What is Realgar?
Realgar is a vivid orange-red arsenic sulfide, a classic low-temperature hydrothermal mineral valued for colour and crystal form but requiring careful handling.
Mineralogy and crystal structure
Reference formula: As4S4. Realgar is monoclinic and is closely associated with orpiment. It can alter in light to yellow powdery pararealgar, so colour stability and storage conditions are part of specimen care. Realgar is classified with sulfides and has a monoclinic crystal system. Typical hardness is 1–2 on the Mohs scale and specific gravity is approximately 3.5–3.6.
Colour, lustre and habit
Typical colours include orange-red, scarlet, red-orange, yellow. The usual prismatic, granular, massive habit and resinous, vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Realgar forms in or is associated with low-temperature hydrothermal veins, volcanic fumaroles, hot springs and arsenic-rich ore deposits. Important documented localities include China, Romania, Peru, Switzerland, the United States, Japan and Central Asian localities.
A vivid red mineral with a serious chemistry
Realgar is one of the most visually effective small cabinet minerals: orange-red crystals stand out immediately, while the relationship with orpiment and light-driven alteration gives the specimen a scientific story.
Collecting and care
Keep sealed, cool, dark and dry. Do not cut, grind or heat; avoid dust and wash hands after handling arsenic-bearing specimens.
