Theoparacelsite
Chemical formula: Cu²⁺₃(OH)₂As⁵⁺₂O₇(OH)₂
Theoparacelsite is a rare copper arsenate, forming characteristic green, rosette-like aggregates of tiny, platy crystals.
Properties
- Mohs hardness
- 3
- Color
- Dark pistachio green
- Luster
- Vitreous - Adamantine
- Streak
- Yellowish-green
- Density
- 0
- Cleavage
- on {001}
- Fracture
- Conchoidal
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification A characteristic feature of theoparacelsite is its small, platy crystals gathered in fan-shaped or rosette-like aggregates of an intense green color. It occurs in paragenesis with other secondary copper and arsenic minerals. ## Distinguishing from Similar Minerals Theoparacelsite is sometimes confused with other green copper arsenates, such as olivenite, euchroite, or conichalcite. It differs from olivenite by its lighter shade of green and different crystal habit (olivenite most often forms acicular or prismatic crystals). Conichalcite usually occurs in botryoidal or reniform aggregates with a yellowish-green color. Precise identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms The mineral forms very small, flattened, platy crystals, elongated along one axis. These crystals almost always occur in radial, fan-shaped, or spherical aggregates.
Geological environment
## Genesis Theoparacelsite is a secondary mineral, formed in the oxidation zones (so-called iron caps) of copper and arsenic ore deposits. It forms as a result of the weathering of primary sulfides, such as chalcopyrite and arsenopyrite, in the presence of water and oxygen. ## Mineral Associations This mineral co-occurs with other secondary minerals of the oxidation zone. It is most commonly found in association with quartz, olivenite, conichalcite, azurite, malachite, tyrolite, as well as iron oxides (goethite, hematite). ## Localities The most important and classic localities for theoparacelsite worldwide are the Tsumeb Mine in Namibia (type locality) and the Sterling Hill Mine in Ogdensburg, New Jersey, USA. It is also known from small occurrences in Greece (Lavrion) and Germany (Black Forest).
Rarity
Rare
For collectors
## Quality Criteria The most highly valued by collectors are specimens with well-formed, rosette-like or fan-shaped aggregates of intense, emerald-green color. Contrast with the rock matrix (e.g., with white quartz) and the absence of damage to the delicate crystals are important. Due to the small size of the crystals, theoparacelsite is primarily of interest to collectors specializing in microminerals (so-called micromounting). ## Popular Localities Specimens from the Tsumeb Mine in Namibia are considered the best in the world and serve as the standard for this mineral. Specimens from Sterling Hill in the USA are also highly valued.
Care and storage
## Cleaning Theoparacelsite specimens are very delicate and brittle. They should only be cleaned with compressed air to remove dust. The use of water, and especially ultrasonics, is highly inadvisable and can lead to the destruction of the fine crystals. ## What to Avoid Avoid contact with all chemicals, acids, and detergents. The mineral is sensitive to high temperatures and mechanical shocks. As an arsenate, it is toxic – avoid inhaling dust and wash hands after any contact with the specimen. ## Storage Collector's specimens of theoparacelsite should be stored in closed, stable containers (so-called "micromount boxes") to protect them from dust, moisture, and mechanical damage. They should not be exposed to direct sunlight.