Crystal Structure
Monoclinic As₄S₄ — As₄ cage molecules linked.
Elemental Composition (by mass)
| Element | Mass % | Visual |
|---|---|---|
| As Arsenic | 70.03% | |
| S Sulfur | 29.97% |
Computed from simplified end-member formula. Solid-solution series, water content, and trace substitutions cause real-world variation.
IMA Abbreviation (Whitney-Evans 2010)
Rlg
→ Realgar
As sulfide
Standard symbol from American Mineralogist (Whitney & Evans, 2010). Used in thin-section labeling, phase diagrams, and IMA-style species records.
⏳ Long-term Aging & Care Timeline
photodecomposition to pararealgarweeks to months
Trigger: visible light + UV
Intervention: Store dark; use UV-filter case. Color shift orange→yellow→powder. Reversible only in early stage.
Pronunciation
/riˈælɡɑːr/
↔ ree-AL-gar
Arabic rahj al-ghar
⚠ Safety & Handling
☠toxichigh
Arsenic sulfide — As releases via abrasion and ingestion. Dust inhalation especially dangerous.
Handling: No skin contact recommended. Wash hands. Keep dust off food prep surfaces.
☼light-sensitivehigh
Realgar disintegrates in sunlight to pararealgar (orange-yellow powder) over weeks-months.
Handling: Store in dark drawer. Use UV-filtering display case if exposed. Document baseline color.
Information provided in good faith. Consult local hazmat regulations for transport and disposal. Severely hazardous specimens may require special storage cabinets.
Luster
resinous
Bright red-orange resinous.
Diaphaneity (Transparency)
translucent
Bright red translucent crystals.
Type Locality
(ancient Arabic "rahj al ghar") — Hungary
Source: Avicenna
› Browse all type localities
Diagnostic Field Tests
Light test→ Disintegrates in sunlight
Store in dark; turns to pararealgar (yellow-orange) over time.
Hot needle→ Pungent garlic/As₂O₃ smell
Toxic — use ventilation. Confirms As content.
⚠ Use dilute HCl (~10%) only on inconspicuous spots; rinse promptly. Smell-tests should be brief and ventilated. Taste-test ONLY halite/sylvite — never lead, arsenic, or sulfur minerals.
Streak Test
orange-red
Brighter orange than cinnabar.
Streak = color of the powdered mineral. Drag specimen across unglazed white porcelain plate (Mohs 6.5). For minerals harder than the plate, crush a small flake into powder and observe color.
Geological Setting
Environment:
hydrothermal
Host rock:
low-temp hydrothermal, hot-spring
Companions:
Always with orpiment; light-sensitive — degrades to pararealgar.
Care notesStore in dark; light decomposes it to pararealgar (yellow powder). Wash hands after handling — arsenic. Full cleaning guide →
Formation eraLow-T hydrothermal / fumarolic; Romanian specimens Mesozoic.
Cleavage & Fracture
Cleavage:
good 1 good {010}
Fracture:
conchoidal
Cleaves easily; light-sensitive surface.
Market availability: Rare
Sought after; limited supply. Major shows and specialist dealers only.
Collector tier: Solid Display
Reliable mid-tier display species. Easy to find in well-formed examples; broad locality diversity.
PolymorphsShares the formula
AsS with: Pararealgar — same chemistry, different crystal structure.Mohs 1.5–2
Vickers (~) 75 HV
Knoop (~) 85 HK
Nickel–Strunz
2.FA.15aDana
02.13.06.01Geological setting
VolcanicHydrothermal
Element composition by mass
Formula: As₄S₄ · molar mass: 427.93 g/mol
| As | 70.03% | |
| S | 29.97% |
Computed from atomic weights (IUPAC 2021). Site-occupancy groups (Fe,Mn) split equally.
Mohs Hardness
1.5–2
Realgar sits at 1.5–2 on the Mohs scale — soft enough to be scratched by a fingernail.
Colors:
Streak
Orange-yellow
Orange-yellow
Crystal system
Monoclinic
Monoclinic
Pronunciation/riːˈælɡɑːr/
Type localityMatra mine, Corsica, France
Sulfides & SulfosaltsSulfides
TL;DR · 1 min read
Realgar (As₄S₄) is a vivid red-orange arsenic sulfide that crystallizes from low-temperature hydrothermal and volcanic fumarolic systems. It forms paired with orpiment (As₂S₃) — together they are known as the "ruby and gold of arsenic minerals.
Realgar (As₄S₄) is a vivid red-orange arsenic sulfide that crystallizes from low-temperature hydrothermal and volcanic fumarolic systems. It forms paired with orpiment (As₂S₃) — together they are known as the “ruby and gold of arsenic minerals.” China’s Tengchong volcanic field (Yunnan) and Shimen mining district (Hunan) are the country’s two principal sources.
Notable Chinese Localities
Tengchong volcanic field (Yunnan) yields vivid red prismatic crystals from active fumaroles. The Shimen Realgar Mine (Hunan) produced the world’s largest realgar specimens during the late 20th century, including museum pieces over 30 cm.
Cite this entry
APA
MyMineralBox Editorial Team. (2026). Realgar. My Mineral Box. Retrieved May 23, 2026, from https://mymineralbox.com/mineral-encyclopedia/minerals/realgar/
MLA
MyMineralBox Editorial Team. "Realgar." My Mineral Box, 2026, https://mymineralbox.com/mineral-encyclopedia/minerals/realgar/. Accessed May 23, 2026.
Chicago
MyMineralBox Editorial Team. "Realgar." My Mineral Box. Last modified May 4, 2026. https://mymineralbox.com/mineral-encyclopedia/minerals/realgar/.
BibTeX
@misc{mmb_realgar,
author = {{MyMineralBox Editorial Team}},
title = {{Realgar}},
year = {2026},
publisher = {My Mineral Box},
url = {https://mymineralbox.com/mineral-encyclopedia/minerals/realgar/},
urldate = {2026-05-23}
}