Pararealgar
A variety of Minerals
What is Pararealgar?
Pararealgar is an arsenic sulfide mineral with the chemical formula As4S4 also represented as AsS. It forms gradually from realgar under exposure to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4. It is soft with a Mohs hardness of 1 - 1.5, is yellow orange in colour, and its monoclinic prismatic crystals are very brittle, easily crumbling to powder. It is one of the sulfides of arsenic and is one of two isomers of As4S4. It forms upon exposure of the symmetrical isomer to light. Its name derives from the fact that its elemental composition is identical to realgar, As4S4.
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Pararealgar before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Pararealgar Localities Map
See where Pararealgar is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Key Characteristics
Formation of Pararealgar
As stated above, pararealgar is an alteration product of realgar resulting from exposure to light. The process of alteration is dependent on the wavelength of light, with alteration only occurring at wavelengths longer than approximately 500 nm, in the visible light spectrum. In realgar's crystal structure, each arsenic atom is bonded to two sulphur atoms and one other arsenic atom. The As-As bonds are 30% weaker than the As-S bonds and certain wavelengths of lights interact with the crystal structure of realgar, breaking the weaker bonds between arsenic atoms. The free As formed as a result of this process destabilises the realgar structure, causing the realgar to become powdery pararealgar without changing overall chemical composition.
Composition of Pararealgar
Both isomers of As4S4 are molecular, in contrast to the other main sulfide of arsenic, orpiment (As2S3), which is polymeric. In pararealgar, there are three kinds of As centres (and three kinds of S centres). The molecule has Cs symmetry. In realgar, the four As (and four S) centres are equivalent and the molecule has D2d symmetry. An analogous pair of isomers is also recognized for the corresponding phosphorus sulfides P4S4.
Quick Facts
Physical Properties
- Color
- Light yellow to orange-brown
- Hardness (Mohs)
- 1 - 1.5
- Streak
- Light yellow
Chemical Properties
- Chemical Formula
- As4S4
- Elements
- As, S
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Pararealgar FAQs
How do I identify Pararealgar?
Pararealgar can be identified by its hardness of 1 - 1.5 on the Mohs scale, Light yellow to orange-brown color. Look for these key characteristics when examining specimens.
What color is Pararealgar?
Pararealgar typically appears in Light yellow to orange-brown. Color can vary depending on impurities and formation conditions.
How hard is Pararealgar?
Pararealgar has a hardness of 1 - 1.5 on the Mohs scale. This makes it a soft mineral that can be scratched easily.
What is the formation of pararealgar of Pararealgar?
As stated above, pararealgar is an alteration product of realgar resulting from exposure to light. The process of alteration is dependent on the wavelength of light, with alteration only occurring at wavelengths longer than approximately 500 nm, in the visible light spectrum. In realgar's crystal structure, each arsenic atom is bonded to two sulphur atoms and one other arsenic atom. The As-As bonds are 30% weaker than the As-S bonds and certain wavelengths of lights interact with the crystal structure of realgar, breaking the weaker bonds between arsenic atoms. The free As formed as a result of this process destabilises the realgar structure, causing the realgar to become powdery pararealgar without changing overall chemical composition.
What is the composition of pararealgar of Pararealgar?
Both isomers of As4S4 are molecular, in contrast to the other main sulfide of arsenic, orpiment (As2S3), which is polymeric. In pararealgar, there are three kinds of As centres (and three kinds of S centres). The molecule has Cs symmetry. In realgar, the four As (and four S) centres are equivalent and the molecule has D2d symmetry. An analogous pair of isomers is also recognized for the corresponding phosphorus sulfides P4S4.
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