sulfides
Realgar
AsS
- Also known as
- ruby sulphurarsenic blende
- Crystal system
- monoclinic
- Hardness
- 1.5–2 on the Mohs scale
- Lustre
- resinous
- Colour
- Orange-red to scarlet
- Where it forms
- In low-temperature hydrothermal veins and around hot springs, usually alongside orpiment.
- Chiefly from
- Hunan, ChinaRomaniaNevada, United StatesPeru
Why it is that colour
The arsenic sulfide compound itself.
Safety
Arsenic sulfide. Very soft, easily abraded, and toxic. It also degrades in light: exposed to sunlight over months, realgar crumbles to a yellow powder called pararealgar, so a specimen left on a windowsill is actively shedding arsenic dust. Keep it in the dark, handle it as little as possible, wash your hands, and never powder or ingest it.
Where it comes from
Chinese and Peruvian specimen material. Not mined at scale any more.
Historical use
A pigment, and a poison. Realgar was used to kill rats and flies, and in dye and fireworks for its brilliant colour. Its degradation is a genuine problem for conservators, since paintings using it have faded in ways that misrepresent the artist’s intent.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
Used as a pigment and, alarmingly, in traditional medicine in several traditions. The name comes from Arabic rahj al-ghar, powder of the mine. Arsenic preparations appear in medieval European and in Chinese pharmacopoeias; arsenic poisoning from the latter is documented in modern case reports.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Worth knowing
Realgar is unstable in a way that makes it actively hazardous to keep. Light converts it, over months to years, into pararealgar — a yellow powder with the same chemistry and a different structure — and the conversion breaks the crystal apart. A realgar specimen displayed in daylight is slowly turning into arsenic-bearing dust on the shelf it stands on.
Mineral collectors know this and store it in the dark. It is sold in wellbeing shops as a bright orange curiosity, generally without the storage advice, which is a small illustration of what the two markets know about the same object.
Identity checked against IMA-CNMNC master list, June 2025.