Pararealgar is the alteration product of the mineral Realgar. It forms when Realgar is exposed to light, which causes a physical change in the structure of the mineral and transforms it into a new mineral. Pararealgar is has the same chemical composition and chemical formula as Realgar, but its crystal form differs. Pararealgar is also different in color than Realgar; whereas Realgar is bright red, Pararealgar is bright orange or yellow, and additionally has a more powdery consistency.

Pararealgar is usually associated with Realgar, and specimens can be partially altered. It is not uncommon for specimens to be only partially altered in sections, creating yellow and red color zones. Once a significant alteration has taken place, the mineral will start to crumble. 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. Pararealgar, like Realgar, is photosensitive, and will become unstable and eventually crumble into a yellow powder if left in the light. Specimens should be stored enclosed and covered to prevent their exposure to light.

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