Realgar, also known as “ruby sulfur” or “arsenic sulfide,” is a naturally occurring mineral composed of arsenic and sulfur with the chemical formula As₄S₄. It is classified as an arsenic sulfide mineral and is typically found in association with other minerals in hydrothermal veins and volcanic deposits. Realgar is known for its striking red to orange-red color and has been used historically as a pigment in dyes, as well as in traditional Chinese medicine.

Appearance: Realgar is transparent to translucent and typically occurs as tabular or prismatic crystals. It can also be found in grainy or massive forms.

Color: Its most distinctive feature is its bright red to orange-red color. This coloration is due to its arsenic content.

Uses: Realgar has been used for various purposes throughout history. In ancient times, it was used as a red pigment in paints and dyes, particularly in Chinese and Persian artworks. It was also employed in traditional Chinese medicine for its supposed therapeutic properties, although it is toxic and has limited medicinal use today.

Toxicity: Realgar is highly toxic due to its arsenic content. Ingesting or inhaling realgar can lead to arsenic poisoning, which can have severe health consequences. For this reason, its use in art and medicine has largely been replaced by safer alternatives.

Occurrence: Realgar is found in various locations around the world, including China, Russia, Romania, Peru, and the United States. It often forms in hydrothermal veins associated with other minerals like orpiment (another arsenic sulfide mineral), quartz, and cinnabar.

Safety: Handling realgar requires precautions due to its toxicity. It should not be ingested, inhaled, or placed in contact with the skin without adequate protection.

Historical Significance: Realgar has a long history of use in art and culture. In ancient China, it was used in paintings and as an ingredient in the production of fireworks. It was also associated with alchemy and was believed to have mystical properties.

Polymorphism & Series: Trimorphous with alacr´anite and pararealgar

Name: From the Arabic rahj al ghar for powder of the mine

Association: Orpiment, arsenolite, other arsenic minerals, calcite, barite

Crystallography: Monoclinic; prismatic. Found in short, vertically striated, prismatic crystals. Frequently coarse to fine granular and often earthy and as an incrustation.

Composition: Arsenic monosulfide, AsS. As = 70.1 percent, S = 29.9 percent.

Diagnostic Features: Realgar can be distinguished by its red color, resinous luster, and almost invariable association with orpiment. Its orange-red streak serves to distinguish it from other red minerals

While realgar has historical significance and interesting properties, its toxic nature has limited its use in contemporary applications. It is primarily of interest to mineral collectors and researchers studying mineralogical specimens.

Chemical Properties of Realgar

Chemical Classification Sulfide mineral
Chemical Composition As4S4 or AsS

Physical Properties of Realgar

Color Red to yellow-orange; in polished section, pale gray, with abundant yellow to red internal reflections
Streak Red-orange to red     
Luster Resinous to greasy
Cleavage Good on {010}; less so on {101}, {100}, {120}, and {110}
Diaphaneity Transparent
Mohs Hardness 1.5–2
Specific Gravity 3.56
Diagnostic Properties Toxic and carcinogenic.   Disintegrates on long exposure to light to a powder composed of pararealgar or arsenolite and orpiment.
Crystal System Monoclinic
Tenacity Sectile
Density 3.56 g/cm3 (Measured)    3.59 g/cm3 (Calculated)

Optical Properties of Realgar

Realgar optical PPL and XPL
Type Anisotropic
Color / Pleochroism Nearly colorless to pale golden yellow
Twinning Contact twins on {100}
Optic Sign Biaxial (-)
Birefringence δ = 0.166
Relief Very High

Realgar Occurrence and Formation

Realgar, also known as “ruby sulfur” or “arsenic sulfide,” occurs naturally in various geological settings. Its formation is closely tied to specific geological processes and environments. Here’s a closer look at the occurrence and formation of realgar:


  1. Hydrothermal Veins: Realgar is commonly found in hydrothermal vein deposits. These veins are created when hot, mineral-rich fluids circulate through fractures in rocks and then cool and deposit minerals as they come into contact with the surrounding rock. Realgar can precipitate from such hydrothermal fluids when conditions are right.
  2. Volcanic Environments: It can also be found in volcanic environments, often associated with fumaroles and hot springs. In these settings, realgar can form as a result of volcanic gases and hydrothermal activity.
  3. Sedimentary Rocks: Realgar may occasionally occur in sedimentary rocks, typically as a result of secondary processes. It can form as a result of the alteration of other arsenic minerals or the deposition of arsenic-bearing fluids.
  4. Associated Minerals: Realgar is often found in association with other minerals, including orpiment (another arsenic sulfide mineral), cinnabar (mercury sulfide), pyrite (iron sulfide), and various sulfides and sulfosalts.

