Alacránite
Chemical formula: As<sub>8</sub>S<sub>9</sub>
Alacranite is a rare arsenic sulfide, forming orange-yellow crystals and aggregates, unstable under light.
Description
## Characteristics Alacranite is an arsenic sulfide that forms small, tabular or prismatic crystals, often with a pseudo-octahedral appearance. It usually occurs as fine-grained, massive, or earthy aggregates. Its most characteristic feature is an intense, orange-yellow to yellow color, sometimes with a reddish tint. It is a brittle mineral. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 1.5-2, meaning it can be scratched with a fingernail. The luster is resinous to greasy. It is translucent, and in thicker fragments, opaque. Its density is approximately 3.43 g/cm³. ## Colors and Varieties The typical color of alacranite is intense orange-yellow. Depending on impurities and formation conditions, it can take on shades from lemon-yellow to reddish-orange. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from its first discovery location – the Alacrán mine in Copiapó Province, Atacama Region, Chile. It was described and approved as a new mineral species by the International Mineralogical Association in 1980. ## Uses Alacranite has no industrial applications. Due to its rarity, intense color, and interesting associations, it is a valued and sought-after collector's mineral.
Diagnostic features
## Identification Key diagnostic features include its orange-yellow color, very low hardness (can be scratched with a fingernail), and resinous luster. Its instability in light, leading to a change in color to a more yellow hue, is also an important, though destructive, clue. ## Distinguishing from Similar Minerals Alacranite can be confused with realgar, which is usually redder and crystallizes in the monoclinic system. It is more difficult to distinguish it from pararealgar and orpiment, which have a lighter, lemon-yellow color. Certain differentiation, especially from pararealgar, often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms small, tabular or short-prismatic crystals, often exhibiting a pseudo-octahedral habit. It is most commonly found as fine-grained, massive, or earthy aggregates and coatings.
Geological environment
## Genesis Alacranite is a mineral of low-temperature hydrothermal processes. It often forms as a product of secondary alteration of other arsenic minerals, mainly realgar, under the influence of light or chemical changes. It is also found as a product of volcanic sublimation and in hot spring deposits. ## Mineral Associations It co-occurs with other arsenic sulfides, such as realgar, orpiment, uzonite, and duranusite. It is often accompanied by native arsenic, native sulfur, and various mercury minerals. ## Localities The most important localities worldwide include the Alacrán mine in Chile (type locality), the Pobeda deposit in Yakutia (Russia), the Getchell mine in Nevada and the Lookout Pass deposit in Utah (USA), and the locality of Jas Roux in the Hautes-Alpes (France).
Rarity
Rare
Collector aspects
## Quality Criteria Specimens with well-formed, sharp crystals of intense, orange color are most highly valued. Due to the small size of the crystals, even small but well-formed groups on a rock matrix are highly desirable. Association with other rare minerals, such as realgar or uzonite, is also important. ## Popular Localities Specimens of the best crystalline quality, forming distinct crystals, mainly come from the Getchell mine in Nevada (USA) and the Pobeda deposit in Russia. Chilean specimens from the type locality are mainly of historical significance.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft brush or compressed air. Do not use water, ultrasonic cleaners, or any chemical agents that could damage or alter the mineral. ## What to Avoid Alacranite is very unstable under light – even brief exposure to sunlight or strong artificial light causes its decomposition and transformation into other, more stable arsenic sulfides (e.g., pararealgar). The mineral is toxic due to its arsenic content – avoid inhaling dust and always wash hands after contact. It should not be heated. ## Storage Alacranite specimens must be stored in complete darkness, preferably in closed, opaque boxes. Any exposure to light should be limited to an absolute minimum to prevent its degradation.