Hutchinsonite
Chemical formula: Pb<sup>2+</sup>Tl<sup>1+</sup>As<sup>3+</sup><sub>5</sub>S<sup>2-</sup><sub>9</sub>
A rare lead, thallium, and arsenic sulfide, prized for its intensely red, prismatic crystals and adamantine luster.
Properties
- Mohs hardness
- 1.5-2
- Luster
- Adamantine to Sub-Metallic
- Streak
- Cherry red
- Density
- 4.6
- Cleavage
- Good on {010}
- Fracture
- Sub-Conchoidal to Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Key diagnostic features of hutchinsonite include its characteristic carmine-red color, very strong adamantine or metallic luster, low hardness (1.5-2 on the Mohs scale), and cherry-red streak. Its occurrence in association with other arsenic and thallium sulfosalts, such as realgar or orpiment, is also a strong indicator. ## Distinguishing from Similar Minerals Hutchinsonite is sometimes confused with several other red minerals: - **Realgar**: Has a similar color, but usually a more orange hue and resinous luster. Realgar is unstable in light and crystallizes in the monoclinic system. - **Cinnabar**: Is much denser (density approx. 8.1 g/cm³) and has an intensely red streak. It occurs in different geological environments. - **Proustite**: Also has a red color and is light-sensitive, but contains silver and crystallizes in the trigonal system. ## Crystal Forms Hutchinsonite forms flattened, prismatic, or acicular crystals, often with distinct longitudinal striations on their faces. Crystals can form radial aggregates, fan-shaped clusters, or grow as druses in rock fissures.
Geological environment
## Genesis Hutchinsonite is a low-temperature hydrothermal mineral. It forms in ore veins, most often in dolomitic rocks, where it crystallizes from solutions rich in thallium, lead, arsenic, and sulfur. ## Mineral Associations This mineral often co-occurs with other rare sulfosalts. Its most common associated minerals include realgar, orpiment, lorandite, getchellite, smithite, as well as pyrite, sphalerite, and barite. Its associations with other thallium minerals from the Swiss Binn Valley locality are particularly well-known. ## Localities The most important and well-known hutchinsonite localities in the world are: - **Switzerland**: Lengenbach quarry in the Binn Valley (Binntal), Valais canton – the type locality, known for its perfectly formed microcrystals. - **Peru**: Quiruvilca mine in the La Libertad region, from which larger and well-formed specimens originate. - **China**: Jiepaiyu mine in Hunan province, which in recent years has become a source of attractive collector specimens. - **USA**: Small occurrences have been reported in the Carlin area of Nevada.
Rarity
Rare
For collectors
## Quality Criteria The most highly prized hutchinsonite specimens are characterized by sharp, well-terminated crystals of a deep carmine color and high transparency. The intensity of the luster is of great importance – the closer to adamantine, the more attractive the specimen. A contrasting matrix, such as white dolomite, and the presence of other rare associated minerals enhance its value. Due to the generally small size of the crystals, any specimen larger than a few millimeters is considered significant. ## Popular Localities Classic specimens, though usually microscopic, come from the type locality in Lengenbach, Switzerland, and are valued by collectors specializing in rare minerals. Specimens from the Quiruvilca mine in Peru and Hunan province in China are larger and are currently the most commonly found on the collector's market.
Care and storage
## Cleaning Extreme caution must be exercised. Hutchinsonite is very soft and brittle. The safest method is dry cleaning with a soft brush or compressed air from a safe distance. Avoid washing with water, which can react with associated minerals (e.g., realgar). If absolutely necessary, distilled water can be used, and the specimen should be thoroughly dried immediately. ## What to Avoid The mineral is highly toxic due to its thallium and arsenic content. Inhaling dust and contact with mucous membranes must be strictly avoided. Hands should be thoroughly washed after any contact with the specimen. It must not be heated or exposed to acids. It is recommended to protect it from prolonged exposure to intense light, which can cause its slow degradation. ## Storage Hutchinsonite specimens should be stored in closed, airtight containers (e.g., "membrane boxes" or display cases) to prevent accidental contact and the spread of toxic dust. Each container must be clearly labeled with the mineral name and a toxicity warning. Keep away from children and pets.