Arsenolite
Chemical formula: As<sup>3+</sup><sub>2</sub>O<sub>3</sub>
Arsenolite is an arsenic oxide, a secondary arsenic mineral that forms small, colorless or white crystals with a cubic structure and adamantine luster.
Properties
- Mohs hardness
- 1.5
- Luster
- Vitreous, Silky, Adamantine
- Streak
- White
- Density
- 3.86
- Cleavage
- Imperfect on {111}
- Fracture
- Conchoidal to uneven
- Transparency
- Transparent to translucent
- Crystal system
- Isometric
Diagnostic features
## Identification Arsenolite is most easily recognized by its typical small, octahedral crystals with a cubic form. Its very low hardness (can be scratched with a fingernail), white color, vitreous or adamantine luster, and occurrence as an oxidation product of other arsenic minerals are key features. It often forms loose coatings or crusts. Due to its toxicity, taste tests are absolutely excluded. ## Distinguishing from Similar Minerals - **Claudetite:** It is a polymorph of arsenolite, but crystallizes in the monoclinic system, forming tabular or fibrous crystals. It also has perfect cleavage, which arsenolite lacks. - **Pharmacolite:** It is a hydrated calcium arsenate, forming silky, acicular or fibrous aggregates and crystallizing in the monoclinic system. It is also very soft. - **Halite (rock salt):** Forms cubic crystals, but has a salty taste and is significantly less dense. ## Crystal Forms Arsenolite crystallizes in the cubic system, most often forming perfectly developed, small octahedral crystals. Less commonly, cubic or rhombic dodecahedral forms are encountered. It also occurs as granular, earthy, powdery aggregates, as well as efflorescences and crusts.
Geological environment
## Genesis Arsenolite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits rich in arsenic, such as arsenopyrite, löllingite, realgar, or orpiment. It forms as a result of the exposure of these minerals to atmospheric oxygen. It can also form as a sublimation product from volcanic gases or as a result of underground fires in mines and on mine dumps. ## Mineral Associations It most often co-occurs with the minerals from which it forms, i.e., arsenopyrite, realgar, orpiment, as well as other secondary arsenic minerals like pharmacolite, erythrite, annabergite, or scorodite. Iron oxides (limonite) and quartz may also accompany it. ## Localities Significant arsenolite localities are found in many places around the world. Classic localities include: St Andreasberg mine in the Harz Mountains (Germany); Jáchymov and Příbram (Czech Republic); Sterling Hill mine in New Jersey (USA); Atacama region (Chile); as well as numerous localities in France, Italy (Sardinia), and Greece (Laurion).
Rarity
Not very common
For collectors
## Quality Criteria The most prized specimens by collectors are those with sharp, well-formed, and transparent octahedral crystals, clearly contrasting with the host rock (matrix). A contrasting matrix, for example with realgar or arsenopyrite, enhances its appeal. Crystal size is also important—specimens with crystals exceeding a few millimeters are considered exceptional. Purity (lack of impurities) and luster also affect value. ## Popular Localities Classic, highly valued specimens come from historical mines in St Andreasberg, Germany, and Jáchymov, Czech Republic. In recent years, attractive specimens from the Jiepaiyu mine in China have also appeared on the market, often in association with realgar.
Care and storage
## Cleaning Arsenolite is very soft, water-soluble, and highly toxic. Contact with water must be strictly avoided. Mechanical cleaning is inadvisable due to its brittleness and toxicity. The safest way to remove dust is with a soft brush or a stream of compressed air from a safe distance, always using personal protective equipment (gloves, mask). ## What to Avoid - **Water and moisture:** The mineral is water-soluble. Store in a dry place. - **Physical contact:** Avoid touching with bare hands due to toxicity. Wash hands thoroughly after any contact. - **Inhaling dust:** Arsenolite dust is extremely dangerous. Do not crush, heat, or perform any activities that could generate dust. - **High temperature:** It can sublimate (transition to a gaseous state) at elevated temperatures, releasing toxic arsenic fumes. ## Storage Arsenolite specimens must be stored in sealed, clearly labeled containers (e.g., "perky box" type), away from children, pets, and food. The container should be placed in a dry location, away from heat sources and direct sunlight. It is recommended to include a warning label about the mineral's toxicity.