Paradimorphite
Chemical formula: As<sub>4</sub>S<sub>3</sub>
Paradimorphite is a very rare arsenic sulfide, an orthorhombic, dimorphic variety of dimorphite.
Description
## Characteristics Paradimorphite is an arsenic sulfide and represents one of two crystalline forms (dimorph) of the compound As₄S₃. It forms very small, acicular or prismatic crystals, rarely exceeding a few millimeters in length. They usually occur as coatings and aggregates in rock cavities. It is a brittle mineral. ## Physical Properties Crystals are transparent to translucent and exhibit a strong, adamantine luster. The Mohs hardness is approximately 1.5, making it a very soft mineral. Its density is about 3.58 g/cm³. ## Colors and Varieties This mineral ranges in color from light yellow to orange-yellow. No color varieties or commercial varieties are known. ## History and Name Paradimorphite was first described in 1862 by Scacchi. Its name refers to its relationship with dimorphite – it is its polymorphic variety (from Greek *para* - beside, near). Both minerals have the same chemical composition but differ in crystallographic system. The type locality is Solfatara di Pozzuoli in Italy.
Diagnostic features
## Identification Identification of paradimorphite is primarily based on its specific occurrence environment (volcanic fumaroles), characteristic yellow color, adamantine luster, and acicular crystal habit. Due to the small size of the crystals, magnification is usually necessary for observation. ## Distinguishing from similar minerals The biggest challenge is distinguishing paradimorphite from its monoclinic dimorph – dimorphite. They have identical chemical compositions and very similar appearances. Definitive differentiation is possible almost exclusively using advanced analytical methods, such as X-ray diffraction (XRD). It can also be confused with orpiment, which, however, crystallizes in a different system, has perfect cleavage, and often forms larger, platy aggregates. ## Crystal forms Paradimorphite forms small, elongated crystals with a prismatic or acicular habit. They often occur as radial aggregates or disordered clusters growing on rock surfaces.
Geological environment
## Genesis Paradimorphite is a mineral of volcanic origin. It forms as a result of low-temperature sublimation from volcanic gases (exhalations) in active fumaroles. It crystallizes directly from the gas phase on cooler rock surfaces. ## Mineral associations This mineral almost always occurs in association with its dimorph – dimorphite. It also co-occurs with native sulfur, and less frequently with realgar and other arsenic sulfides. ## Localities The most important and classic locality for paradimorphite is its type locality – Solfatara crater in Pozzuoli, near Naples, Italy. It has also been reported from the Alacrán mine in Chile and several other volcanic localities worldwide, but it is a very rare mineral everywhere.
Rarity
Very rare
Collector aspects
## Quality criteria In the case of such a rare mineral, the main criterion for value is the mere presence of well-formed, identifiable crystals. Specimens with distinct, unaltered crystals of intense color and strong luster are most highly valued. The richness of the aggregate and association with other rare fumarolic minerals, especially dimorphite, are also of great importance. ## Popular localities The vast majority of collector specimens come from the type locality in Italy (Solfatara di Pozzuoli). Material from other localities is extremely rare on the market.
Care and storage
## Cleaning Paradimorphite specimens are extremely delicate and sensitive. Cleaning should be kept to an absolute minimum. Only very careful dust removal with a soft brush or a stream of compressed air from a distance is permissible. ## What to avoid Contact with water and all chemicals must be strictly avoided. Paradimorphite is sensitive to light, which can cause its slow decomposition and loss of color and luster. It should also be protected from high temperatures and humidity. Due to its arsenic content, hands should be thoroughly washed after each contact with the mineral. ## Storage Storage requires special conditions. Specimens should be kept in tightly sealed, opaque containers or boxes, in a dry, cool, and completely dark place. The best solution is storage in "micromount" type system boxes.