Tooeleite
Chemical formula: Fe³⁺₆(As³⁺O₃)₄S⁶⁺O₄(OH)₄·4H₂O
Tooeleite is a rare, secondary iron arsenate-sulfate, forming microscopic, yellowish-brown crystals in the oxidation zones of polymetallic deposits.
Properties
- Mohs hardness
- 3
- Color
- Orange
- Luster
- Silky
- Streak
- orange
- Density
- 4.23
- Cleavage
- One good normal to [001]
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of tooeleite is based on its characteristic appearance – fine, acicular, yellowish-brown crystals forming crusts and aggregates. Its environment of occurrence is also crucial: oxidation zones of arsenic deposits, often associated with scorodite and pharmacosiderite. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Tooeleite can be confused with other secondary arsenic minerals of similar color, such as pharmacosiderite, yukonite, or pitticite. Pharmacosiderite often forms cubic crystals, in contrast to the acicular crystals of tooeleite. Yukonite and pitticite are usually amorphous and have a resinous or vitreous luster, while tooeleite forms distinct, though small, crystals with a silky luster. ## Crystal Forms Tooeleite crystallizes as very small, elongated crystals with an acicular or bladed habit. These crystals often combine into stellate, radial, or disordered aggregates, and also form thin crusts on host rocks.
Geological environment
## Genesis Tooeleite is a secondary mineral, formed in the oxidation (weathering) zones of ore deposits rich in arsenic, especially arsenopyrite. It forms under low pH (acidic) conditions as a result of the oxidation of primary arsenic minerals and iron sulfides. ## Mineral Associations This mineral often co-occurs with other oxidation products, such as scorodite, pharmacosiderite, jarosite, gypsum, quartz, and iron oxides (e.g., goethite). ## Localities The most important and well-documented tooeleite localities worldwide include: - U.S. Mine in Gold Hill, Tooele County, Utah, USA (type locality). - Clara Mine in Rankach Valley, Wolfach, Black Forest, Germany. - Oumlampo Mine in Okayama Prefecture, Japan. - Vrančice polymetallic deposit, Příbram, Czech Republic.
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of tooeleite specimens primarily depends on the richness and aesthetics of the microcrystalline aggregates. Most valued are specimens showing well-formed, though microscopic, crystals forming dense crusts or radial groups. A contrasting color of the rock matrix can enhance the visual appeal of the specimen. Due to the nature of the mineral, the purity and size of individual crystals are not key criteria. ## Popular Localities The most known and valued specimens, often serving as a benchmark for this mineral, come from the type locality at the U.S. Mine in Utah, USA. Good quality microcrystals also originate from the Clara Mine in Germany, which is known for its abundance of rare secondary minerals.
Care and storage
## Cleaning Tooeleite specimens are extremely delicate and fragile. Mechanical or chemical cleaning is not recommended. Any contaminants, such as dust, should be removed very carefully using a photographic air blower or a stream of compressed air from a distance. ## What to Avoid Avoid contact with water and any chemicals that could dissolve or damage the microscopic crystals. The mineral is sensitive to shocks and vibrations. It should not be heated or exposed to ultrasound. ## Storage Specimens should be stored in sealed, padded "micromount" boxes to protect them from mechanical damage, dust, and humidity. Storage under stable room conditions is sufficient.