Realgar

Realgar is a soft orange-red arsenic sulfide mineral with formula As₄S₄. It occurs naturally and has been used as a pigment and in fireworks.

Arsenic sulfide: A family of compounds formed from arsenic and sulfur, including several naturally occurring minerals. Realgar is one member of this chemically defined family.
Realgar photodegradation: The light-driven transformation of realgar into other arsenic sulfide phases, especially pararealgar. This process accounts for realgar’s fading and color change in exposed specimens.
Realgar pigment: A red-orange pigment made from ground realgar, used historically in painting and decoration. Its intense hue explains realgar’s long-standing use as a colorant.
Arsenic toxicity: The harmful effects of arsenic exposure, which can damage multiple organs and cause cancer. Realgar’s arsenic content makes handling and dust exposure hazardous.
Orpiment: A yellow arsenic sulfide mineral with formula As₂S₃. It commonly occurs with realgar and shares its arsenic-sulfide chemistry.
Pararealgar formation: The conversion of realgar into pararealgar through exposure to light and associated chemical changes. It is the characteristic alteration pathway that makes realgar unstable in light.
Chinese fireworks: Pyrotechnic devices developed in China using gunpowder and other combustible materials. Realgar has been used in some traditional firework compositions to produce color effects.
Mineral dust: Fine particles released from minerals through crushing, abrasion, or weathering. Dust from realgar can expose people to toxic arsenic compounds.
Pararealgar: A yellow-orange arsenic sulfide mineral formed when realgar is altered by light. Its formation helps explain why exposed realgar can change color and mineral identity.
Arsenic trioxide: An inorganic arsenic compound with formula As₂O₃, occurring naturally as arsenolite and claudetite. Oxidative weathering of arsenic minerals can produce this toxic compound.

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