Pararealgar

Chemical formula: AsS

Pararealgar is an arsenic sulfide, a polymorphic variety of realgar, formed by its transformation under the influence of light.

## Characteristics Pararealgar is an arsenic sulfide that most often forms as a product of realgar's transformation upon exposure to light. It usually occurs as fine-grained, earthy, or powdery coatings and aggregates on the surface of realgar crystals. It rarely forms its own microscopic, prismatic crystals. Its presence is a signal that the primary, red realgar has degraded, changing its crystal structure and properties. ## Physical Properties Pararealgar is a very soft mineral, with a Mohs hardness of 1-1.5. It has a resinous to greasy luster. It is a brittle mineral, and its density is approximately 3.52 g/cm³. Due to its occurrence as coatings, many of its physical properties are difficult to observe in typical specimens. ## Colors and Varieties It is characterized by an intense, orange-yellow or lemon-yellow color, which strongly contrasts with the red color of the realgar on which it forms. No distinct color varieties or commercial forms are recognized. ## History and Name The name "pararealgar" refers to its close relationship with realgar and was approved by the International Mineralogical Association (IMA) in 1980. It was described based on material from the Getchell mine in Humboldt County, Nevada (USA), and from the Lukhumi mine in Georgia. Its formation as a product of realgar's photochemical transformation had been observed earlier, but it was only formally recognized as a distinct mineral species in 1980. ## Applications Pararealgar has no industrial applications. Its significance is purely scientific and collectible, as an indicator of mineral transformation processes and an interesting example of polymorphism.

Properties

Mohs hardness: 1-1.5
Color: Light yellow to orange-brown
Luster: Vitreous/Resinous
Streak: Light yellow
Density: 3.52
Cleavage: Good on {100}
Fracture: Irregular/Uneven
Transparency: Translucent,Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Pararealgar is most easily recognized by its characteristic orange-yellow color and form of occurrence – as a powdery or earthy coating on red realgar crystals. It is a typical product of its decomposition under the influence of light. ## Distinguishing from Similar Minerals It can be confused with orpiment, which is also a yellow arsenic sulfide and often co-occurs with realgar. However, orpiment usually has a more golden-yellow hue and often forms more distinct, platy crystals. Pararealgar is an intermediate stage in the transformation of realgar into orpiment, hence their close proximity. ## Crystal Forms It most often occurs in the form of dusty, earthy, or crusty coatings. Very rarely, it forms well-developed, microscopic (up to 1 mm) crystals with a short prismatic habit.

Geological environment

## Genesis Pararealgar is a secondary mineral, formed exclusively as a result of the photochemical transformation of realgar (α-AsS). This process occurs under the influence of visible light exposure. It is an example of polymorphism, where a mineral with the same chemical composition (AsS) changes its crystal structure. It occurs in the same environments as realgar, i.e., in low-temperature hydrothermal veins, in volcanic deposits (fumaroles), and in some hot spring deposits. ## Mineral Associations It always occurs in association with realgar, from which it forms. It often co-occurs with orpiment (being the final product of the transformation), calcite, barite, and other arsenic sulfides. ## Localities Significant occurrences of pararealgar have been reported in many places worldwide where realgar is found. Key localities include the Getchell mine in Nevada and the Mercur deposit in Utah (USA), the Shimen deposit in Hunan Province (China), the Lukhumi mine in Georgia, the Baia Sprie deposit in Romania, and the Allchar deposit in North Macedonia.

Rarity

Not very common

For collectors

## Quality Criteria The quality of a pararealgar specimen is inextricably linked to the quality of the primary realgar specimen. The most valued samples are those where partial transformation is visible – well-formed, red realgar crystals covered with a contrasting, yellow coating of pararealgar. Such a specimen serves as an interesting document of the mineralogical transformation process. Pure aggregates of pararealgar itself have less visual and collectible value. ## Popular Localities Among the most famous localities from which pararealgar specimens originate are the Getchell mine in Nevada (USA), where it was first described in detail, and the Shimen deposit in China, known for large and spectacular realgar crystals that often undergo transformation.

Care and storage

## Cleaning Specimens with pararealgar should generally not be wet-cleaned. Any contaminants, such as dust, should be removed only dry, using a soft brush or a photographic air blower. Contact with water can damage delicate coatings. ## What to Avoid The most important destructive factor is light, especially sunlight, which initiates and accelerates the transformation of realgar into pararealgar, and then into orpiment. Specimens should be protected from all chemicals, high temperatures, and humidity. The mineral is toxic due to its arsenic content – avoid inhaling dust and wash hands after any contact. ## Storage Specimens with pararealgar and realgar require storage in complete darkness, preferably in tightly sealed, opaque boxes or cabinets. Display is not recommended, as even artificial lighting will eventually lead to further degradation of the mineral.