Formation: The formation of realgar is a result of the interaction of arsenic and sulfur under specific geological conditions. Here’s a simplified explanation of how realgar forms:

  1. Source of Arsenic and Sulfur: Arsenic and sulfur must be present in the geological environment. These elements can be sourced from magmatic processes deep within the Earth’s crust or from other minerals containing arsenic and sulfur.
  2. Hydrothermal Activity: Hydrothermal fluids, which are typically hot, mineral-rich solutions, play a significant role. These fluids often originate from magma chambers deep underground and migrate through fractures and fissures in rocks.
  3. Precipitation: When these hydrothermal fluids encounter conditions that promote precipitation, such as a decrease in temperature or a change in pressure or chemical composition, the arsenic and sulfur components can combine to form realgar crystals.
  4. Cooling and Solidification: As the fluids cool and solidify, realgar crystals can grow within the fractures and cavities of the surrounding rock.
  5. Crystalline Growth: Realgar crystals can exhibit various habits, including tabular or prismatic forms, depending on the specific conditions during their growth.

It’s important to note that realgar formation is intricately tied to the geological history and local conditions of a given area. As a result, realgar can be found in diverse geological settings around the world, often in association with other minerals. However, its toxicity means that it should be handled with caution and not ingested, inhaled, or placed in contact with the skin without proper safety precautions.

Realgar Mining Sources and Distribution

Realgar, a mineral composed of arsenic and sulfur, is found in various locations around the world. Its mining sources and distribution are influenced by geological processes and the presence of specific mineral deposits. Here’s an overview of some of the regions where realgar is mined or has been found:

  1. China: China has historically been one of the most significant sources of realgar. It is particularly associated with regions such as Hunan, Guizhou, and Inner Mongolia. The Hunan province, in particular, has been a major producer of realgar for centuries. Realgar from China has been highly valued for its use in traditional Chinese medicine, as well as in art and cultural practices.
  2. Russia: Realgar deposits are also found in Russia, with notable occurrences in regions such as the Altai Mountains and the Far East. Russian realgar has been used in traditional medicine and occasionally in mineral collections.
  3. Peru: Peru has been another location where realgar has been mined. It is often associated with other minerals such as orpiment, cinnabar, and pyrite in mineral deposits. The occurrence of realgar in Peru has been of interest to mineral collectors.
  4. Romania: Romania has had occurrences of realgar, often found in association with other sulfide minerals. Mining activities in Romania have targeted various minerals, including realgar.
  5. United States: In the United States, realgar can be found in certain regions, although its occurrences are relatively limited compared to some other countries. There have been reports of realgar deposits in places like Nevada and Utah.
  6. Other Occurrences: Realgar can also be found in other countries, including Mexico, Morocco, Japan, and Italy, among others. However, its distribution is not widespread, and occurrences are often localized.

It’s important to note that realgar mining has declined over the years due to several factors:

  • Environmental Concerns: Realgar mining can have environmental impacts, and the toxicity of arsenic makes its handling and disposal a concern.
  • Health Risks: The health risks associated with handling realgar, as it contains toxic arsenic compounds, have led to a decrease in its use in traditional medicine and art.
  • Availability of Alternatives: Safer alternatives for pigments and medicinal purposes have largely replaced realgar in modern applications.

As a result of these factors, realgar mining is not as prevalent as it once was, and its use has become more limited and specialized. However, it remains of interest to mineral collectors and researchers studying mineralogical specimens.

Application and Uses Areas

The use of realgar (arsenic sulfide) has evolved over time, and its applications and uses have become more limited due to its toxic nature. Historically, realgar had various applications, but today, its uses are primarily restricted to niche areas. Here are some of the application and use areas of realgar:

  1. Traditional Chinese Medicine (TCM): Realgar has a long history of use in traditional Chinese medicine, where it is known as “Xionghuang” or “red arsenic.” It was used in small quantities in TCM formulations for its purported therapeutic properties, including its use in treating skin conditions, parasites, and as an antiseptic. However, due to its high toxicity, its use in TCM has decreased significantly, and safer alternatives are preferred.
  2. Art and Pigments: In ancient times, realgar was used as a red pigment in art and in the production of paints and dyes. It was particularly used in Chinese and Persian artworks for its vivid red color. However, its toxic nature and fading over time have led to the use of alternative, non-toxic pigments in modern art.
  3. Pyrotechnics: Realgar was used in the production of fireworks and pyrotechnics due to its ability to produce bright red flames when burned. However, safety concerns and the availability of safer chemicals have reduced its use in modern fireworks production.
  4. Mineral Collecting: Realgar, with its distinctive red color and crystalline forms, is of interest to mineral collectors and enthusiasts. Specimens of realgar are collected for display and study purposes.
  5. Research and Laboratory Use: Realgar can be used in laboratory research for its chemical properties. However, strict safety precautions are necessary when handling it due to its toxicity.

It’s important to emphasize that the toxic nature of realgar (arsenic compounds) poses significant health risks, and its use in many traditional and industrial applications has been largely replaced by safer alternatives. In many cases, the use of realgar has been discouraged or even prohibited due to health and environmental concerns.

Overall, while realgar has historical significance and certain niche applications, its use has diminished over time in favor of safer and more environmentally friendly alternatives. Users and collectors of realgar should exercise caution and follow safety guidelines to minimize exposure to its toxic properties.


  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • (2019). Handbook of Mineralogy. [online] Available at: [Accessed 4 Mar. 2019].
  • (2019). Realgar: Mineral information, data and localities.. [online] Available at: [Accessed 4 Mar. 2019].