and covered to prevent their exposure to light. Occasional exposure to look at a specimen will not cause damage; only prolonged or repeated exposure will cause alteration. Several important museums have had Realgar on display consistently exposed to light, and these specimens can be seen altered and crumbled.

Realgar contains a significant amount of poisonous arsenic, and is itself somewhat toxic. Washing hands is recommended after handling Realgar specimens, especially if they are powdery.